vfs: fix freevnodes count update race against preemption

[FreeBSD/FreeBSD.git] / sys / kern / vfs_subr.c

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)vfs_subr.c  8.31 (Berkeley) 5/26/95
 */

/*
 * External virtual filesystem routines
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_ddb.h"
#include "opt_watchdog.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/bio.h>
#include <sys/buf.h>
#include <sys/capsicum.h>
#include <sys/condvar.h>
#include <sys/conf.h>
#include <sys/counter.h>
#include <sys/dirent.h>
#include <sys/event.h>
#include <sys/eventhandler.h>
#include <sys/extattr.h>
#include <sys/file.h>
#include <sys/fcntl.h>
#include <sys/jail.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/ktr.h>
#include <sys/lockf.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/pctrie.h>
#include <sys/priv.h>
#include <sys/reboot.h>
#include <sys/refcount.h>
#include <sys/rwlock.h>
#include <sys/sched.h>
#include <sys/sleepqueue.h>
#include <sys/smp.h>
#include <sys/stat.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <sys/watchdog.h>

#include <machine/stdarg.h>

#include <security/mac/mac_framework.h>

#include <vm/vm.h>
#include <vm/vm_object.h>
#include <vm/vm_extern.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>
#include <vm/vm_kern.h>
#include <vm/uma.h>

#ifdef DDB
#include <ddb/ddb.h>
#endif

static void     delmntque(struct vnode *vp);
static int      flushbuflist(struct bufv *bufv, int flags, struct bufobj *bo,
                    int slpflag, int slptimeo);
static void     syncer_shutdown(void *arg, int howto);
static int      vtryrecycle(struct vnode *vp);
static void     v_init_counters(struct vnode *);
static void     v_incr_devcount(struct vnode *);
static void     v_decr_devcount(struct vnode *);
static void     vgonel(struct vnode *);
static void     vfs_knllock(void *arg);
static void     vfs_knlunlock(void *arg);
static void     vfs_knl_assert_locked(void *arg);
static void     vfs_knl_assert_unlocked(void *arg);
static void     destroy_vpollinfo(struct vpollinfo *vi);
static int      v_inval_buf_range_locked(struct vnode *vp, struct bufobj *bo,
                    daddr_t startlbn, daddr_t endlbn);
static void     vnlru_recalc(void);

/*
 * These fences are intended for cases where some synchronization is
 * needed between access of v_iflags and lockless vnode refcount (v_holdcnt
 * and v_usecount) updates.  Access to v_iflags is generally synchronized
 * by the interlock, but we have some internal assertions that check vnode
 * flags without acquiring the lock.  Thus, these fences are INVARIANTS-only
 * for now.
 */
#ifdef INVARIANTS
#define VNODE_REFCOUNT_FENCE_ACQ()      atomic_thread_fence_acq()
#define VNODE_REFCOUNT_FENCE_REL()      atomic_thread_fence_rel()
#else
#define VNODE_REFCOUNT_FENCE_ACQ()
#define VNODE_REFCOUNT_FENCE_REL()
#endif

/*
 * Number of vnodes in existence.  Increased whenever getnewvnode()
 * allocates a new vnode, decreased in vdropl() for VIRF_DOOMED vnode.
 */
static u_long __exclusive_cache_line numvnodes;

SYSCTL_ULONG(_vfs, OID_AUTO, numvnodes, CTLFLAG_RD, &numvnodes, 0,
    "Number of vnodes in existence");

static counter_u64_t vnodes_created;
SYSCTL_COUNTER_U64(_vfs, OID_AUTO, vnodes_created, CTLFLAG_RD, &vnodes_created,
    "Number of vnodes created by getnewvnode");

/*
 * Conversion tables for conversion from vnode types to inode formats
 * and back.
 */
enum vtype iftovt_tab[16] = {
        VNON, VFIFO, VCHR, VNON, VDIR, VNON, VBLK, VNON,
        VREG, VNON, VLNK, VNON, VSOCK, VNON, VNON, VNON
};
int vttoif_tab[10] = {
        0, S_IFREG, S_IFDIR, S_IFBLK, S_IFCHR, S_IFLNK,
        S_IFSOCK, S_IFIFO, S_IFMT, S_IFMT
};

/*
 * List of allocates vnodes in the system.
 */
static TAILQ_HEAD(freelst, vnode) vnode_list;
static struct vnode *vnode_list_free_marker;
static struct vnode *vnode_list_reclaim_marker;

/*
 * "Free" vnode target.  Free vnodes are rarely completely free, but are
 * just ones that are cheap to recycle.  Usually they are for files which
 * have been stat'd but not read; these usually have inode and namecache
 * data attached to them.  This target is the preferred minimum size of a
 * sub-cache consisting mostly of such files. The system balances the size
 * of this sub-cache with its complement to try to prevent either from
 * thrashing while the other is relatively inactive.  The targets express
 * a preference for the best balance.
 *
 * "Above" this target there are 2 further targets (watermarks) related
 * to recyling of free vnodes.  In the best-operating case, the cache is
 * exactly full, the free list has size between vlowat and vhiwat above the
 * free target, and recycling from it and normal use maintains this state.
 * Sometimes the free list is below vlowat or even empty, but this state
 * is even better for immediate use provided the cache is not full.
 * Otherwise, vnlru_proc() runs to reclaim enough vnodes (usually non-free
 * ones) to reach one of these states.  The watermarks are currently hard-
 * coded as 4% and 9% of the available space higher.  These and the default
 * of 25% for wantfreevnodes are too large if the memory size is large.
 * E.g., 9% of 75% of MAXVNODES is more than 566000 vnodes to reclaim
 * whenever vnlru_proc() becomes active.
 */
static long wantfreevnodes;
static long __exclusive_cache_line freevnodes;
SYSCTL_ULONG(_vfs, OID_AUTO, freevnodes, CTLFLAG_RD,
    &freevnodes, 0, "Number of \"free\" vnodes");
static long freevnodes_old;

static counter_u64_t recycles_count;
SYSCTL_COUNTER_U64(_vfs, OID_AUTO, recycles, CTLFLAG_RD, &recycles_count,
    "Number of vnodes recycled to meet vnode cache targets");

static counter_u64_t recycles_free_count;
SYSCTL_COUNTER_U64(_vfs, OID_AUTO, recycles_free, CTLFLAG_RD, &recycles_free_count,
    "Number of free vnodes recycled to meet vnode cache targets");

/*
 * Various variables used for debugging the new implementation of
 * reassignbuf().
 * XXX these are probably of (very) limited utility now.
 */
static int reassignbufcalls;
SYSCTL_INT(_vfs, OID_AUTO, reassignbufcalls, CTLFLAG_RW | CTLFLAG_STATS,
    &reassignbufcalls, 0, "Number of calls to reassignbuf");

static counter_u64_t deferred_inact;
SYSCTL_COUNTER_U64(_vfs, OID_AUTO, deferred_inact, CTLFLAG_RD, &deferred_inact,
    "Number of times inactive processing was deferred");

/* To keep more than one thread at a time from running vfs_getnewfsid */
static struct mtx mntid_mtx;

/*
 * Lock for any access to the following:
 *      vnode_list
 *      numvnodes
 *      freevnodes
 */
static struct mtx __exclusive_cache_line vnode_list_mtx;

/* Publicly exported FS */
struct nfs_public nfs_pub;

static uma_zone_t buf_trie_zone;

/* Zone for allocation of new vnodes - used exclusively by getnewvnode() */
static uma_zone_t vnode_zone;
static uma_zone_t vnodepoll_zone;

/*
 * The workitem queue.
 *
 * It is useful to delay writes of file data and filesystem metadata
 * for tens of seconds so that quickly created and deleted files need
 * not waste disk bandwidth being created and removed. To realize this,
 * we append vnodes to a "workitem" queue. When running with a soft
 * updates implementation, most pending metadata dependencies should
 * not wait for more than a few seconds. Thus, mounted on block devices
 * are delayed only about a half the time that file data is delayed.
 * Similarly, directory updates are more critical, so are only delayed
 * about a third the time that file data is delayed. Thus, there are
 * SYNCER_MAXDELAY queues that are processed round-robin at a rate of
 * one each second (driven off the filesystem syncer process). The
 * syncer_delayno variable indicates the next queue that is to be processed.
 * Items that need to be processed soon are placed in this queue:
 *
 *      syncer_workitem_pending[syncer_delayno]
 *
 * A delay of fifteen seconds is done by placing the request fifteen
 * entries later in the queue:
 *
 *      syncer_workitem_pending[(syncer_delayno + 15) & syncer_mask]
 *
 */
static int syncer_delayno;
static long syncer_mask;
LIST_HEAD(synclist, bufobj);
static struct synclist *syncer_workitem_pending;
/*
 * The sync_mtx protects:
 *      bo->bo_synclist
 *      sync_vnode_count
 *      syncer_delayno
 *      syncer_state
 *      syncer_workitem_pending
 *      syncer_worklist_len
 *      rushjob
 */
static struct mtx sync_mtx;
static struct cv sync_wakeup;

#define SYNCER_MAXDELAY         32
static int syncer_maxdelay = SYNCER_MAXDELAY;   /* maximum delay time */
static int syncdelay = 30;              /* max time to delay syncing data */
static int filedelay = 30;              /* time to delay syncing files */
SYSCTL_INT(_kern, OID_AUTO, filedelay, CTLFLAG_RW, &filedelay, 0,
    "Time to delay syncing files (in seconds)");
static int dirdelay = 29;               /* time to delay syncing directories */
SYSCTL_INT(_kern, OID_AUTO, dirdelay, CTLFLAG_RW, &dirdelay, 0,
    "Time to delay syncing directories (in seconds)");
static int metadelay = 28;              /* time to delay syncing metadata */
SYSCTL_INT(_kern, OID_AUTO, metadelay, CTLFLAG_RW, &metadelay, 0,
    "Time to delay syncing metadata (in seconds)");
static int rushjob;             /* number of slots to run ASAP */
static int stat_rush_requests;  /* number of times I/O speeded up */
SYSCTL_INT(_debug, OID_AUTO, rush_requests, CTLFLAG_RW, &stat_rush_requests, 0,
    "Number of times I/O speeded up (rush requests)");

#define VDBATCH_SIZE 8
struct vdbatch {
        u_int index;
        long freevnodes;
        struct mtx lock;
        struct vnode *tab[VDBATCH_SIZE];
};
DPCPU_DEFINE_STATIC(struct vdbatch, vd);

static void     vdbatch_dequeue(struct vnode *vp);

/*
 * When shutting down the syncer, run it at four times normal speed.
 */
#define SYNCER_SHUTDOWN_SPEEDUP         4
static int sync_vnode_count;
static int syncer_worklist_len;
static enum { SYNCER_RUNNING, SYNCER_SHUTTING_DOWN, SYNCER_FINAL_DELAY }
    syncer_state;

/* Target for maximum number of vnodes. */
u_long desiredvnodes;
static u_long gapvnodes;                /* gap between wanted and desired */
static u_long vhiwat;           /* enough extras after expansion */
static u_long vlowat;           /* minimal extras before expansion */
static u_long vstir;            /* nonzero to stir non-free vnodes */
static volatile int vsmalltrigger = 8;  /* pref to keep if > this many pages */

static u_long vnlru_read_freevnodes(void);

/*
 * Note that no attempt is made to sanitize these parameters.
 */
static int
sysctl_maxvnodes(SYSCTL_HANDLER_ARGS)
{
        u_long val;
        int error;

        val = desiredvnodes;
        error = sysctl_handle_long(oidp, &val, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);

        if (val == desiredvnodes)
                return (0);
        mtx_lock(&vnode_list_mtx);
        desiredvnodes = val;
        wantfreevnodes = desiredvnodes / 4;
        vnlru_recalc();
        mtx_unlock(&vnode_list_mtx);
        /*
         * XXX There is no protection against multiple threads changing
         * desiredvnodes at the same time. Locking above only helps vnlru and
         * getnewvnode.
         */
        vfs_hash_changesize(desiredvnodes);
        cache_changesize(desiredvnodes);
        return (0);
}

SYSCTL_PROC(_kern, KERN_MAXVNODES, maxvnodes,
    CTLTYPE_ULONG | CTLFLAG_MPSAFE | CTLFLAG_RW, NULL, 0, sysctl_maxvnodes,
    "UL", "Target for maximum number of vnodes");

static int
sysctl_wantfreevnodes(SYSCTL_HANDLER_ARGS)
{
        u_long val;
        int error;

        val = wantfreevnodes;
        error = sysctl_handle_long(oidp, &val, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);

        if (val == wantfreevnodes)
                return (0);
        mtx_lock(&vnode_list_mtx);
        wantfreevnodes = val;
        vnlru_recalc();
        mtx_unlock(&vnode_list_mtx);
        return (0);
}

SYSCTL_PROC(_vfs, OID_AUTO, wantfreevnodes,
    CTLTYPE_ULONG | CTLFLAG_MPSAFE | CTLFLAG_RW, NULL, 0, sysctl_wantfreevnodes,
    "UL", "Target for minimum number of \"free\" vnodes");

SYSCTL_ULONG(_kern, OID_AUTO, minvnodes, CTLFLAG_RW,
    &wantfreevnodes, 0, "Old name for vfs.wantfreevnodes (legacy)");
static int vnlru_nowhere;
SYSCTL_INT(_debug, OID_AUTO, vnlru_nowhere, CTLFLAG_RW,
    &vnlru_nowhere, 0, "Number of times the vnlru process ran without success");

static int
sysctl_try_reclaim_vnode(SYSCTL_HANDLER_ARGS)
{
        struct vnode *vp;
        struct nameidata nd;
        char *buf;
        unsigned long ndflags;
        int error;

        if (req->newptr == NULL)
                return (EINVAL);
        if (req->newlen >= PATH_MAX)
                return (E2BIG);

        buf = malloc(PATH_MAX, M_TEMP, M_WAITOK);
        error = SYSCTL_IN(req, buf, req->newlen);
        if (error != 0)
                goto out;

        buf[req->newlen] = '\0';

        ndflags = LOCKLEAF | NOFOLLOW | AUDITVNODE1 | NOCACHE | SAVENAME;
        NDINIT(&nd, LOOKUP, ndflags, UIO_SYSSPACE, buf, curthread);
        if ((error = namei(&nd)) != 0)
                goto out;
        vp = nd.ni_vp;

        if (VN_IS_DOOMED(vp)) {
                /*
                 * This vnode is being recycled.  Return != 0 to let the caller
                 * know that the sysctl had no effect.  Return EAGAIN because a
                 * subsequent call will likely succeed (since namei will create
                 * a new vnode if necessary)
                 */
                error = EAGAIN;
                goto putvnode;
        }

        counter_u64_add(recycles_count, 1);
        vgone(vp);
putvnode:
        NDFREE(&nd, 0);
out:
        free(buf, M_TEMP);
        return (error);
}

static int
sysctl_ftry_reclaim_vnode(SYSCTL_HANDLER_ARGS)
{
        struct thread *td = curthread;
        struct vnode *vp;
        struct file *fp;
        int error;
        int fd;

        if (req->newptr == NULL)
                return (EBADF);

        error = sysctl_handle_int(oidp, &fd, 0, req);
        if (error != 0)
                return (error);
        error = getvnode(curthread, fd, &cap_fcntl_rights, &fp);
        if (error != 0)
                return (error);
        vp = fp->f_vnode;

        error = vn_lock(vp, LK_EXCLUSIVE);
        if (error != 0)
                goto drop;

        counter_u64_add(recycles_count, 1);
        vgone(vp);
        VOP_UNLOCK(vp);
drop:
        fdrop(fp, td);
        return (error);
}

SYSCTL_PROC(_debug, OID_AUTO, try_reclaim_vnode,
    CTLTYPE_STRING | CTLFLAG_MPSAFE | CTLFLAG_WR, NULL, 0,
    sysctl_try_reclaim_vnode, "A", "Try to reclaim a vnode by its pathname");
SYSCTL_PROC(_debug, OID_AUTO, ftry_reclaim_vnode,
    CTLTYPE_INT | CTLFLAG_MPSAFE | CTLFLAG_WR, NULL, 0,
    sysctl_ftry_reclaim_vnode, "I",
    "Try to reclaim a vnode by its file descriptor");

/* Shift count for (uintptr_t)vp to initialize vp->v_hash. */
static int vnsz2log;

/*
 * Support for the bufobj clean & dirty pctrie.
 */
static void *
buf_trie_alloc(struct pctrie *ptree)
{

        return uma_zalloc(buf_trie_zone, M_NOWAIT);
}

static void
buf_trie_free(struct pctrie *ptree, void *node)
{

        uma_zfree(buf_trie_zone, node);
}
PCTRIE_DEFINE(BUF, buf, b_lblkno, buf_trie_alloc, buf_trie_free);

/*
 * Initialize the vnode management data structures.
 *
 * Reevaluate the following cap on the number of vnodes after the physical
 * memory size exceeds 512GB.  In the limit, as the physical memory size
 * grows, the ratio of the memory size in KB to vnodes approaches 64:1.
 */
#ifndef MAXVNODES_MAX
#define MAXVNODES_MAX   (512UL * 1024 * 1024 / 64)      /* 8M */
#endif

static MALLOC_DEFINE(M_VNODE_MARKER, "vnodemarker", "vnode marker");

static struct vnode *
vn_alloc_marker(struct mount *mp)
{
        struct vnode *vp;

        vp = malloc(sizeof(struct vnode), M_VNODE_MARKER, M_WAITOK | M_ZERO);
        vp->v_type = VMARKER;
        vp->v_mount = mp;

        return (vp);
}

static void
vn_free_marker(struct vnode *vp)
{

        MPASS(vp->v_type == VMARKER);
        free(vp, M_VNODE_MARKER);
}

/*
 * Initialize a vnode as it first enters the zone.
 */
static int
vnode_init(void *mem, int size, int flags)
{
        struct vnode *vp;

        vp = mem;
        bzero(vp, size);
        /*
         * Setup locks.
         */
        vp->v_vnlock = &vp->v_lock;
        mtx_init(&vp->v_interlock, "vnode interlock", NULL, MTX_DEF);
        /*
         * By default, don't allow shared locks unless filesystems opt-in.
         */
        lockinit(vp->v_vnlock, PVFS, "vnode", VLKTIMEOUT,
            LK_NOSHARE | LK_IS_VNODE);
        /*
         * Initialize bufobj.
         */
        bufobj_init(&vp->v_bufobj, vp);
        /*
         * Initialize namecache.
         */
        LIST_INIT(&vp->v_cache_src);
        TAILQ_INIT(&vp->v_cache_dst);
        /*
         * Initialize rangelocks.
         */
        rangelock_init(&vp->v_rl);

        vp->v_dbatchcpu = NOCPU;

        mtx_lock(&vnode_list_mtx);
        TAILQ_INSERT_BEFORE(vnode_list_free_marker, vp, v_vnodelist);
        mtx_unlock(&vnode_list_mtx);
        return (0);
}

/*
 * Free a vnode when it is cleared from the zone.
 */
static void
vnode_fini(void *mem, int size)
{
        struct vnode *vp;
        struct bufobj *bo;

        vp = mem;
        vdbatch_dequeue(vp);
        mtx_lock(&vnode_list_mtx);
        TAILQ_REMOVE(&vnode_list, vp, v_vnodelist);
        mtx_unlock(&vnode_list_mtx);
        rangelock_destroy(&vp->v_rl);
        lockdestroy(vp->v_vnlock);
        mtx_destroy(&vp->v_interlock);
        bo = &vp->v_bufobj;
        rw_destroy(BO_LOCKPTR(bo));
}

/*
 * Provide the size of NFS nclnode and NFS fh for calculation of the
 * vnode memory consumption.  The size is specified directly to
 * eliminate dependency on NFS-private header.
 *
 * Other filesystems may use bigger or smaller (like UFS and ZFS)
 * private inode data, but the NFS-based estimation is ample enough.
 * Still, we care about differences in the size between 64- and 32-bit
 * platforms.
 *
 * Namecache structure size is heuristically
 * sizeof(struct namecache_ts) + CACHE_PATH_CUTOFF + 1.
 */
#ifdef _LP64
#define NFS_NCLNODE_SZ  (528 + 64)
#define NC_SZ           148
#else
#define NFS_NCLNODE_SZ  (360 + 32)
#define NC_SZ           92
#endif

static void
vntblinit(void *dummy __unused)
{
        struct vdbatch *vd;
        int cpu, physvnodes, virtvnodes;
        u_int i;

        /*
         * Desiredvnodes is a function of the physical memory size and the
         * kernel's heap size.  Generally speaking, it scales with the
         * physical memory size.  The ratio of desiredvnodes to the physical
         * memory size is 1:16 until desiredvnodes exceeds 98,304.
         * Thereafter, the
         * marginal ratio of desiredvnodes to the physical memory size is
         * 1:64.  However, desiredvnodes is limited by the kernel's heap
         * size.  The memory required by desiredvnodes vnodes and vm objects
         * must not exceed 1/10th of the kernel's heap size.
         */
        physvnodes = maxproc + pgtok(vm_cnt.v_page_count) / 64 +
            3 * min(98304 * 16, pgtok(vm_cnt.v_page_count)) / 64;
        virtvnodes = vm_kmem_size / (10 * (sizeof(struct vm_object) +
            sizeof(struct vnode) + NC_SZ * ncsizefactor + NFS_NCLNODE_SZ));
        desiredvnodes = min(physvnodes, virtvnodes);
        if (desiredvnodes > MAXVNODES_MAX) {
                if (bootverbose)
                        printf("Reducing kern.maxvnodes %lu -> %lu\n",
                            desiredvnodes, MAXVNODES_MAX);
                desiredvnodes = MAXVNODES_MAX;
        }
        wantfreevnodes = desiredvnodes / 4;
        mtx_init(&mntid_mtx, "mntid", NULL, MTX_DEF);
        TAILQ_INIT(&vnode_list);
        mtx_init(&vnode_list_mtx, "vnode_list", NULL, MTX_DEF);
        /*
         * The lock is taken to appease WITNESS.
         */
        mtx_lock(&vnode_list_mtx);
        vnlru_recalc();
        mtx_unlock(&vnode_list_mtx);
        vnode_list_free_marker = vn_alloc_marker(NULL);
        TAILQ_INSERT_HEAD(&vnode_list, vnode_list_free_marker, v_vnodelist);
        vnode_list_reclaim_marker = vn_alloc_marker(NULL);
        TAILQ_INSERT_HEAD(&vnode_list, vnode_list_reclaim_marker, v_vnodelist);
        vnode_zone = uma_zcreate("VNODE", sizeof (struct vnode), NULL, NULL,
            vnode_init, vnode_fini, UMA_ALIGN_PTR, 0);
        vnodepoll_zone = uma_zcreate("VNODEPOLL", sizeof (struct vpollinfo),
            NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
        /*
         * Preallocate enough nodes to support one-per buf so that
         * we can not fail an insert.  reassignbuf() callers can not
         * tolerate the insertion failure.
         */
        buf_trie_zone = uma_zcreate("BUF TRIE", pctrie_node_size(),
            NULL, NULL, pctrie_zone_init, NULL, UMA_ALIGN_PTR, 
            UMA_ZONE_NOFREE | UMA_ZONE_VM);
        uma_prealloc(buf_trie_zone, nbuf);

        vnodes_created = counter_u64_alloc(M_WAITOK);
        recycles_count = counter_u64_alloc(M_WAITOK);
        recycles_free_count = counter_u64_alloc(M_WAITOK);
        deferred_inact = counter_u64_alloc(M_WAITOK);

        /*
         * Initialize the filesystem syncer.
         */
        syncer_workitem_pending = hashinit(syncer_maxdelay, M_VNODE,
            &syncer_mask);
        syncer_maxdelay = syncer_mask + 1;
        mtx_init(&sync_mtx, "Syncer mtx", NULL, MTX_DEF);
        cv_init(&sync_wakeup, "syncer");
        for (i = 1; i <= sizeof(struct vnode); i <<= 1)
                vnsz2log++;
        vnsz2log--;

        CPU_FOREACH(cpu) {
                vd = DPCPU_ID_PTR((cpu), vd);
                bzero(vd, sizeof(*vd));
                mtx_init(&vd->lock, "vdbatch", NULL, MTX_DEF);
        }
}
SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_FIRST, vntblinit, NULL);


/*
 * Mark a mount point as busy. Used to synchronize access and to delay
 * unmounting. Eventually, mountlist_mtx is not released on failure.
 *
 * vfs_busy() is a custom lock, it can block the caller.
 * vfs_busy() only sleeps if the unmount is active on the mount point.
 * For a mountpoint mp, vfs_busy-enforced lock is before lock of any
 * vnode belonging to mp.
 *
 * Lookup uses vfs_busy() to traverse mount points.
 * root fs                      var fs
 * / vnode lock         A       / vnode lock (/var)             D
 * /var vnode lock      B       /log vnode lock(/var/log)       E
 * vfs_busy lock        C       vfs_busy lock                   F
 *
 * Within each file system, the lock order is C->A->B and F->D->E.
 *
 * When traversing across mounts, the system follows that lock order:
 *
 *        C->A->B
 *              |
 *              +->F->D->E
 *
 * The lookup() process for namei("/var") illustrates the process:
 *  VOP_LOOKUP() obtains B while A is held
 *  vfs_busy() obtains a shared lock on F while A and B are held
 *  vput() releases lock on B
 *  vput() releases lock on A
 *  VFS_ROOT() obtains lock on D while shared lock on F is held
 *  vfs_unbusy() releases shared lock on F
 *  vn_lock() obtains lock on deadfs vnode vp_crossmp instead of A.
 *    Attempt to lock A (instead of vp_crossmp) while D is held would
 *    violate the global order, causing deadlocks.
 *
 * dounmount() locks B while F is drained.
 */
int
vfs_busy(struct mount *mp, int flags)
{

        MPASS((flags & ~MBF_MASK) == 0);
        CTR3(KTR_VFS, "%s: mp %p with flags %d", __func__, mp, flags);

        if (vfs_op_thread_enter(mp)) {
                MPASS((mp->mnt_kern_flag & MNTK_DRAINING) == 0);
                MPASS((mp->mnt_kern_flag & MNTK_UNMOUNT) == 0);
                MPASS((mp->mnt_kern_flag & MNTK_REFEXPIRE) == 0);
                vfs_mp_count_add_pcpu(mp, ref, 1);
                vfs_mp_count_add_pcpu(mp, lockref, 1);
                vfs_op_thread_exit(mp);
                if (flags & MBF_MNTLSTLOCK)
                        mtx_unlock(&mountlist_mtx);
                return (0);
        }

        MNT_ILOCK(mp);
        vfs_assert_mount_counters(mp);
        MNT_REF(mp);
        /*
         * If mount point is currently being unmounted, sleep until the
         * mount point fate is decided.  If thread doing the unmounting fails,
         * it will clear MNTK_UNMOUNT flag before waking us up, indicating
         * that this mount point has survived the unmount attempt and vfs_busy
         * should retry.  Otherwise the unmounter thread will set MNTK_REFEXPIRE
         * flag in addition to MNTK_UNMOUNT, indicating that mount point is
         * about to be really destroyed.  vfs_busy needs to release its
         * reference on the mount point in this case and return with ENOENT,
         * telling the caller that mount mount it tried to busy is no longer
         * valid.
         */
        while (mp->mnt_kern_flag & MNTK_UNMOUNT) {
                if (flags & MBF_NOWAIT || mp->mnt_kern_flag & MNTK_REFEXPIRE) {
                        MNT_REL(mp);
                        MNT_IUNLOCK(mp);
                        CTR1(KTR_VFS, "%s: failed busying before sleeping",
                            __func__);
                        return (ENOENT);
                }
                if (flags & MBF_MNTLSTLOCK)
                        mtx_unlock(&mountlist_mtx);
                mp->mnt_kern_flag |= MNTK_MWAIT;
                msleep(mp, MNT_MTX(mp), PVFS | PDROP, "vfs_busy", 0);
                if (flags & MBF_MNTLSTLOCK)
                        mtx_lock(&mountlist_mtx);
                MNT_ILOCK(mp);
        }
        if (flags & MBF_MNTLSTLOCK)
                mtx_unlock(&mountlist_mtx);
        mp->mnt_lockref++;
        MNT_IUNLOCK(mp);
        return (0);
}

/*
 * Free a busy filesystem.
 */
void
vfs_unbusy(struct mount *mp)
{
        int c;

        CTR2(KTR_VFS, "%s: mp %p", __func__, mp);

        if (vfs_op_thread_enter(mp)) {
                MPASS((mp->mnt_kern_flag & MNTK_DRAINING) == 0);
                vfs_mp_count_sub_pcpu(mp, lockref, 1);
                vfs_mp_count_sub_pcpu(mp, ref, 1);
                vfs_op_thread_exit(mp);
                return;
        }

        MNT_ILOCK(mp);
        vfs_assert_mount_counters(mp);
        MNT_REL(mp);
        c = --mp->mnt_lockref;
        if (mp->mnt_vfs_ops == 0) {
                MPASS((mp->mnt_kern_flag & MNTK_DRAINING) == 0);
                MNT_IUNLOCK(mp);
                return;
        }
        if (c < 0)
                vfs_dump_mount_counters(mp);
        if (c == 0 && (mp->mnt_kern_flag & MNTK_DRAINING) != 0) {
                MPASS(mp->mnt_kern_flag & MNTK_UNMOUNT);
                CTR1(KTR_VFS, "%s: waking up waiters", __func__);
                mp->mnt_kern_flag &= ~MNTK_DRAINING;
                wakeup(&mp->mnt_lockref);
        }
        MNT_IUNLOCK(mp);
}

/*
 * Lookup a mount point by filesystem identifier.
 */
struct mount *
vfs_getvfs(fsid_t *fsid)
{
        struct mount *mp;

        CTR2(KTR_VFS, "%s: fsid %p", __func__, fsid);
        mtx_lock(&mountlist_mtx);
        TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                if (mp->mnt_stat.f_fsid.val[0] == fsid->val[0] &&
                    mp->mnt_stat.f_fsid.val[1] == fsid->val[1]) {
                        vfs_ref(mp);
                        mtx_unlock(&mountlist_mtx);
                        return (mp);
                }
        }
        mtx_unlock(&mountlist_mtx);
        CTR2(KTR_VFS, "%s: lookup failed for %p id", __func__, fsid);
        return ((struct mount *) 0);
}

/*
 * Lookup a mount point by filesystem identifier, busying it before
 * returning.
 *
 * To avoid congestion on mountlist_mtx, implement simple direct-mapped
 * cache for popular filesystem identifiers.  The cache is lockess, using
 * the fact that struct mount's are never freed.  In worst case we may
 * get pointer to unmounted or even different filesystem, so we have to
 * check what we got, and go slow way if so.
 */
struct mount *
vfs_busyfs(fsid_t *fsid)
{
#define FSID_CACHE_SIZE 256
        typedef struct mount * volatile vmp_t;
        static vmp_t cache[FSID_CACHE_SIZE];
        struct mount *mp;
        int error;
        uint32_t hash;

        CTR2(KTR_VFS, "%s: fsid %p", __func__, fsid);
        hash = fsid->val[0] ^ fsid->val[1];
        hash = (hash >> 16 ^ hash) & (FSID_CACHE_SIZE - 1);
        mp = cache[hash];
        if (mp == NULL ||
            mp->mnt_stat.f_fsid.val[0] != fsid->val[0] ||
            mp->mnt_stat.f_fsid.val[1] != fsid->val[1])
                goto slow;
        if (vfs_busy(mp, 0) != 0) {
                cache[hash] = NULL;
                goto slow;
        }
        if (mp->mnt_stat.f_fsid.val[0] == fsid->val[0] &&
            mp->mnt_stat.f_fsid.val[1] == fsid->val[1])
                return (mp);
        else
            vfs_unbusy(mp);

slow:
        mtx_lock(&mountlist_mtx);
        TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                if (mp->mnt_stat.f_fsid.val[0] == fsid->val[0] &&
                    mp->mnt_stat.f_fsid.val[1] == fsid->val[1]) {
                        error = vfs_busy(mp, MBF_MNTLSTLOCK);
                        if (error) {
                                cache[hash] = NULL;
                                mtx_unlock(&mountlist_mtx);
                                return (NULL);
                        }
                        cache[hash] = mp;
                        return (mp);
                }
        }
        CTR2(KTR_VFS, "%s: lookup failed for %p id", __func__, fsid);
        mtx_unlock(&mountlist_mtx);
        return ((struct mount *) 0);
}

/*
 * Check if a user can access privileged mount options.
 */
int
vfs_suser(struct mount *mp, struct thread *td)
{
        int error;

        if (jailed(td->td_ucred)) {
                /*
                 * If the jail of the calling thread lacks permission for
                 * this type of file system, deny immediately.
                 */
                if (!prison_allow(td->td_ucred, mp->mnt_vfc->vfc_prison_flag))
                        return (EPERM);

                /*
                 * If the file system was mounted outside the jail of the
                 * calling thread, deny immediately.
                 */
                if (prison_check(td->td_ucred, mp->mnt_cred) != 0)
                        return (EPERM);
        }

        /*
         * If file system supports delegated administration, we don't check
         * for the PRIV_VFS_MOUNT_OWNER privilege - it will be better verified
         * by the file system itself.
         * If this is not the user that did original mount, we check for
         * the PRIV_VFS_MOUNT_OWNER privilege.
         */
        if (!(mp->mnt_vfc->vfc_flags & VFCF_DELEGADMIN) &&
            mp->mnt_cred->cr_uid != td->td_ucred->cr_uid) {
                if ((error = priv_check(td, PRIV_VFS_MOUNT_OWNER)) != 0)
                        return (error);
        }
        return (0);
}

/*
 * Get a new unique fsid.  Try to make its val[0] unique, since this value
 * will be used to create fake device numbers for stat().  Also try (but
 * not so hard) make its val[0] unique mod 2^16, since some emulators only
 * support 16-bit device numbers.  We end up with unique val[0]'s for the
 * first 2^16 calls and unique val[0]'s mod 2^16 for the first 2^8 calls.
 *
 * Keep in mind that several mounts may be running in parallel.  Starting
 * the search one past where the previous search terminated is both a
 * micro-optimization and a defense against returning the same fsid to
 * different mounts.
 */
void
vfs_getnewfsid(struct mount *mp)
{
        static uint16_t mntid_base;
        struct mount *nmp;
        fsid_t tfsid;
        int mtype;

        CTR2(KTR_VFS, "%s: mp %p", __func__, mp);
        mtx_lock(&mntid_mtx);
        mtype = mp->mnt_vfc->vfc_typenum;
        tfsid.val[1] = mtype;
        mtype = (mtype & 0xFF) << 24;
        for (;;) {
                tfsid.val[0] = makedev(255,
                    mtype | ((mntid_base & 0xFF00) << 8) | (mntid_base & 0xFF));
                mntid_base++;
                if ((nmp = vfs_getvfs(&tfsid)) == NULL)
                        break;
                vfs_rel(nmp);
        }
        mp->mnt_stat.f_fsid.val[0] = tfsid.val[0];
        mp->mnt_stat.f_fsid.val[1] = tfsid.val[1];
        mtx_unlock(&mntid_mtx);
}

/*
 * Knob to control the precision of file timestamps:
 *
 *   0 = seconds only; nanoseconds zeroed.
 *   1 = seconds and nanoseconds, accurate within 1/HZ.
 *   2 = seconds and nanoseconds, truncated to microseconds.
 * >=3 = seconds and nanoseconds, maximum precision.
 */
enum { TSP_SEC, TSP_HZ, TSP_USEC, TSP_NSEC };

static int timestamp_precision = TSP_USEC;
SYSCTL_INT(_vfs, OID_AUTO, timestamp_precision, CTLFLAG_RW,
    &timestamp_precision, 0, "File timestamp precision (0: seconds, "
    "1: sec + ns accurate to 1/HZ, 2: sec + ns truncated to us, "
    "3+: sec + ns (max. precision))");

/*
 * Get a current timestamp.
 */
void
vfs_timestamp(struct timespec *tsp)
{
        struct timeval tv;

        switch (timestamp_precision) {
        case TSP_SEC:
                tsp->tv_sec = time_second;
                tsp->tv_nsec = 0;
                break;
        case TSP_HZ:
                getnanotime(tsp);
                break;
        case TSP_USEC:
                microtime(&tv);
                TIMEVAL_TO_TIMESPEC(&tv, tsp);
                break;
        case TSP_NSEC:
        default:
                nanotime(tsp);
                break;
        }
}

/*
 * Set vnode attributes to VNOVAL
 */
void
vattr_null(struct vattr *vap)
{

        vap->va_type = VNON;
        vap->va_size = VNOVAL;
        vap->va_bytes = VNOVAL;
        vap->va_mode = VNOVAL;
        vap->va_nlink = VNOVAL;
        vap->va_uid = VNOVAL;
        vap->va_gid = VNOVAL;
        vap->va_fsid = VNOVAL;
        vap->va_fileid = VNOVAL;
        vap->va_blocksize = VNOVAL;
        vap->va_rdev = VNOVAL;
        vap->va_atime.tv_sec = VNOVAL;
        vap->va_atime.tv_nsec = VNOVAL;
        vap->va_mtime.tv_sec = VNOVAL;
        vap->va_mtime.tv_nsec = VNOVAL;
        vap->va_ctime.tv_sec = VNOVAL;
        vap->va_ctime.tv_nsec = VNOVAL;
        vap->va_birthtime.tv_sec = VNOVAL;
        vap->va_birthtime.tv_nsec = VNOVAL;
        vap->va_flags = VNOVAL;
        vap->va_gen = VNOVAL;
        vap->va_vaflags = 0;
}

/*
 * Try to reduce the total number of vnodes.
 *
 * This routine (and its user) are buggy in at least the following ways:
 * - all parameters were picked years ago when RAM sizes were significantly
 *   smaller
 * - it can pick vnodes based on pages used by the vm object, but filesystems
 *   like ZFS don't use it making the pick broken
 * - since ZFS has its own aging policy it gets partially combated by this one
 * - a dedicated method should be provided for filesystems to let them decide
 *   whether the vnode should be recycled
 *
 * This routine is called when we have too many vnodes.  It attempts
 * to free <count> vnodes and will potentially free vnodes that still
 * have VM backing store (VM backing store is typically the cause
 * of a vnode blowout so we want to do this).  Therefore, this operation
 * is not considered cheap.
 *
 * A number of conditions may prevent a vnode from being reclaimed.
 * the buffer cache may have references on the vnode, a directory
 * vnode may still have references due to the namei cache representing
 * underlying files, or the vnode may be in active use.   It is not
 * desirable to reuse such vnodes.  These conditions may cause the
 * number of vnodes to reach some minimum value regardless of what
 * you set kern.maxvnodes to.  Do not set kern.maxvnodes too low.
 *
 * @param reclaim_nc_src Only reclaim directories with outgoing namecache
 *                       entries if this argument is strue
 * @param trigger        Only reclaim vnodes with fewer than this many resident
 *                       pages.
 * @param target         How many vnodes to reclaim.
 * @return               The number of vnodes that were reclaimed.
 */
static int
vlrureclaim(bool reclaim_nc_src, int trigger, u_long target)
{
        struct vnode *vp, *mvp;
        struct mount *mp;
        u_long done;
        bool retried;

        mtx_assert(&vnode_list_mtx, MA_OWNED);

        retried = false;
        done = 0;

        mvp = vnode_list_reclaim_marker;
restart:
        vp = mvp;
        while (done < target) {
                vp = TAILQ_NEXT(vp, v_vnodelist);
                if (__predict_false(vp == NULL))
                        break;

                if (__predict_false(vp->v_type == VMARKER))
                        continue;

                /*
                 * If it's been deconstructed already, it's still
                 * referenced, or it exceeds the trigger, skip it.
                 * Also skip free vnodes.  We are trying to make space
                 * to expand the free list, not reduce it.
                 */
                if (vp->v_usecount > 0 || vp->v_holdcnt == 0 ||
                    (!reclaim_nc_src && !LIST_EMPTY(&vp->v_cache_src)))
                        goto next_iter;

                if (vp->v_type == VBAD || vp->v_type == VNON)
                        goto next_iter;

                if (!VI_TRYLOCK(vp))
                        goto next_iter;

                if (vp->v_usecount > 0 || vp->v_holdcnt == 0 ||
                    (!reclaim_nc_src && !LIST_EMPTY(&vp->v_cache_src)) ||
                    vp->v_type == VBAD || vp->v_type == VNON ||
                    (vp->v_object != NULL &&
                    vp->v_object->resident_page_count > trigger)) {
                        VI_UNLOCK(vp);
                        goto next_iter;
                }
                vholdl(vp);
                VI_UNLOCK(vp);
                TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                TAILQ_INSERT_AFTER(&vnode_list, vp, mvp, v_vnodelist);
                mtx_unlock(&vnode_list_mtx);

                if (vn_start_write(vp, &mp, V_NOWAIT) != 0) {
                        vdrop(vp);
                        goto next_iter_unlocked;
                }
                if (VOP_LOCK(vp, LK_EXCLUSIVE|LK_NOWAIT) != 0) {
                        vdrop(vp);
                        vn_finished_write(mp);
                        goto next_iter_unlocked;
                }

                VI_LOCK(vp);
                if (vp->v_usecount > 0 ||
                    (!reclaim_nc_src && !LIST_EMPTY(&vp->v_cache_src)) ||
                    (vp->v_object != NULL &&
                    vp->v_object->resident_page_count > trigger)) {
                        VOP_UNLOCK(vp);
                        vdropl(vp);
                        vn_finished_write(mp);
                        goto next_iter_unlocked;
                }
                counter_u64_add(recycles_count, 1);
                vgonel(vp);
                VOP_UNLOCK(vp);
                vdropl(vp);
                vn_finished_write(mp);
                done++;
next_iter_unlocked:
                if (should_yield())
                        kern_yield(PRI_USER);
                mtx_lock(&vnode_list_mtx);
                goto restart;
next_iter:
                MPASS(vp->v_type != VMARKER);
                if (!should_yield())
                        continue;
                TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                TAILQ_INSERT_AFTER(&vnode_list, vp, mvp, v_vnodelist);
                mtx_unlock(&vnode_list_mtx);
                kern_yield(PRI_USER);
                mtx_lock(&vnode_list_mtx);
                goto restart;
        }
        if (done == 0 && !retried) {
                TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                TAILQ_INSERT_HEAD(&vnode_list, mvp, v_vnodelist);
                retried = true;
                goto restart;
        }
        return (done);
}

static int max_vnlru_free = 10000; /* limit on vnode free requests per call */
SYSCTL_INT(_debug, OID_AUTO, max_vnlru_free, CTLFLAG_RW, &max_vnlru_free,
    0,
    "limit on vnode free requests per call to the vnlru_free routine");

/*
 * Attempt to reduce the free list by the requested amount.
 */
static int
vnlru_free_locked(int count, struct vfsops *mnt_op)
{
        struct vnode *vp, *mvp;
        struct mount *mp;
        int ocount;

        mtx_assert(&vnode_list_mtx, MA_OWNED);
        if (count > max_vnlru_free)
                count = max_vnlru_free;
        ocount = count;
        mvp = vnode_list_free_marker;
restart:
        vp = mvp;
        while (count > 0) {
                vp = TAILQ_NEXT(vp, v_vnodelist);
                if (__predict_false(vp == NULL)) {
                        TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                        TAILQ_INSERT_TAIL(&vnode_list, mvp, v_vnodelist);
                        break;
                }
                if (__predict_false(vp->v_type == VMARKER))
                        continue;

                /*
                 * Don't recycle if our vnode is from different type
                 * of mount point.  Note that mp is type-safe, the
                 * check does not reach unmapped address even if
                 * vnode is reclaimed.
                 * Don't recycle if we can't get the interlock without
                 * blocking.
                 */
                if (vp->v_holdcnt > 0 || (mnt_op != NULL && (mp = vp->v_mount) != NULL &&
                    mp->mnt_op != mnt_op) || !VI_TRYLOCK(vp)) {
                        continue;
                }
                TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                TAILQ_INSERT_AFTER(&vnode_list, vp, mvp, v_vnodelist);
                if (__predict_false(vp->v_type == VBAD || vp->v_type == VNON)) {
                        VI_UNLOCK(vp);
                        continue;
                }
                vholdl(vp);
                count--;
                mtx_unlock(&vnode_list_mtx);
                VI_UNLOCK(vp);
                vtryrecycle(vp);
                vdrop(vp);
                mtx_lock(&vnode_list_mtx);
                goto restart;
        }
        return (ocount - count);
}

void
vnlru_free(int count, struct vfsops *mnt_op)
{

        mtx_lock(&vnode_list_mtx);
        vnlru_free_locked(count, mnt_op);
        mtx_unlock(&vnode_list_mtx);
}

static void
vnlru_recalc(void)
{

        mtx_assert(&vnode_list_mtx, MA_OWNED);
        gapvnodes = imax(desiredvnodes - wantfreevnodes, 100);
        vhiwat = gapvnodes / 11; /* 9% -- just under the 10% in vlrureclaim() */
        vlowat = vhiwat / 2;
}

/*
 * Attempt to recycle vnodes in a context that is always safe to block.
 * Calling vlrurecycle() from the bowels of filesystem code has some
 * interesting deadlock problems.
 */
static struct proc *vnlruproc;
static int vnlruproc_sig;

/*
 * The main freevnodes counter is only updated when threads requeue their vnode
 * batches. CPUs are conditionally walked to compute a more accurate total.
 *
 * Limit how much of a slop are we willing to tolerate. Note: the actual value
 * at any given moment can still exceed slop, but it should not be by significant
 * margin in practice.
 */
#define VNLRU_FREEVNODES_SLOP 128

static u_long
vnlru_read_freevnodes(void)
{
        struct vdbatch *vd;
        long slop;
        int cpu;

        mtx_assert(&vnode_list_mtx, MA_OWNED);
        if (freevnodes > freevnodes_old)
                slop = freevnodes - freevnodes_old;
        else
                slop = freevnodes_old - freevnodes;
        if (slop < VNLRU_FREEVNODES_SLOP)
                return (freevnodes >= 0 ? freevnodes : 0);
        freevnodes_old = freevnodes;
        CPU_FOREACH(cpu) {
                vd = DPCPU_ID_PTR((cpu), vd);
                freevnodes_old += vd->freevnodes;
        }
        return (freevnodes_old >= 0 ? freevnodes_old : 0);
}

static bool
vnlru_under(u_long rnumvnodes, u_long limit)
{
        u_long rfreevnodes, space;

        if (__predict_false(rnumvnodes > desiredvnodes))
                return (true);

        space = desiredvnodes - rnumvnodes;
        if (space < limit) {
                rfreevnodes = vnlru_read_freevnodes();
                if (rfreevnodes > wantfreevnodes)
                        space += rfreevnodes - wantfreevnodes;
        }
        return (space < limit);
}

static bool
vnlru_under_unlocked(u_long rnumvnodes, u_long limit)
{
        long rfreevnodes, space;

        if (__predict_false(rnumvnodes > desiredvnodes))
                return (true);

        space = desiredvnodes - rnumvnodes;
        if (space < limit) {
                rfreevnodes = atomic_load_long(&freevnodes);
                if (rfreevnodes > wantfreevnodes)
                        space += rfreevnodes - wantfreevnodes;
        }
        return (space < limit);
}

static void
vnlru_kick(void)
{

        mtx_assert(&vnode_list_mtx, MA_OWNED);
        if (vnlruproc_sig == 0) {
                vnlruproc_sig = 1;
                wakeup(vnlruproc);
        }
}

static void
vnlru_proc(void)
{
        u_long rnumvnodes, rfreevnodes, target;
        unsigned long onumvnodes;
        int done, force, trigger, usevnodes;
        bool reclaim_nc_src, want_reread;

        EVENTHANDLER_REGISTER(shutdown_pre_sync, kproc_shutdown, vnlruproc,
            SHUTDOWN_PRI_FIRST);

        force = 0;
        want_reread = false;
        for (;;) {
                kproc_suspend_check(vnlruproc);
                mtx_lock(&vnode_list_mtx);
                rnumvnodes = atomic_load_long(&numvnodes);

                if (want_reread) {
                        force = vnlru_under(numvnodes, vhiwat) ? 1 : 0;
                        want_reread = false;
                }

                /*
                 * If numvnodes is too large (due to desiredvnodes being
                 * adjusted using its sysctl, or emergency growth), first
                 * try to reduce it by discarding from the free list.
                 */
                if (rnumvnodes > desiredvnodes) {
                        vnlru_free_locked(rnumvnodes - desiredvnodes, NULL);
                        rnumvnodes = atomic_load_long(&numvnodes);
                }
                /*
                 * Sleep if the vnode cache is in a good state.  This is
                 * when it is not over-full and has space for about a 4%
                 * or 9% expansion (by growing its size or inexcessively
                 * reducing its free list).  Otherwise, try to reclaim
                 * space for a 10% expansion.
                 */
                if (vstir && force == 0) {
                        force = 1;
                        vstir = 0;
                }
                if (force == 0 && !vnlru_under(rnumvnodes, vlowat)) {
                        vnlruproc_sig = 0;
                        wakeup(&vnlruproc_sig);
                        msleep(vnlruproc, &vnode_list_mtx,
                            PVFS|PDROP, "vlruwt", hz);
                        continue;
                }
                rfreevnodes = vnlru_read_freevnodes();

                onumvnodes = rnumvnodes;
                /*
                 * Calculate parameters for recycling.  These are the same
                 * throughout the loop to give some semblance of fairness.
                 * The trigger point is to avoid recycling vnodes with lots
                 * of resident pages.  We aren't trying to free memory; we
                 * are trying to recycle or at least free vnodes.
                 */
                if (rnumvnodes <= desiredvnodes)
                        usevnodes = rnumvnodes - rfreevnodes;
                else
                        usevnodes = rnumvnodes;
                if (usevnodes <= 0)
                        usevnodes = 1;
                /*
                 * The trigger value is is chosen to give a conservatively
                 * large value to ensure that it alone doesn't prevent
                 * making progress.  The value can easily be so large that
                 * it is effectively infinite in some congested and
                 * misconfigured cases, and this is necessary.  Normally
                 * it is about 8 to 100 (pages), which is quite large.
                 */
                trigger = vm_cnt.v_page_count * 2 / usevnodes;
                if (force < 2)
                        trigger = vsmalltrigger;
                reclaim_nc_src = force >= 3;
                target = rnumvnodes * (int64_t)gapvnodes / imax(desiredvnodes, 1);
                target = target / 10 + 1;
                done = vlrureclaim(reclaim_nc_src, trigger, target);
                mtx_unlock(&vnode_list_mtx);
                if (onumvnodes > desiredvnodes && numvnodes <= desiredvnodes)
                        uma_reclaim(UMA_RECLAIM_DRAIN);
                if (done == 0) {
                        if (force == 0 || force == 1) {
                                force = 2;
                                continue;
                        }
                        if (force == 2) {
                                force = 3;
                                continue;
                        }
                        want_reread = true;
                        force = 0;
                        vnlru_nowhere++;
                        tsleep(vnlruproc, PPAUSE, "vlrup", hz * 3);
                } else {
                        want_reread = true;
                        kern_yield(PRI_USER);
                }
        }
}

static struct kproc_desc vnlru_kp = {
        "vnlru",
        vnlru_proc,
        &vnlruproc
};
SYSINIT(vnlru, SI_SUB_KTHREAD_UPDATE, SI_ORDER_FIRST, kproc_start,
    &vnlru_kp);
 
/*
 * Routines having to do with the management of the vnode table.
 */

/*
 * Try to recycle a freed vnode.  We abort if anyone picks up a reference
 * before we actually vgone().  This function must be called with the vnode
 * held to prevent the vnode from being returned to the free list midway
 * through vgone().
 */
static int
vtryrecycle(struct vnode *vp)
{
        struct mount *vnmp;

        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        VNASSERT(vp->v_holdcnt, vp,
            ("vtryrecycle: Recycling vp %p without a reference.", vp));
        /*
         * This vnode may found and locked via some other list, if so we
         * can't recycle it yet.
         */
        if (VOP_LOCK(vp, LK_EXCLUSIVE | LK_NOWAIT) != 0) {
                CTR2(KTR_VFS,
                    "%s: impossible to recycle, vp %p lock is already held",
                    __func__, vp);
                return (EWOULDBLOCK);
        }
        /*
         * Don't recycle if its filesystem is being suspended.
         */
        if (vn_start_write(vp, &vnmp, V_NOWAIT) != 0) {
                VOP_UNLOCK(vp);
                CTR2(KTR_VFS,
                    "%s: impossible to recycle, cannot start the write for %p",
                    __func__, vp);
                return (EBUSY);
        }
        /*
         * If we got this far, we need to acquire the interlock and see if
         * anyone picked up this vnode from another list.  If not, we will
         * mark it with DOOMED via vgonel() so that anyone who does find it
         * will skip over it.
         */
        VI_LOCK(vp);
        if (vp->v_usecount) {
                VOP_UNLOCK(vp);
                VI_UNLOCK(vp);
                vn_finished_write(vnmp);
                CTR2(KTR_VFS,
                    "%s: impossible to recycle, %p is already referenced",
                    __func__, vp);
                return (EBUSY);
        }
        if (!VN_IS_DOOMED(vp)) {
                counter_u64_add(recycles_free_count, 1);
                vgonel(vp);
        }
        VOP_UNLOCK(vp);
        VI_UNLOCK(vp);
        vn_finished_write(vnmp);
        return (0);
}

/*
 * Allocate a new vnode.
 *
 * The operation never returns an error. Returning an error was disabled
 * in r145385 (dated 2005) with the following comment:
 *
 * XXX Not all VFS_VGET/ffs_vget callers check returns.
 *
 * Given the age of this commit (almost 15 years at the time of writing this
 * comment) restoring the ability to fail requires a significant audit of
 * all codepaths.
 *
 * The routine can try to free a vnode or stall for up to 1 second waiting for
 * vnlru to clear things up, but ultimately always performs a M_WAITOK allocation.
 */
static u_long vn_alloc_cyclecount;

static struct vnode * __noinline
vn_alloc_hard(struct mount *mp)
{
        u_long rnumvnodes, rfreevnodes;

        mtx_lock(&vnode_list_mtx);
        rnumvnodes = atomic_load_long(&numvnodes);
        if (rnumvnodes + 1 < desiredvnodes) {
                vn_alloc_cyclecount = 0;
                goto alloc;
        }
        rfreevnodes = vnlru_read_freevnodes();
        if (vn_alloc_cyclecount++ >= rfreevnodes) {
                vn_alloc_cyclecount = 0;
                vstir = 1;
        }
        /*
         * Grow the vnode cache if it will not be above its target max
         * after growing.  Otherwise, if the free list is nonempty, try
         * to reclaim 1 item from it before growing the cache (possibly
         * above its target max if the reclamation failed or is delayed).
         * Otherwise, wait for some space.  In all cases, schedule
         * vnlru_proc() if we are getting short of space.  The watermarks
         * should be chosen so that we never wait or even reclaim from
         * the free list to below its target minimum.
         */
        if (vnlru_free_locked(1, NULL) > 0)
                goto alloc;
        if (mp == NULL || (mp->mnt_kern_flag & MNTK_SUSPEND) == 0) {
                /*
                 * Wait for space for a new vnode.
                 */
                vnlru_kick();
                msleep(&vnlruproc_sig, &vnode_list_mtx, PVFS, "vlruwk", hz);
                if (atomic_load_long(&numvnodes) + 1 > desiredvnodes &&
                    vnlru_read_freevnodes() > 1)
                        vnlru_free_locked(1, NULL);
        }
alloc:
        rnumvnodes = atomic_fetchadd_long(&numvnodes, 1) + 1;
        if (vnlru_under(rnumvnodes, vlowat))
                vnlru_kick();
        mtx_unlock(&vnode_list_mtx);
        return (uma_zalloc(vnode_zone, M_WAITOK));
}

static struct vnode *
vn_alloc(struct mount *mp)
{
        u_long rnumvnodes;

        if (__predict_false(vn_alloc_cyclecount != 0))
                return (vn_alloc_hard(mp));
        rnumvnodes = atomic_fetchadd_long(&numvnodes, 1) + 1;
        if (__predict_false(vnlru_under_unlocked(rnumvnodes, vlowat))) {
                atomic_subtract_long(&numvnodes, 1);
                return (vn_alloc_hard(mp));
        }

        return (uma_zalloc(vnode_zone, M_WAITOK));
}

static void
vn_free(struct vnode *vp)
{

        atomic_subtract_long(&numvnodes, 1);
        uma_zfree(vnode_zone, vp);
}

/*
 * Return the next vnode from the free list.
 */
int
getnewvnode(const char *tag, struct mount *mp, struct vop_vector *vops,
    struct vnode **vpp)
{
        struct vnode *vp;
        struct thread *td;
        struct lock_object *lo;

        CTR3(KTR_VFS, "%s: mp %p with tag %s", __func__, mp, tag);

        KASSERT(vops->registered,
            ("%s: not registered vector op %p\n", __func__, vops));

        td = curthread;
        if (td->td_vp_reserved != NULL) {
                vp = td->td_vp_reserved;
                td->td_vp_reserved = NULL;
        } else {
                vp = vn_alloc(mp);
        }
        counter_u64_add(vnodes_created, 1);
        /*
         * Locks are given the generic name "vnode" when created.
         * Follow the historic practice of using the filesystem
         * name when they allocated, e.g., "zfs", "ufs", "nfs, etc.
         *
         * Locks live in a witness group keyed on their name. Thus,
         * when a lock is renamed, it must also move from the witness
         * group of its old name to the witness group of its new name.
         *
         * The change only needs to be made when the vnode moves
         * from one filesystem type to another. We ensure that each
         * filesystem use a single static name pointer for its tag so
         * that we can compare pointers rather than doing a strcmp().
         */
        lo = &vp->v_vnlock->lock_object;
#ifdef WITNESS
        if (lo->lo_name != tag) {
#endif
                lo->lo_name = tag;
#ifdef WITNESS
                WITNESS_DESTROY(lo);
                WITNESS_INIT(lo, tag);
        }
#endif
        /*
         * By default, don't allow shared locks unless filesystems opt-in.
         */
        vp->v_vnlock->lock_object.lo_flags |= LK_NOSHARE;
        /*
         * Finalize various vnode identity bits.
         */
        KASSERT(vp->v_object == NULL, ("stale v_object %p", vp));
        KASSERT(vp->v_lockf == NULL, ("stale v_lockf %p", vp));
        KASSERT(vp->v_pollinfo == NULL, ("stale v_pollinfo %p", vp));
        vp->v_type = VNON;
        vp->v_op = vops;
        v_init_counters(vp);
        vp->v_bufobj.bo_ops = &buf_ops_bio;
#ifdef DIAGNOSTIC
        if (mp == NULL && vops != &dead_vnodeops)
                printf("NULL mp in getnewvnode(9), tag %s\n", tag);
#endif
#ifdef MAC
        mac_vnode_init(vp);
        if (mp != NULL && (mp->mnt_flag & MNT_MULTILABEL) == 0)
                mac_vnode_associate_singlelabel(mp, vp);
#endif
        if (mp != NULL) {
                vp->v_bufobj.bo_bsize = mp->mnt_stat.f_iosize;
                if ((mp->mnt_kern_flag & MNTK_NOKNOTE) != 0)
                        vp->v_vflag |= VV_NOKNOTE;
        }

        /*
         * For the filesystems which do not use vfs_hash_insert(),
         * still initialize v_hash to have vfs_hash_index() useful.
         * E.g., nullfs uses vfs_hash_index() on the lower vnode for
         * its own hashing.
         */
        vp->v_hash = (uintptr_t)vp >> vnsz2log;

        *vpp = vp;
        return (0);
}

void
getnewvnode_reserve(void)
{
        struct thread *td;

        td = curthread;
        MPASS(td->td_vp_reserved == NULL);
        td->td_vp_reserved = vn_alloc(NULL);
}

void
getnewvnode_drop_reserve(void)
{
        struct thread *td;

        td = curthread;
        if (td->td_vp_reserved != NULL) {
                vn_free(td->td_vp_reserved);
                td->td_vp_reserved = NULL;
        }
}

static void
freevnode(struct vnode *vp)
{
        struct bufobj *bo;

        /*
         * The vnode has been marked for destruction, so free it.
         *
         * The vnode will be returned to the zone where it will
         * normally remain until it is needed for another vnode. We
         * need to cleanup (or verify that the cleanup has already
         * been done) any residual data left from its current use
         * so as not to contaminate the freshly allocated vnode.
         */
        CTR2(KTR_VFS, "%s: destroying the vnode %p", __func__, vp);
        bo = &vp->v_bufobj;
        VNASSERT(vp->v_data == NULL, vp, ("cleaned vnode isn't"));
        VNASSERT(vp->v_holdcnt == 0, vp, ("Non-zero hold count"));
        VNASSERT(vp->v_usecount == 0, vp, ("Non-zero use count"));
        VNASSERT(vp->v_writecount == 0, vp, ("Non-zero write count"));
        VNASSERT(bo->bo_numoutput == 0, vp, ("Clean vnode has pending I/O's"));
        VNASSERT(bo->bo_clean.bv_cnt == 0, vp, ("cleanbufcnt not 0"));
        VNASSERT(pctrie_is_empty(&bo->bo_clean.bv_root), vp,
            ("clean blk trie not empty"));
        VNASSERT(bo->bo_dirty.bv_cnt == 0, vp, ("dirtybufcnt not 0"));
        VNASSERT(pctrie_is_empty(&bo->bo_dirty.bv_root), vp,
            ("dirty blk trie not empty"));
        VNASSERT(TAILQ_EMPTY(&vp->v_cache_dst), vp, ("vp has namecache dst"));
        VNASSERT(LIST_EMPTY(&vp->v_cache_src), vp, ("vp has namecache src"));
        VNASSERT(vp->v_cache_dd == NULL, vp, ("vp has namecache for .."));
        VNASSERT(TAILQ_EMPTY(&vp->v_rl.rl_waiters), vp,
            ("Dangling rangelock waiters"));
        VI_UNLOCK(vp);
#ifdef MAC
        mac_vnode_destroy(vp);
#endif
        if (vp->v_pollinfo != NULL) {
                destroy_vpollinfo(vp->v_pollinfo);
                vp->v_pollinfo = NULL;
        }
#ifdef INVARIANTS
        /* XXX Elsewhere we detect an already freed vnode via NULL v_op. */
        vp->v_op = NULL;
#endif
        vp->v_mountedhere = NULL;
        vp->v_unpcb = NULL;
        vp->v_rdev = NULL;
        vp->v_fifoinfo = NULL;
        vp->v_lasta = vp->v_clen = vp->v_cstart = vp->v_lastw = 0;
        vp->v_irflag = 0;
        vp->v_iflag = 0;
        vp->v_vflag = 0;
        bo->bo_flag = 0;
        vn_free(vp);
}

/*
 * Delete from old mount point vnode list, if on one.
 */
static void
delmntque(struct vnode *vp)
{
        struct mount *mp;

        mp = vp->v_mount;
        if (mp == NULL)
                return;
        MNT_ILOCK(mp);
        VI_LOCK(vp);
        if (vp->v_mflag & VMP_LAZYLIST) {
                mtx_lock(&mp->mnt_listmtx);
                if (vp->v_mflag & VMP_LAZYLIST) {
                        vp->v_mflag &= ~VMP_LAZYLIST;
                        TAILQ_REMOVE(&mp->mnt_lazyvnodelist, vp, v_lazylist);
                        mp->mnt_lazyvnodelistsize--;
                }
                mtx_unlock(&mp->mnt_listmtx);
        }
        vp->v_mount = NULL;
        VI_UNLOCK(vp);
        VNASSERT(mp->mnt_nvnodelistsize > 0, vp,
                ("bad mount point vnode list size"));
        TAILQ_REMOVE(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
        mp->mnt_nvnodelistsize--;
        MNT_REL(mp);
        MNT_IUNLOCK(mp);
}

static void
insmntque_stddtr(struct vnode *vp, void *dtr_arg)
{

        vp->v_data = NULL;
        vp->v_op = &dead_vnodeops;
        vgone(vp);
        vput(vp);
}

/*
 * Insert into list of vnodes for the new mount point, if available.
 */
int
insmntque1(struct vnode *vp, struct mount *mp,
        void (*dtr)(struct vnode *, void *), void *dtr_arg)
{

        KASSERT(vp->v_mount == NULL,
                ("insmntque: vnode already on per mount vnode list"));
        VNASSERT(mp != NULL, vp, ("Don't call insmntque(foo, NULL)"));
        ASSERT_VOP_ELOCKED(vp, "insmntque: non-locked vp");

        /*
         * We acquire the vnode interlock early to ensure that the
         * vnode cannot be recycled by another process releasing a
         * holdcnt on it before we get it on both the vnode list
         * and the active vnode list. The mount mutex protects only
         * manipulation of the vnode list and the vnode freelist
         * mutex protects only manipulation of the active vnode list.
         * Hence the need to hold the vnode interlock throughout.
         */
        MNT_ILOCK(mp);
        VI_LOCK(vp);
        if (((mp->mnt_kern_flag & MNTK_UNMOUNT) != 0 &&
            ((mp->mnt_kern_flag & MNTK_UNMOUNTF) != 0 ||
            mp->mnt_nvnodelistsize == 0)) &&
            (vp->v_vflag & VV_FORCEINSMQ) == 0) {
                VI_UNLOCK(vp);
                MNT_IUNLOCK(mp);
                if (dtr != NULL)
                        dtr(vp, dtr_arg);
                return (EBUSY);
        }
        vp->v_mount = mp;
        MNT_REF(mp);
        TAILQ_INSERT_TAIL(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
        VNASSERT(mp->mnt_nvnodelistsize >= 0, vp,
                ("neg mount point vnode list size"));
        mp->mnt_nvnodelistsize++;
        VI_UNLOCK(vp);
        MNT_IUNLOCK(mp);
        return (0);
}

int
insmntque(struct vnode *vp, struct mount *mp)
{

        return (insmntque1(vp, mp, insmntque_stddtr, NULL));
}

/*
 * Flush out and invalidate all buffers associated with a bufobj
 * Called with the underlying object locked.
 */
int
bufobj_invalbuf(struct bufobj *bo, int flags, int slpflag, int slptimeo)
{
        int error;

        BO_LOCK(bo);
        if (flags & V_SAVE) {
                error = bufobj_wwait(bo, slpflag, slptimeo);
                if (error) {
                        BO_UNLOCK(bo);
                        return (error);
                }
                if (bo->bo_dirty.bv_cnt > 0) {
                        BO_UNLOCK(bo);
                        if ((error = BO_SYNC(bo, MNT_WAIT)) != 0)
                                return (error);
                        /*
                         * XXX We could save a lock/unlock if this was only
                         * enabled under INVARIANTS
                         */
                        BO_LOCK(bo);
                        if (bo->bo_numoutput > 0 || bo->bo_dirty.bv_cnt > 0)
                                panic("vinvalbuf: dirty bufs");
                }
        }
        /*
         * If you alter this loop please notice that interlock is dropped and
         * reacquired in flushbuflist.  Special care is needed to ensure that
         * no race conditions occur from this.
         */
        do {
                error = flushbuflist(&bo->bo_clean,
                    flags, bo, slpflag, slptimeo);
                if (error == 0 && !(flags & V_CLEANONLY))
                        error = flushbuflist(&bo->bo_dirty,
                            flags, bo, slpflag, slptimeo);
                if (error != 0 && error != EAGAIN) {
                        BO_UNLOCK(bo);
                        return (error);
                }
        } while (error != 0);

        /*
         * Wait for I/O to complete.  XXX needs cleaning up.  The vnode can
         * have write I/O in-progress but if there is a VM object then the
         * VM object can also have read-I/O in-progress.
         */
        do {
                bufobj_wwait(bo, 0, 0);
                if ((flags & V_VMIO) == 0 && bo->bo_object != NULL) {
                        BO_UNLOCK(bo);
                        vm_object_pip_wait_unlocked(bo->bo_object, "bovlbx");
                        BO_LOCK(bo);
                }
        } while (bo->bo_numoutput > 0);
        BO_UNLOCK(bo);

        /*
         * Destroy the copy in the VM cache, too.
         */
        if (bo->bo_object != NULL &&
            (flags & (V_ALT | V_NORMAL | V_CLEANONLY | V_VMIO)) == 0) {
                VM_OBJECT_WLOCK(bo->bo_object);
                vm_object_page_remove(bo->bo_object, 0, 0, (flags & V_SAVE) ?
                    OBJPR_CLEANONLY : 0);
                VM_OBJECT_WUNLOCK(bo->bo_object);
        }

#ifdef INVARIANTS
        BO_LOCK(bo);
        if ((flags & (V_ALT | V_NORMAL | V_CLEANONLY | V_VMIO |
            V_ALLOWCLEAN)) == 0 && (bo->bo_dirty.bv_cnt > 0 ||
            bo->bo_clean.bv_cnt > 0))
                panic("vinvalbuf: flush failed");
        if ((flags & (V_ALT | V_NORMAL | V_CLEANONLY | V_VMIO)) == 0 &&
            bo->bo_dirty.bv_cnt > 0)
                panic("vinvalbuf: flush dirty failed");
        BO_UNLOCK(bo);
#endif
        return (0);
}

/*
 * Flush out and invalidate all buffers associated with a vnode.
 * Called with the underlying object locked.
 */
int
vinvalbuf(struct vnode *vp, int flags, int slpflag, int slptimeo)
{

        CTR3(KTR_VFS, "%s: vp %p with flags %d", __func__, vp, flags);
        ASSERT_VOP_LOCKED(vp, "vinvalbuf");
        if (vp->v_object != NULL && vp->v_object->handle != vp)
                return (0);
        return (bufobj_invalbuf(&vp->v_bufobj, flags, slpflag, slptimeo));
}

/*
 * Flush out buffers on the specified list.
 *
 */
static int
flushbuflist(struct bufv *bufv, int flags, struct bufobj *bo, int slpflag,
    int slptimeo)
{
        struct buf *bp, *nbp;
        int retval, error;
        daddr_t lblkno;
        b_xflags_t xflags;

        ASSERT_BO_WLOCKED(bo);

        retval = 0;
        TAILQ_FOREACH_SAFE(bp, &bufv->bv_hd, b_bobufs, nbp) {
                /*
                 * If we are flushing both V_NORMAL and V_ALT buffers then
                 * do not skip any buffers. If we are flushing only V_NORMAL
                 * buffers then skip buffers marked as BX_ALTDATA. If we are
                 * flushing only V_ALT buffers then skip buffers not marked
                 * as BX_ALTDATA.
                 */
                if (((flags & (V_NORMAL | V_ALT)) != (V_NORMAL | V_ALT)) &&
                   (((flags & V_NORMAL) && (bp->b_xflags & BX_ALTDATA) != 0) ||
                    ((flags & V_ALT) && (bp->b_xflags & BX_ALTDATA) == 0))) {
                        continue;
                }
                if (nbp != NULL) {
                        lblkno = nbp->b_lblkno;
                        xflags = nbp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN);
                }
                retval = EAGAIN;
                error = BUF_TIMELOCK(bp,
                    LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK, BO_LOCKPTR(bo),
                    "flushbuf", slpflag, slptimeo);
                if (error) {
                        BO_LOCK(bo);
                        return (error != ENOLCK ? error : EAGAIN);
                }
                KASSERT(bp->b_bufobj == bo,
                    ("bp %p wrong b_bufobj %p should be %p",
                    bp, bp->b_bufobj, bo));
                /*
                 * XXX Since there are no node locks for NFS, I
                 * believe there is a slight chance that a delayed
                 * write will occur while sleeping just above, so
                 * check for it.
                 */
                if (((bp->b_flags & (B_DELWRI | B_INVAL)) == B_DELWRI) &&
                    (flags & V_SAVE)) {
                        bremfree(bp);
                        bp->b_flags |= B_ASYNC;
                        bwrite(bp);
                        BO_LOCK(bo);
                        return (EAGAIN);        /* XXX: why not loop ? */
                }
                bremfree(bp);
                bp->b_flags |= (B_INVAL | B_RELBUF);
                bp->b_flags &= ~B_ASYNC;
                brelse(bp);
                BO_LOCK(bo);
                if (nbp == NULL)
                        break;
                nbp = gbincore(bo, lblkno);
                if (nbp == NULL || (nbp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN))
                    != xflags)
                        break;                  /* nbp invalid */
        }
        return (retval);
}

int
bnoreuselist(struct bufv *bufv, struct bufobj *bo, daddr_t startn, daddr_t endn)
{
        struct buf *bp;
        int error;
        daddr_t lblkno;

        ASSERT_BO_LOCKED(bo);

        for (lblkno = startn;;) {
again:
                bp = BUF_PCTRIE_LOOKUP_GE(&bufv->bv_root, lblkno);
                if (bp == NULL || bp->b_lblkno >= endn ||
                    bp->b_lblkno < startn)
                        break;
                error = BUF_TIMELOCK(bp, LK_EXCLUSIVE | LK_SLEEPFAIL |
                    LK_INTERLOCK, BO_LOCKPTR(bo), "brlsfl", 0, 0);
                if (error != 0) {
                        BO_RLOCK(bo);
                        if (error == ENOLCK)
                                goto again;
                        return (error);
                }
                KASSERT(bp->b_bufobj == bo,
                    ("bp %p wrong b_bufobj %p should be %p",
                    bp, bp->b_bufobj, bo));
                lblkno = bp->b_lblkno + 1;
                if ((bp->b_flags & B_MANAGED) == 0)
                        bremfree(bp);
                bp->b_flags |= B_RELBUF;
                /*
                 * In the VMIO case, use the B_NOREUSE flag to hint that the
                 * pages backing each buffer in the range are unlikely to be
                 * reused.  Dirty buffers will have the hint applied once
                 * they've been written.
                 */
                if ((bp->b_flags & B_VMIO) != 0)
                        bp->b_flags |= B_NOREUSE;
                brelse(bp);
                BO_RLOCK(bo);
        }
        return (0);
}

/*
 * Truncate a file's buffer and pages to a specified length.  This
 * is in lieu of the old vinvalbuf mechanism, which performed unneeded
 * sync activity.
 */
int
vtruncbuf(struct vnode *vp, off_t length, int blksize)
{
        struct buf *bp, *nbp;
        struct bufobj *bo;
        daddr_t startlbn;

        CTR4(KTR_VFS, "%s: vp %p with block %d:%ju", __func__,
            vp, blksize, (uintmax_t)length);

        /*
         * Round up to the *next* lbn.
         */
        startlbn = howmany(length, blksize);

        ASSERT_VOP_LOCKED(vp, "vtruncbuf");

        bo = &vp->v_bufobj;
restart_unlocked:
        BO_LOCK(bo);

        while (v_inval_buf_range_locked(vp, bo, startlbn, INT64_MAX) == EAGAIN)
                ;

        if (length > 0) {
restartsync:
                TAILQ_FOREACH_SAFE(bp, &bo->bo_dirty.bv_hd, b_bobufs, nbp) {
                        if (bp->b_lblkno > 0)
                                continue;
                        /*
                         * Since we hold the vnode lock this should only
                         * fail if we're racing with the buf daemon.
                         */
                        if (BUF_LOCK(bp,
                            LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                            BO_LOCKPTR(bo)) == ENOLCK)
                                goto restart_unlocked;

                        VNASSERT((bp->b_flags & B_DELWRI), vp,
                            ("buf(%p) on dirty queue without DELWRI", bp));

                        bremfree(bp);
                        bawrite(bp);
                        BO_LOCK(bo);
                        goto restartsync;
                }
        }

        bufobj_wwait(bo, 0, 0);
        BO_UNLOCK(bo);
        vnode_pager_setsize(vp, length);

        return (0);
}

/*
 * Invalidate the cached pages of a file's buffer within the range of block
 * numbers [startlbn, endlbn).
 */
void
v_inval_buf_range(struct vnode *vp, daddr_t startlbn, daddr_t endlbn,
    int blksize)
{
        struct bufobj *bo;
        off_t start, end;

        ASSERT_VOP_LOCKED(vp, "v_inval_buf_range");

        start = blksize * startlbn;
        end = blksize * endlbn;

        bo = &vp->v_bufobj;
        BO_LOCK(bo);
        MPASS(blksize == bo->bo_bsize);

        while (v_inval_buf_range_locked(vp, bo, startlbn, endlbn) == EAGAIN)
                ;

        BO_UNLOCK(bo);
        vn_pages_remove(vp, OFF_TO_IDX(start), OFF_TO_IDX(end + PAGE_SIZE - 1));
}

static int
v_inval_buf_range_locked(struct vnode *vp, struct bufobj *bo,
    daddr_t startlbn, daddr_t endlbn)
{
        struct buf *bp, *nbp;
        bool anyfreed;

        ASSERT_VOP_LOCKED(vp, "v_inval_buf_range_locked");
        ASSERT_BO_LOCKED(bo);

        do {
                anyfreed = false;
                TAILQ_FOREACH_SAFE(bp, &bo->bo_clean.bv_hd, b_bobufs, nbp) {
                        if (bp->b_lblkno < startlbn || bp->b_lblkno >= endlbn)
                                continue;
                        if (BUF_LOCK(bp,
                            LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                            BO_LOCKPTR(bo)) == ENOLCK) {
                                BO_LOCK(bo);
                                return (EAGAIN);
                        }

                        bremfree(bp);
                        bp->b_flags |= B_INVAL | B_RELBUF;
                        bp->b_flags &= ~B_ASYNC;
                        brelse(bp);
                        anyfreed = true;

                        BO_LOCK(bo);
                        if (nbp != NULL &&
                            (((nbp->b_xflags & BX_VNCLEAN) == 0) ||
                            nbp->b_vp != vp ||
                            (nbp->b_flags & B_DELWRI) != 0))
                                return (EAGAIN);
                }

                TAILQ_FOREACH_SAFE(bp, &bo->bo_dirty.bv_hd, b_bobufs, nbp) {
                        if (bp->b_lblkno < startlbn || bp->b_lblkno >= endlbn)
                                continue;
                        if (BUF_LOCK(bp,
                            LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                            BO_LOCKPTR(bo)) == ENOLCK) {
                                BO_LOCK(bo);
                                return (EAGAIN);
                        }
                        bremfree(bp);
                        bp->b_flags |= B_INVAL | B_RELBUF;
                        bp->b_flags &= ~B_ASYNC;
                        brelse(bp);
                        anyfreed = true;

                        BO_LOCK(bo);
                        if (nbp != NULL &&
                            (((nbp->b_xflags & BX_VNDIRTY) == 0) ||
                            (nbp->b_vp != vp) ||
                            (nbp->b_flags & B_DELWRI) == 0))
                                return (EAGAIN);
                }
        } while (anyfreed);
        return (0);
}

static void
buf_vlist_remove(struct buf *bp)
{
        struct bufv *bv;

        KASSERT(bp->b_bufobj != NULL, ("No b_bufobj %p", bp));
        ASSERT_BO_WLOCKED(bp->b_bufobj);
        KASSERT((bp->b_xflags & (BX_VNDIRTY|BX_VNCLEAN)) !=
            (BX_VNDIRTY|BX_VNCLEAN),
            ("buf_vlist_remove: Buf %p is on two lists", bp));
        if (bp->b_xflags & BX_VNDIRTY)
                bv = &bp->b_bufobj->bo_dirty;
        else
                bv = &bp->b_bufobj->bo_clean;
        BUF_PCTRIE_REMOVE(&bv->bv_root, bp->b_lblkno);
        TAILQ_REMOVE(&bv->bv_hd, bp, b_bobufs);
        bv->bv_cnt--;
        bp->b_xflags &= ~(BX_VNDIRTY | BX_VNCLEAN);
}

/*
 * Add the buffer to the sorted clean or dirty block list.
 *
 * NOTE: xflags is passed as a constant, optimizing this inline function!
 */
static void
buf_vlist_add(struct buf *bp, struct bufobj *bo, b_xflags_t xflags)
{
        struct bufv *bv;
        struct buf *n;
        int error;

        ASSERT_BO_WLOCKED(bo);
        KASSERT((xflags & BX_VNDIRTY) == 0 || (bo->bo_flag & BO_DEAD) == 0,
            ("dead bo %p", bo));
        KASSERT((bp->b_xflags & (BX_VNDIRTY|BX_VNCLEAN)) == 0,
            ("buf_vlist_add: Buf %p has existing xflags %d", bp, bp->b_xflags));
        bp->b_xflags |= xflags;
        if (xflags & BX_VNDIRTY)
                bv = &bo->bo_dirty;
        else
                bv = &bo->bo_clean;

        /*
         * Keep the list ordered.  Optimize empty list insertion.  Assume
         * we tend to grow at the tail so lookup_le should usually be cheaper
         * than _ge. 
         */
        if (bv->bv_cnt == 0 ||
            bp->b_lblkno > TAILQ_LAST(&bv->bv_hd, buflists)->b_lblkno)
                TAILQ_INSERT_TAIL(&bv->bv_hd, bp, b_bobufs);
        else if ((n = BUF_PCTRIE_LOOKUP_LE(&bv->bv_root, bp->b_lblkno)) == NULL)
                TAILQ_INSERT_HEAD(&bv->bv_hd, bp, b_bobufs);
        else
                TAILQ_INSERT_AFTER(&bv->bv_hd, n, bp, b_bobufs);
        error = BUF_PCTRIE_INSERT(&bv->bv_root, bp);
        if (error)
                panic("buf_vlist_add:  Preallocated nodes insufficient.");
        bv->bv_cnt++;
}

/*
 * Look up a buffer using the buffer tries.
 */
struct buf *
gbincore(struct bufobj *bo, daddr_t lblkno)
{
        struct buf *bp;

        ASSERT_BO_LOCKED(bo);
        bp = BUF_PCTRIE_LOOKUP(&bo->bo_clean.bv_root, lblkno);
        if (bp != NULL)
                return (bp);
        return BUF_PCTRIE_LOOKUP(&bo->bo_dirty.bv_root, lblkno);
}

/*
 * Associate a buffer with a vnode.
 */
void
bgetvp(struct vnode *vp, struct buf *bp)
{
        struct bufobj *bo;

        bo = &vp->v_bufobj;
        ASSERT_BO_WLOCKED(bo);
        VNASSERT(bp->b_vp == NULL, bp->b_vp, ("bgetvp: not free"));

        CTR3(KTR_BUF, "bgetvp(%p) vp %p flags %X", bp, vp, bp->b_flags);
        VNASSERT((bp->b_xflags & (BX_VNDIRTY|BX_VNCLEAN)) == 0, vp,
            ("bgetvp: bp already attached! %p", bp));

        vhold(vp);
        bp->b_vp = vp;
        bp->b_bufobj = bo;
        /*
         * Insert onto list for new vnode.
         */
        buf_vlist_add(bp, bo, BX_VNCLEAN);
}

/*
 * Disassociate a buffer from a vnode.
 */
void
brelvp(struct buf *bp)
{
        struct bufobj *bo;
        struct vnode *vp;

        CTR3(KTR_BUF, "brelvp(%p) vp %p flags %X", bp, bp->b_vp, bp->b_flags);
        KASSERT(bp->b_vp != NULL, ("brelvp: NULL"));

        /*
         * Delete from old vnode list, if on one.
         */
        vp = bp->b_vp;          /* XXX */
        bo = bp->b_bufobj;
        BO_LOCK(bo);
        if (bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN))
                buf_vlist_remove(bp);
        else
                panic("brelvp: Buffer %p not on queue.", bp);
        if ((bo->bo_flag & BO_ONWORKLST) && bo->bo_dirty.bv_cnt == 0) {
                bo->bo_flag &= ~BO_ONWORKLST;
                mtx_lock(&sync_mtx);
                LIST_REMOVE(bo, bo_synclist);
                syncer_worklist_len--;
                mtx_unlock(&sync_mtx);
        }
        bp->b_vp = NULL;
        bp->b_bufobj = NULL;
        BO_UNLOCK(bo);
        vdrop(vp);
}

/*
 * Add an item to the syncer work queue.
 */
static void
vn_syncer_add_to_worklist(struct bufobj *bo, int delay)
{
        int slot;

        ASSERT_BO_WLOCKED(bo);

        mtx_lock(&sync_mtx);
        if (bo->bo_flag & BO_ONWORKLST)
                LIST_REMOVE(bo, bo_synclist);
        else {
                bo->bo_flag |= BO_ONWORKLST;
                syncer_worklist_len++;
        }

        if (delay > syncer_maxdelay - 2)
                delay = syncer_maxdelay - 2;
        slot = (syncer_delayno + delay) & syncer_mask;

        LIST_INSERT_HEAD(&syncer_workitem_pending[slot], bo, bo_synclist);
        mtx_unlock(&sync_mtx);
}

static int
sysctl_vfs_worklist_len(SYSCTL_HANDLER_ARGS)
{
        int error, len;

        mtx_lock(&sync_mtx);
        len = syncer_worklist_len - sync_vnode_count;
        mtx_unlock(&sync_mtx);
        error = SYSCTL_OUT(req, &len, sizeof(len));
        return (error);
}

SYSCTL_PROC(_vfs, OID_AUTO, worklist_len,
    CTLTYPE_INT | CTLFLAG_MPSAFE| CTLFLAG_RD, NULL, 0,
    sysctl_vfs_worklist_len, "I", "Syncer thread worklist length");

static struct proc *updateproc;
static void sched_sync(void);
static struct kproc_desc up_kp = {
        "syncer",
        sched_sync,
        &updateproc
};
SYSINIT(syncer, SI_SUB_KTHREAD_UPDATE, SI_ORDER_FIRST, kproc_start, &up_kp);

static int
sync_vnode(struct synclist *slp, struct bufobj **bo, struct thread *td)
{
        struct vnode *vp;
        struct mount *mp;

        *bo = LIST_FIRST(slp);
        if (*bo == NULL)
                return (0);
        vp = bo2vnode(*bo);
        if (VOP_ISLOCKED(vp) != 0 || VI_TRYLOCK(vp) == 0)
                return (1);
        /*
         * We use vhold in case the vnode does not
         * successfully sync.  vhold prevents the vnode from
         * going away when we unlock the sync_mtx so that
         * we can acquire the vnode interlock.
         */
        vholdl(vp);
        mtx_unlock(&sync_mtx);
        VI_UNLOCK(vp);
        if (vn_start_write(vp, &mp, V_NOWAIT) != 0) {
                vdrop(vp);
                mtx_lock(&sync_mtx);
                return (*bo == LIST_FIRST(slp));
        }
        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
        (void) VOP_FSYNC(vp, MNT_LAZY, td);
        VOP_UNLOCK(vp);
        vn_finished_write(mp);
        BO_LOCK(*bo);
        if (((*bo)->bo_flag & BO_ONWORKLST) != 0) {
                /*
                 * Put us back on the worklist.  The worklist
                 * routine will remove us from our current
                 * position and then add us back in at a later
                 * position.
                 */
                vn_syncer_add_to_worklist(*bo, syncdelay);
        }
        BO_UNLOCK(*bo);
        vdrop(vp);
        mtx_lock(&sync_mtx);
        return (0);
}

static int first_printf = 1;

/*
 * System filesystem synchronizer daemon.
 */
static void
sched_sync(void)
{
        struct synclist *next, *slp;
        struct bufobj *bo;
        long starttime;
        struct thread *td = curthread;
        int last_work_seen;
        int net_worklist_len;
        int syncer_final_iter;
        int error;

        last_work_seen = 0;
        syncer_final_iter = 0;
        syncer_state = SYNCER_RUNNING;
        starttime = time_uptime;
        td->td_pflags |= TDP_NORUNNINGBUF;

        EVENTHANDLER_REGISTER(shutdown_pre_sync, syncer_shutdown, td->td_proc,
            SHUTDOWN_PRI_LAST);

        mtx_lock(&sync_mtx);
        for (;;) {
                if (syncer_state == SYNCER_FINAL_DELAY &&
                    syncer_final_iter == 0) {
                        mtx_unlock(&sync_mtx);
                        kproc_suspend_check(td->td_proc);
                        mtx_lock(&sync_mtx);
                }
                net_worklist_len = syncer_worklist_len - sync_vnode_count;
                if (syncer_state != SYNCER_RUNNING &&
                    starttime != time_uptime) {
                        if (first_printf) {
                                printf("\nSyncing disks, vnodes remaining... ");
                                first_printf = 0;
                        }
                        printf("%d ", net_worklist_len);
                }
                starttime = time_uptime;

                /*
                 * Push files whose dirty time has expired.  Be careful
                 * of interrupt race on slp queue.
                 *
                 * Skip over empty worklist slots when shutting down.
                 */
                do {
                        slp = &syncer_workitem_pending[syncer_delayno];
                        syncer_delayno += 1;
                        if (syncer_delayno == syncer_maxdelay)
                                syncer_delayno = 0;
                        next = &syncer_workitem_pending[syncer_delayno];
                        /*
                         * If the worklist has wrapped since the
                         * it was emptied of all but syncer vnodes,
                         * switch to the FINAL_DELAY state and run
                         * for one more second.
                         */
                        if (syncer_state == SYNCER_SHUTTING_DOWN &&
                            net_worklist_len == 0 &&
                            last_work_seen == syncer_delayno) {
                                syncer_state = SYNCER_FINAL_DELAY;
                                syncer_final_iter = SYNCER_SHUTDOWN_SPEEDUP;
                        }
                } while (syncer_state != SYNCER_RUNNING && LIST_EMPTY(slp) &&
                    syncer_worklist_len > 0);

                /*
                 * Keep track of the last time there was anything
                 * on the worklist other than syncer vnodes.
                 * Return to the SHUTTING_DOWN state if any
                 * new work appears.
                 */
                if (net_worklist_len > 0 || syncer_state == SYNCER_RUNNING)
                        last_work_seen = syncer_delayno;
                if (net_worklist_len > 0 && syncer_state == SYNCER_FINAL_DELAY)
                        syncer_state = SYNCER_SHUTTING_DOWN;
                while (!LIST_EMPTY(slp)) {
                        error = sync_vnode(slp, &bo, td);
                        if (error == 1) {
                                LIST_REMOVE(bo, bo_synclist);
                                LIST_INSERT_HEAD(next, bo, bo_synclist);
                                continue;
                        }

                        if (first_printf == 0) {
                                /*
                                 * Drop the sync mutex, because some watchdog
                                 * drivers need to sleep while patting
                                 */
                                mtx_unlock(&sync_mtx);
                                wdog_kern_pat(WD_LASTVAL);
                                mtx_lock(&sync_mtx);
                        }

                }
                if (syncer_state == SYNCER_FINAL_DELAY && syncer_final_iter > 0)
                        syncer_final_iter--;
                /*
                 * The variable rushjob allows the kernel to speed up the
                 * processing of the filesystem syncer process. A rushjob
                 * value of N tells the filesystem syncer to process the next
                 * N seconds worth of work on its queue ASAP. Currently rushjob
                 * is used by the soft update code to speed up the filesystem
                 * syncer process when the incore state is getting so far
                 * ahead of the disk that the kernel memory pool is being
                 * threatened with exhaustion.
                 */
                if (rushjob > 0) {
                        rushjob -= 1;
                        continue;
                }
                /*
                 * Just sleep for a short period of time between
                 * iterations when shutting down to allow some I/O
                 * to happen.
                 *
                 * If it has taken us less than a second to process the
                 * current work, then wait. Otherwise start right over
                 * again. We can still lose time if any single round
                 * takes more than two seconds, but it does not really
                 * matter as we are just trying to generally pace the
                 * filesystem activity.
                 */
                if (syncer_state != SYNCER_RUNNING ||
                    time_uptime == starttime) {
                        thread_lock(td);
                        sched_prio(td, PPAUSE);
                        thread_unlock(td);
                }
                if (syncer_state != SYNCER_RUNNING)
                        cv_timedwait(&sync_wakeup, &sync_mtx,
                            hz / SYNCER_SHUTDOWN_SPEEDUP);
                else if (time_uptime == starttime)
                        cv_timedwait(&sync_wakeup, &sync_mtx, hz);
        }
}

/*
 * Request the syncer daemon to speed up its work.
 * We never push it to speed up more than half of its
 * normal turn time, otherwise it could take over the cpu.
 */
int
speedup_syncer(void)
{
        int ret = 0;

        mtx_lock(&sync_mtx);
        if (rushjob < syncdelay / 2) {
                rushjob += 1;
                stat_rush_requests += 1;
                ret = 1;
        }
        mtx_unlock(&sync_mtx);
        cv_broadcast(&sync_wakeup);
        return (ret);
}

/*
 * Tell the syncer to speed up its work and run though its work
 * list several times, then tell it to shut down.
 */
static void
syncer_shutdown(void *arg, int howto)
{

        if (howto & RB_NOSYNC)
                return;
        mtx_lock(&sync_mtx);
        syncer_state = SYNCER_SHUTTING_DOWN;
        rushjob = 0;
        mtx_unlock(&sync_mtx);
        cv_broadcast(&sync_wakeup);
        kproc_shutdown(arg, howto);
}

void
syncer_suspend(void)
{

        syncer_shutdown(updateproc, 0);
}

void
syncer_resume(void)
{

        mtx_lock(&sync_mtx);
        first_printf = 1;
        syncer_state = SYNCER_RUNNING;
        mtx_unlock(&sync_mtx);
        cv_broadcast(&sync_wakeup);
        kproc_resume(updateproc);
}

/*
 * Reassign a buffer from one vnode to another.
 * Used to assign file specific control information
 * (indirect blocks) to the vnode to which they belong.
 */
void
reassignbuf(struct buf *bp)
{
        struct vnode *vp;
        struct bufobj *bo;
        int delay;
#ifdef INVARIANTS
        struct bufv *bv;
#endif

        vp = bp->b_vp;
        bo = bp->b_bufobj;
        ++reassignbufcalls;

        CTR3(KTR_BUF, "reassignbuf(%p) vp %p flags %X",
            bp, bp->b_vp, bp->b_flags);
        /*
         * B_PAGING flagged buffers cannot be reassigned because their vp
         * is not fully linked in.
         */
        if (bp->b_flags & B_PAGING)
                panic("cannot reassign paging buffer");

        /*
         * Delete from old vnode list, if on one.
         */
        BO_LOCK(bo);
        if (bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN))
                buf_vlist_remove(bp);
        else
                panic("reassignbuf: Buffer %p not on queue.", bp);
        /*
         * If dirty, put on list of dirty buffers; otherwise insert onto list
         * of clean buffers.
         */
        if (bp->b_flags & B_DELWRI) {
                if ((bo->bo_flag & BO_ONWORKLST) == 0) {
                        switch (vp->v_type) {
                        case VDIR:
                                delay = dirdelay;
                                break;
                        case VCHR:
                                delay = metadelay;
                                break;
                        default:
                                delay = filedelay;
                        }
                        vn_syncer_add_to_worklist(bo, delay);
                }
                buf_vlist_add(bp, bo, BX_VNDIRTY);
        } else {
                buf_vlist_add(bp, bo, BX_VNCLEAN);

                if ((bo->bo_flag & BO_ONWORKLST) && bo->bo_dirty.bv_cnt == 0) {
                        mtx_lock(&sync_mtx);
                        LIST_REMOVE(bo, bo_synclist);
                        syncer_worklist_len--;
                        mtx_unlock(&sync_mtx);
                        bo->bo_flag &= ~BO_ONWORKLST;
                }
        }
#ifdef INVARIANTS
        bv = &bo->bo_clean;
        bp = TAILQ_FIRST(&bv->bv_hd);
        KASSERT(bp == NULL || bp->b_bufobj == bo,
            ("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
        bp = TAILQ_LAST(&bv->bv_hd, buflists);
        KASSERT(bp == NULL || bp->b_bufobj == bo,
            ("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
        bv = &bo->bo_dirty;
        bp = TAILQ_FIRST(&bv->bv_hd);
        KASSERT(bp == NULL || bp->b_bufobj == bo,
            ("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
        bp = TAILQ_LAST(&bv->bv_hd, buflists);
        KASSERT(bp == NULL || bp->b_bufobj == bo,
            ("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
#endif
        BO_UNLOCK(bo);
}

static void
v_init_counters(struct vnode *vp)
{

        VNASSERT(vp->v_type == VNON && vp->v_data == NULL && vp->v_iflag == 0,
            vp, ("%s called for an initialized vnode", __FUNCTION__));
        ASSERT_VI_UNLOCKED(vp, __FUNCTION__);

        refcount_init(&vp->v_holdcnt, 1);
        refcount_init(&vp->v_usecount, 1);
}

/*
 * Increment si_usecount of the associated device, if any.
 */
static void
v_incr_devcount(struct vnode *vp)
{

        ASSERT_VI_LOCKED(vp, __FUNCTION__);
        if (vp->v_type == VCHR && vp->v_rdev != NULL) {
                dev_lock();
                vp->v_rdev->si_usecount++;
                dev_unlock();
        }
}

/*
 * Decrement si_usecount of the associated device, if any.
 */
static void
v_decr_devcount(struct vnode *vp)
{

        ASSERT_VI_LOCKED(vp, __FUNCTION__);
        if (vp->v_type == VCHR && vp->v_rdev != NULL) {
                dev_lock();
                vp->v_rdev->si_usecount--;
                dev_unlock();
        }
}

/*
 * Grab a particular vnode from the free list, increment its
 * reference count and lock it.  VIRF_DOOMED is set if the vnode
 * is being destroyed.  Only callers who specify LK_RETRY will
 * see doomed vnodes.  If inactive processing was delayed in
 * vput try to do it here.
 *
 * usecount is manipulated using atomics without holding any locks.
 *
 * holdcnt can be manipulated using atomics without holding any locks,
 * except when transitioning 1<->0, in which case the interlock is held.
 */
enum vgetstate
vget_prep(struct vnode *vp)
{
        enum vgetstate vs;

        if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
                vs = VGET_USECOUNT;
        } else {
                vhold(vp);
                vs = VGET_HOLDCNT;
        }
        return (vs);
}

int
vget(struct vnode *vp, int flags, struct thread *td)
{
        enum vgetstate vs;

        MPASS(td == curthread);

        vs = vget_prep(vp);
        return (vget_finish(vp, flags, vs));
}

static int __noinline
vget_finish_vchr(struct vnode *vp)
{

        VNASSERT(vp->v_type == VCHR, vp, ("type != VCHR)"));

        /*
         * See the comment in vget_finish before usecount bump.
         */
        if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
#ifdef INVARIANTS
                int old = atomic_fetchadd_int(&vp->v_holdcnt, -1);
                VNASSERT(old > 0, vp, ("%s: wrong hold count %d", __func__, old));
#else
                refcount_release(&vp->v_holdcnt);
#endif
                return (0);
        }

        VI_LOCK(vp);
        if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
#ifdef INVARIANTS
                int old = atomic_fetchadd_int(&vp->v_holdcnt, -1);
                VNASSERT(old > 1, vp, ("%s: wrong hold count %d", __func__, old));
#else
                refcount_release(&vp->v_holdcnt);
#endif
                VI_UNLOCK(vp);
                return (0);
        }
        v_incr_devcount(vp);
        refcount_acquire(&vp->v_usecount);
        VI_UNLOCK(vp);
        return (0);
}

int
vget_finish(struct vnode *vp, int flags, enum vgetstate vs)
{
        int error, old;

        VNASSERT((flags & LK_TYPE_MASK) != 0, vp,
            ("%s: invalid lock operation", __func__));

        if ((flags & LK_INTERLOCK) != 0)
                ASSERT_VI_LOCKED(vp, __func__);
        else
                ASSERT_VI_UNLOCKED(vp, __func__);
        VNASSERT(vp->v_holdcnt > 0, vp, ("%s: vnode not held", __func__));
        if (vs == VGET_USECOUNT) {
                VNASSERT(vp->v_usecount > 0, vp,
                    ("%s: vnode without usecount when VGET_USECOUNT was passed",
                    __func__));
        }

        error = vn_lock(vp, flags);
        if (__predict_false(error != 0)) {
                if (vs == VGET_USECOUNT)
                        vrele(vp);
                else
                        vdrop(vp);
                CTR2(KTR_VFS, "%s: impossible to lock vnode %p", __func__,
                    vp);
                return (error);
        }

        if (vs == VGET_USECOUNT) {
                return (0);
        }

        if (__predict_false(vp->v_type == VCHR))
                return (vget_finish_vchr(vp));

        /*
         * We hold the vnode. If the usecount is 0 it will be utilized to keep
         * the vnode around. Otherwise someone else lended their hold count and
         * we have to drop ours.
         */
        old = atomic_fetchadd_int(&vp->v_usecount, 1);
        VNASSERT(old >= 0, vp, ("%s: wrong use count %d", __func__, old));
        if (old != 0) {
#ifdef INVARIANTS
                old = atomic_fetchadd_int(&vp->v_holdcnt, -1);
                VNASSERT(old > 1, vp, ("%s: wrong hold count %d", __func__, old));
#else
                refcount_release(&vp->v_holdcnt);
#endif
        }
        return (0);
}

/*
 * Increase the reference (use) and hold count of a vnode.
 * This will also remove the vnode from the free list if it is presently free.
 */
static void __noinline
vref_vchr(struct vnode *vp, bool interlock)
{

        /*
         * See the comment in vget_finish before usecount bump.
         */
        if (!interlock) {
                if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
                        VNODE_REFCOUNT_FENCE_ACQ();
                        VNASSERT(vp->v_holdcnt > 0, vp,
                            ("%s: active vnode not held", __func__));
                        return;
                }
                VI_LOCK(vp);
                /*
                 * By the time we get here the vnode might have been doomed, at
                 * which point the 0->1 use count transition is no longer
                 * protected by the interlock. Since it can't bounce back to
                 * VCHR and requires vref semantics, punt it back
                 */
                if (__predict_false(vp->v_type == VBAD)) {
                        VI_UNLOCK(vp);
                        vref(vp);
                        return;
                }
        }
        VNASSERT(vp->v_type == VCHR, vp, ("type != VCHR)"));
        if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
                VNODE_REFCOUNT_FENCE_ACQ();
                VNASSERT(vp->v_holdcnt > 0, vp,
                    ("%s: active vnode not held", __func__));
                if (!interlock)
                        VI_UNLOCK(vp);
                return;
        }
        vhold(vp);
        v_incr_devcount(vp);
        refcount_acquire(&vp->v_usecount);
        if (!interlock)
                VI_UNLOCK(vp);
        return;
}

void
vref(struct vnode *vp)
{
        int old;

        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        if (__predict_false(vp->v_type == VCHR)) {
                 vref_vchr(vp, false);
                 return;
        }

        if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
                VNODE_REFCOUNT_FENCE_ACQ();
                VNASSERT(vp->v_holdcnt > 0, vp,
                    ("%s: active vnode not held", __func__));
                return;
        }
        vhold(vp);
        /*
         * See the comment in vget_finish.
         */
        old = atomic_fetchadd_int(&vp->v_usecount, 1);
        VNASSERT(old >= 0, vp, ("%s: wrong use count %d", __func__, old));
        if (old != 0) {
#ifdef INVARIANTS
                old = atomic_fetchadd_int(&vp->v_holdcnt, -1);
                VNASSERT(old > 1, vp, ("%s: wrong hold count %d", __func__, old));
#else
                refcount_release(&vp->v_holdcnt);
#endif
        }
}

void
vrefl(struct vnode *vp)
{

        ASSERT_VI_LOCKED(vp, __func__);
        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        if (__predict_false(vp->v_type == VCHR)) {
                vref_vchr(vp, true);
                return;
        }
        vref(vp);
}

void
vrefact(struct vnode *vp)
{

        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
#ifdef INVARIANTS
        int old = atomic_fetchadd_int(&vp->v_usecount, 1);
        VNASSERT(old > 0, vp, ("%s: wrong use count %d", __func__, old));
#else
        refcount_acquire(&vp->v_usecount);
#endif
}

/*
 * Return reference count of a vnode.
 *
 * The results of this call are only guaranteed when some mechanism is used to
 * stop other processes from gaining references to the vnode.  This may be the
 * case if the caller holds the only reference.  This is also useful when stale
 * data is acceptable as race conditions may be accounted for by some other
 * means.
 */
int
vrefcnt(struct vnode *vp)
{

        return (vp->v_usecount);
}

void
vlazy(struct vnode *vp)
{
        struct mount *mp;

        VNASSERT(vp->v_holdcnt > 0, vp, ("%s: vnode not held", __func__));

        if ((vp->v_mflag & VMP_LAZYLIST) != 0)
                return;
        mp = vp->v_mount;
        mtx_lock(&mp->mnt_listmtx);
        if ((vp->v_mflag & VMP_LAZYLIST) == 0) {
                vp->v_mflag |= VMP_LAZYLIST;
                TAILQ_INSERT_TAIL(&mp->mnt_lazyvnodelist, vp, v_lazylist);
                mp->mnt_lazyvnodelistsize++;
        }
        mtx_unlock(&mp->mnt_listmtx);
}

static void
vdefer_inactive(struct vnode *vp)
{

        ASSERT_VI_LOCKED(vp, __func__);
        VNASSERT(vp->v_holdcnt > 0, vp,
            ("%s: vnode without hold count", __func__));
        if (VN_IS_DOOMED(vp)) {
                vdropl(vp);
                return;
        }
        if (vp->v_iflag & VI_DEFINACT) {
                VNASSERT(vp->v_holdcnt > 1, vp, ("lost hold count"));
                vdropl(vp);
                return;
        }
        if (vp->v_usecount > 0) {
                vp->v_iflag &= ~VI_OWEINACT;
                vdropl(vp);
                return;
        }
        vlazy(vp);
        vp->v_iflag |= VI_DEFINACT;
        VI_UNLOCK(vp);
        counter_u64_add(deferred_inact, 1);
}

static void
vdefer_inactive_unlocked(struct vnode *vp)
{

        VI_LOCK(vp);
        if ((vp->v_iflag & VI_OWEINACT) == 0) {
                vdropl(vp);
                return;
        }
        vdefer_inactive(vp);
}

enum vputx_op { VPUTX_VRELE, VPUTX_VPUT, VPUTX_VUNREF };

/*
 * Decrement the use and hold counts for a vnode.
 *
 * See an explanation near vget() as to why atomic operation is safe.
 *
 * XXX Some filesystems pass in an exclusively locked vnode and strongly depend
 * on the lock being held all the way until VOP_INACTIVE. This in particular
 * happens with UFS which adds half-constructed vnodes to the hash, where they
 * can be found by other code.
 */
static void
vputx(struct vnode *vp, enum vputx_op func)
{
        int error;

        KASSERT(vp != NULL, ("vputx: null vp"));
        if (func == VPUTX_VUNREF)
                ASSERT_VOP_LOCKED(vp, "vunref");
        else if (func == VPUTX_VPUT)
                ASSERT_VOP_LOCKED(vp, "vput");
        ASSERT_VI_UNLOCKED(vp, __func__);
        VNASSERT(vp->v_holdcnt > 0 && vp->v_usecount > 0, vp,
            ("%s: wrong ref counts", __func__));

        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);

        /*
         * We want to hold the vnode until the inactive finishes to
         * prevent vgone() races.  We drop the use count here and the
         * hold count below when we're done.
         *
         * If we release the last usecount we take ownership of the hold
         * count which provides liveness of the vnode, in which case we
         * have to vdrop.
         */
        if (!refcount_release(&vp->v_usecount)) {
                if (func == VPUTX_VPUT)
                        VOP_UNLOCK(vp);
                return;
        }
        VI_LOCK(vp);
        v_decr_devcount(vp);
        /*
         * By the time we got here someone else might have transitioned
         * the count back to > 0.
         */
        if (vp->v_usecount > 0 || vp->v_iflag & VI_DOINGINACT)
                goto out;

        /*
         * Check if the fs wants to perform inactive processing. Note we
         * may be only holding the interlock, in which case it is possible
         * someone else called vgone on the vnode and ->v_data is now NULL.
         * Since vgone performs inactive on its own there is nothing to do
         * here but to drop our hold count.
         */
        if (__predict_false(VN_IS_DOOMED(vp)) ||
            VOP_NEED_INACTIVE(vp) == 0)
                goto out;

        /*
         * We must call VOP_INACTIVE with the node locked. Mark
         * as VI_DOINGINACT to avoid recursion.
         */
        vp->v_iflag |= VI_OWEINACT;
        switch (func) {
        case VPUTX_VRELE:
                error = vn_lock(vp, LK_EXCLUSIVE | LK_INTERLOCK);
                VI_LOCK(vp);
                break;
        case VPUTX_VPUT:
                error = 0;
                if (VOP_ISLOCKED(vp) != LK_EXCLUSIVE) {
                        error = VOP_LOCK(vp, LK_UPGRADE | LK_INTERLOCK |
                            LK_NOWAIT);
                        VI_LOCK(vp);
                }
                break;
        case VPUTX_VUNREF:
                error = 0;
                if (VOP_ISLOCKED(vp) != LK_EXCLUSIVE) {
                        error = VOP_LOCK(vp, LK_TRYUPGRADE | LK_INTERLOCK);
                        VI_LOCK(vp);
                }
                break;
        }
        if (error == 0) {
                vinactive(vp);
                if (func != VPUTX_VUNREF)
                        VOP_UNLOCK(vp);
                vdropl(vp);
        } else {
                vdefer_inactive(vp);
        }
        return;
out:
        if (func == VPUTX_VPUT)
                VOP_UNLOCK(vp);
        vdropl(vp);
}

/*
 * Vnode put/release.
 * If count drops to zero, call inactive routine and return to freelist.
 */
void
vrele(struct vnode *vp)
{

        vputx(vp, VPUTX_VRELE);
}

/*
 * Release an already locked vnode.  This give the same effects as
 * unlock+vrele(), but takes less time and avoids releasing and
 * re-aquiring the lock (as vrele() acquires the lock internally.)
 */
void
vput(struct vnode *vp)
{

        vputx(vp, VPUTX_VPUT);
}

/*
 * Release an exclusively locked vnode. Do not unlock the vnode lock.
 */
void
vunref(struct vnode *vp)
{

        vputx(vp, VPUTX_VUNREF);
}

void
vhold(struct vnode *vp)
{
        struct vdbatch *vd;
        int old;

        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        old = atomic_fetchadd_int(&vp->v_holdcnt, 1);
        VNASSERT(old >= 0, vp, ("%s: wrong hold count %d", __func__, old));
        if (old != 0)
                return;
        critical_enter();
        vd = DPCPU_PTR(vd);
        vd->freevnodes--;
        critical_exit();
}

void
vholdl(struct vnode *vp)
{

        ASSERT_VI_LOCKED(vp, __func__);
        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        vhold(vp);
}

void
vholdnz(struct vnode *vp)
{

        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
#ifdef INVARIANTS
        int old = atomic_fetchadd_int(&vp->v_holdcnt, 1);
        VNASSERT(old > 0, vp, ("%s: wrong hold count %d", __func__, old));
#else
        atomic_add_int(&vp->v_holdcnt, 1);
#endif
}

static void __noinline
vdbatch_process(struct vdbatch *vd)
{
        struct vnode *vp;
        int i;

        mtx_assert(&vd->lock, MA_OWNED);
        MPASS(curthread->td_pinned > 0);
        MPASS(vd->index == VDBATCH_SIZE);

        mtx_lock(&vnode_list_mtx);
        critical_enter();
        freevnodes += vd->freevnodes;
        for (i = 0; i < VDBATCH_SIZE; i++) {
                vp = vd->tab[i];
                TAILQ_REMOVE(&vnode_list, vp, v_vnodelist);
                TAILQ_INSERT_TAIL(&vnode_list, vp, v_vnodelist);
                MPASS(vp->v_dbatchcpu != NOCPU);
                vp->v_dbatchcpu = NOCPU;
        }
        mtx_unlock(&vnode_list_mtx);
        vd->freevnodes = 0;
        bzero(vd->tab, sizeof(vd->tab));
        vd->index = 0;
        critical_exit();
}

static void
vdbatch_enqueue(struct vnode *vp)
{
        struct vdbatch *vd;

        ASSERT_VI_LOCKED(vp, __func__);
        VNASSERT(!VN_IS_DOOMED(vp), vp,
            ("%s: deferring requeue of a doomed vnode", __func__));

        critical_enter();
        vd = DPCPU_PTR(vd);
        vd->freevnodes++;
        if (vp->v_dbatchcpu != NOCPU) {
                VI_UNLOCK(vp);
                critical_exit();
                return;
        }

        sched_pin();
        critical_exit();
        mtx_lock(&vd->lock);
        MPASS(vd->index < VDBATCH_SIZE);
        MPASS(vd->tab[vd->index] == NULL);
        /*
         * A hack: we depend on being pinned so that we know what to put in
         * ->v_dbatchcpu.
         */
        vp->v_dbatchcpu = curcpu;
        vd->tab[vd->index] = vp;
        vd->index++;
        VI_UNLOCK(vp);
        if (vd->index == VDBATCH_SIZE)
                vdbatch_process(vd);
        mtx_unlock(&vd->lock);
        sched_unpin();
}

/*
 * This routine must only be called for vnodes which are about to be
 * deallocated. Supporting dequeue for arbitrary vndoes would require
 * validating that the locked batch matches.
 */
static void
vdbatch_dequeue(struct vnode *vp)
{
        struct vdbatch *vd;
        int i;
        short cpu;

        VNASSERT(vp->v_type == VBAD || vp->v_type == VNON, vp,
            ("%s: called for a used vnode\n", __func__));

        cpu = vp->v_dbatchcpu;
        if (cpu == NOCPU)
                return;

        vd = DPCPU_ID_PTR(cpu, vd);
        mtx_lock(&vd->lock);
        for (i = 0; i < vd->index; i++) {
                if (vd->tab[i] != vp)
                        continue;
                vp->v_dbatchcpu = NOCPU;
                vd->index--;
                vd->tab[i] = vd->tab[vd->index];
                vd->tab[vd->index] = NULL;
                break;
        }
        mtx_unlock(&vd->lock);
        /*
         * Either we dequeued the vnode above or the target CPU beat us to it.
         */
        MPASS(vp->v_dbatchcpu == NOCPU);
}

/*
 * Drop the hold count of the vnode.  If this is the last reference to
 * the vnode we place it on the free list unless it has been vgone'd
 * (marked VIRF_DOOMED) in which case we will free it.
 *
 * Because the vnode vm object keeps a hold reference on the vnode if
 * there is at least one resident non-cached page, the vnode cannot
 * leave the active list without the page cleanup done.
 */
static void
vdrop_deactivate(struct vnode *vp)
{
        struct mount *mp;

        ASSERT_VI_LOCKED(vp, __func__);
        /*
         * Mark a vnode as free: remove it from its active list
         * and put it up for recycling on the freelist.
         */
        VNASSERT(!VN_IS_DOOMED(vp), vp,
            ("vdrop: returning doomed vnode"));
        VNASSERT(vp->v_op != NULL, vp,
            ("vdrop: vnode already reclaimed."));
        VNASSERT((vp->v_iflag & VI_OWEINACT) == 0, vp,
            ("vnode with VI_OWEINACT set"));
        VNASSERT((vp->v_iflag & VI_DEFINACT) == 0, vp,
            ("vnode with VI_DEFINACT set"));
        if (vp->v_mflag & VMP_LAZYLIST) {
                mp = vp->v_mount;
                mtx_lock(&mp->mnt_listmtx);
                VNASSERT(vp->v_mflag & VMP_LAZYLIST, vp, ("lost VMP_LAZYLIST"));
                /*
                 * Don't remove the vnode from the lazy list if another thread
                 * has increased the hold count. It may have re-enqueued the
                 * vnode to the lazy list and is now responsible for its
                 * removal.
                 */
                if (vp->v_holdcnt == 0) {
                        vp->v_mflag &= ~VMP_LAZYLIST;
                        TAILQ_REMOVE(&mp->mnt_lazyvnodelist, vp, v_lazylist);
                        mp->mnt_lazyvnodelistsize--;
                }
                mtx_unlock(&mp->mnt_listmtx);
        }
        vdbatch_enqueue(vp);
}

void
vdrop(struct vnode *vp)
{

        ASSERT_VI_UNLOCKED(vp, __func__);
        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        if (refcount_release_if_not_last(&vp->v_holdcnt))
                return;
        VI_LOCK(vp);
        vdropl(vp);
}

void
vdropl(struct vnode *vp)
{

        ASSERT_VI_LOCKED(vp, __func__);
        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        if (!refcount_release(&vp->v_holdcnt)) {
                VI_UNLOCK(vp);
                return;
        }
        if (VN_IS_DOOMED(vp)) {
                freevnode(vp);
                return;
        }
        vdrop_deactivate(vp);
}

/*
 * Call VOP_INACTIVE on the vnode and manage the DOINGINACT and OWEINACT
 * flags.  DOINGINACT prevents us from recursing in calls to vinactive.
 */
static void
vinactivef(struct vnode *vp)
{
        struct vm_object *obj;

        ASSERT_VOP_ELOCKED(vp, "vinactive");
        ASSERT_VI_LOCKED(vp, "vinactive");
        VNASSERT((vp->v_iflag & VI_DOINGINACT) == 0, vp,
            ("vinactive: recursed on VI_DOINGINACT"));
        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        vp->v_iflag |= VI_DOINGINACT;
        vp->v_iflag &= ~VI_OWEINACT;
        VI_UNLOCK(vp);
        /*
         * Before moving off the active list, we must be sure that any
         * modified pages are converted into the vnode's dirty
         * buffers, since these will no longer be checked once the
         * vnode is on the inactive list.
         *
         * The write-out of the dirty pages is asynchronous.  At the
         * point that VOP_INACTIVE() is called, there could still be
         * pending I/O and dirty pages in the object.
         */
        if ((obj = vp->v_object) != NULL && (vp->v_vflag & VV_NOSYNC) == 0 &&
            vm_object_mightbedirty(obj)) {
                VM_OBJECT_WLOCK(obj);
                vm_object_page_clean(obj, 0, 0, 0);
                VM_OBJECT_WUNLOCK(obj);
        }
        VOP_INACTIVE(vp, curthread);
        VI_LOCK(vp);
        VNASSERT(vp->v_iflag & VI_DOINGINACT, vp,
            ("vinactive: lost VI_DOINGINACT"));
        vp->v_iflag &= ~VI_DOINGINACT;
}

void
vinactive(struct vnode *vp)
{

        ASSERT_VOP_ELOCKED(vp, "vinactive");
        ASSERT_VI_LOCKED(vp, "vinactive");
        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);

        if ((vp->v_iflag & VI_OWEINACT) == 0)
                return;
        if (vp->v_iflag & VI_DOINGINACT)
                return;
        if (vp->v_usecount > 0) {
                vp->v_iflag &= ~VI_OWEINACT;
                return;
        }
        vinactivef(vp);
}

/*
 * Remove any vnodes in the vnode table belonging to mount point mp.
 *
 * If FORCECLOSE is not specified, there should not be any active ones,
 * return error if any are found (nb: this is a user error, not a
 * system error). If FORCECLOSE is specified, detach any active vnodes
 * that are found.
 *
 * If WRITECLOSE is set, only flush out regular file vnodes open for
 * writing.
 *
 * SKIPSYSTEM causes any vnodes marked VV_SYSTEM to be skipped.
 *
 * `rootrefs' specifies the base reference count for the root vnode
 * of this filesystem. The root vnode is considered busy if its
 * v_usecount exceeds this value. On a successful return, vflush(, td)
 * will call vrele() on the root vnode exactly rootrefs times.
 * If the SKIPSYSTEM or WRITECLOSE flags are specified, rootrefs must
 * be zero.
 */
#ifdef DIAGNOSTIC
static int busyprt = 0;         /* print out busy vnodes */
SYSCTL_INT(_debug, OID_AUTO, busyprt, CTLFLAG_RW, &busyprt, 0, "Print out busy vnodes");
#endif

int
vflush(struct mount *mp, int rootrefs, int flags, struct thread *td)
{
        struct vnode *vp, *mvp, *rootvp = NULL;
        struct vattr vattr;
        int busy = 0, error;

        CTR4(KTR_VFS, "%s: mp %p with rootrefs %d and flags %d", __func__, mp,
            rootrefs, flags);
        if (rootrefs > 0) {
                KASSERT((flags & (SKIPSYSTEM | WRITECLOSE)) == 0,
                    ("vflush: bad args"));
                /*
                 * Get the filesystem root vnode. We can vput() it
                 * immediately, since with rootrefs > 0, it won't go away.
                 */
                if ((error = VFS_ROOT(mp, LK_EXCLUSIVE, &rootvp)) != 0) {
                        CTR2(KTR_VFS, "%s: vfs_root lookup failed with %d",
                            __func__, error);
                        return (error);
                }
                vput(rootvp);
        }
loop:
        MNT_VNODE_FOREACH_ALL(vp, mp, mvp) {
                vholdl(vp);
                error = vn_lock(vp, LK_INTERLOCK | LK_EXCLUSIVE);
                if (error) {
                        vdrop(vp);
                        MNT_VNODE_FOREACH_ALL_ABORT(mp, mvp);
                        goto loop;
                }
                /*
                 * Skip over a vnodes marked VV_SYSTEM.
                 */
                if ((flags & SKIPSYSTEM) && (vp->v_vflag & VV_SYSTEM)) {
                        VOP_UNLOCK(vp);
                        vdrop(vp);
                        continue;
                }
                /*
                 * If WRITECLOSE is set, flush out unlinked but still open
                 * files (even if open only for reading) and regular file
                 * vnodes open for writing.
                 */
                if (flags & WRITECLOSE) {
                        if (vp->v_object != NULL) {
                                VM_OBJECT_WLOCK(vp->v_object);
                                vm_object_page_clean(vp->v_object, 0, 0, 0);
                                VM_OBJECT_WUNLOCK(vp->v_object);
                        }
                        error = VOP_FSYNC(vp, MNT_WAIT, td);
                        if (error != 0) {
                                VOP_UNLOCK(vp);
                                vdrop(vp);
                                MNT_VNODE_FOREACH_ALL_ABORT(mp, mvp);
                                return (error);
                        }
                        error = VOP_GETATTR(vp, &vattr, td->td_ucred);
                        VI_LOCK(vp);

                        if ((vp->v_type == VNON ||
                            (error == 0 && vattr.va_nlink > 0)) &&
                            (vp->v_writecount <= 0 || vp->v_type != VREG)) {
                                VOP_UNLOCK(vp);
                                vdropl(vp);
                                continue;
                        }
                } else
                        VI_LOCK(vp);
                /*
                 * With v_usecount == 0, all we need to do is clear out the
                 * vnode data structures and we are done.
                 *
                 * If FORCECLOSE is set, forcibly close the vnode.
                 */
                if (vp->v_usecount == 0 || (flags & FORCECLOSE)) {
                        vgonel(vp);
                } else {
                        busy++;
#ifdef DIAGNOSTIC
                        if (busyprt)
                                vn_printf(vp, "vflush: busy vnode ");
#endif
                }
                VOP_UNLOCK(vp);
                vdropl(vp);
        }
        if (rootrefs > 0 && (flags & FORCECLOSE) == 0) {
                /*
                 * If just the root vnode is busy, and if its refcount
                 * is equal to `rootrefs', then go ahead and kill it.
                 */
                VI_LOCK(rootvp);
                KASSERT(busy > 0, ("vflush: not busy"));
                VNASSERT(rootvp->v_usecount >= rootrefs, rootvp,
                    ("vflush: usecount %d < rootrefs %d",
                     rootvp->v_usecount, rootrefs));
                if (busy == 1 && rootvp->v_usecount == rootrefs) {
                        VOP_LOCK(rootvp, LK_EXCLUSIVE|LK_INTERLOCK);
                        vgone(rootvp);
                        VOP_UNLOCK(rootvp);
                        busy = 0;
                } else
                        VI_UNLOCK(rootvp);
        }
        if (busy) {
                CTR2(KTR_VFS, "%s: failing as %d vnodes are busy", __func__,
                    busy);
                return (EBUSY);
        }
        for (; rootrefs > 0; rootrefs--)
                vrele(rootvp);
        return (0);
}

/*
 * Recycle an unused vnode to the front of the free list.
 */
int
vrecycle(struct vnode *vp)
{
        int recycled;

        VI_LOCK(vp);
        recycled = vrecyclel(vp);
        VI_UNLOCK(vp);
        return (recycled);
}

/*
 * vrecycle, with the vp interlock held.
 */
int
vrecyclel(struct vnode *vp)
{
        int recycled;

        ASSERT_VOP_ELOCKED(vp, __func__);
        ASSERT_VI_LOCKED(vp, __func__);
        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        recycled = 0;
        if (vp->v_usecount == 0) {
                recycled = 1;
                vgonel(vp);
        }
        return (recycled);
}

/*
 * Eliminate all activity associated with a vnode
 * in preparation for reuse.
 */
void
vgone(struct vnode *vp)
{
        VI_LOCK(vp);
        vgonel(vp);
        VI_UNLOCK(vp);
}

static void
notify_lowervp_vfs_dummy(struct mount *mp __unused,
    struct vnode *lowervp __unused)
{
}

/*
 * Notify upper mounts about reclaimed or unlinked vnode.
 */
void
vfs_notify_upper(struct vnode *vp, int event)
{
        static struct vfsops vgonel_vfsops = {
                .vfs_reclaim_lowervp = notify_lowervp_vfs_dummy,
                .vfs_unlink_lowervp = notify_lowervp_vfs_dummy,
        };
        struct mount *mp, *ump, *mmp;

        mp = vp->v_mount;
        if (mp == NULL)
                return;
        if (TAILQ_EMPTY(&mp->mnt_uppers))
                return;

        mmp = malloc(sizeof(struct mount), M_TEMP, M_WAITOK | M_ZERO);
        mmp->mnt_op = &vgonel_vfsops;
        mmp->mnt_kern_flag |= MNTK_MARKER;
        MNT_ILOCK(mp);
        mp->mnt_kern_flag |= MNTK_VGONE_UPPER;
        for (ump = TAILQ_FIRST(&mp->mnt_uppers); ump != NULL;) {
                if ((ump->mnt_kern_flag & MNTK_MARKER) != 0) {
                        ump = TAILQ_NEXT(ump, mnt_upper_link);
                        continue;
                }
                TAILQ_INSERT_AFTER(&mp->mnt_uppers, ump, mmp, mnt_upper_link);
                MNT_IUNLOCK(mp);
                switch (event) {
                case VFS_NOTIFY_UPPER_RECLAIM:
                        VFS_RECLAIM_LOWERVP(ump, vp);
                        break;
                case VFS_NOTIFY_UPPER_UNLINK:
                        VFS_UNLINK_LOWERVP(ump, vp);
                        break;
                default:
                        KASSERT(0, ("invalid event %d", event));
                        break;
                }
                MNT_ILOCK(mp);
                ump = TAILQ_NEXT(mmp, mnt_upper_link);
                TAILQ_REMOVE(&mp->mnt_uppers, mmp, mnt_upper_link);
        }
        free(mmp, M_TEMP);
        mp->mnt_kern_flag &= ~MNTK_VGONE_UPPER;
        if ((mp->mnt_kern_flag & MNTK_VGONE_WAITER) != 0) {
                mp->mnt_kern_flag &= ~MNTK_VGONE_WAITER;
                wakeup(&mp->mnt_uppers);
        }
        MNT_IUNLOCK(mp);
}

/*
 * vgone, with the vp interlock held.
 */
static void
vgonel(struct vnode *vp)
{
        struct thread *td;
        struct mount *mp;
        vm_object_t object;
        bool active, oweinact;

        ASSERT_VOP_ELOCKED(vp, "vgonel");
        ASSERT_VI_LOCKED(vp, "vgonel");
        VNASSERT(vp->v_holdcnt, vp,
            ("vgonel: vp %p has no reference.", vp));
        CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
        td = curthread;

        /*
         * Don't vgonel if we're already doomed.
         */
        if (vp->v_irflag & VIRF_DOOMED)
                return;
        vp->v_irflag |= VIRF_DOOMED;

        /*
         * Check to see if the vnode is in use.  If so, we have to call
         * VOP_CLOSE() and VOP_INACTIVE().
         */
        active = vp->v_usecount > 0;
        oweinact = (vp->v_iflag & VI_OWEINACT) != 0;
        /*
         * If we need to do inactive VI_OWEINACT will be set.
         */
        if (vp->v_iflag & VI_DEFINACT) {
                VNASSERT(vp->v_holdcnt > 1, vp, ("lost hold count"));
                vp->v_iflag &= ~VI_DEFINACT;
                vdropl(vp);
        } else {
                VNASSERT(vp->v_holdcnt > 0, vp, ("vnode without hold count"));
                VI_UNLOCK(vp);
        }
        vfs_notify_upper(vp, VFS_NOTIFY_UPPER_RECLAIM);

        /*
         * If purging an active vnode, it must be closed and
         * deactivated before being reclaimed.
         */
        if (active)
                VOP_CLOSE(vp, FNONBLOCK, NOCRED, td);
        if (oweinact || active) {
                VI_LOCK(vp);
                vinactivef(vp);
                VI_UNLOCK(vp);
        }
        if (vp->v_type == VSOCK)
                vfs_unp_reclaim(vp);

        /*
         * Clean out any buffers associated with the vnode.
         * If the flush fails, just toss the buffers.
         */
        mp = NULL;
        if (!TAILQ_EMPTY(&vp->v_bufobj.bo_dirty.bv_hd))
                (void) vn_start_secondary_write(vp, &mp, V_WAIT);
        if (vinvalbuf(vp, V_SAVE, 0, 0) != 0) {
                while (vinvalbuf(vp, 0, 0, 0) != 0)
                        ;
        }

        BO_LOCK(&vp->v_bufobj);
        KASSERT(TAILQ_EMPTY(&vp->v_bufobj.bo_dirty.bv_hd) &&
            vp->v_bufobj.bo_dirty.bv_cnt == 0 &&
            TAILQ_EMPTY(&vp->v_bufobj.bo_clean.bv_hd) &&
            vp->v_bufobj.bo_clean.bv_cnt == 0,
            ("vp %p bufobj not invalidated", vp));

        /*
         * For VMIO bufobj, BO_DEAD is set later, or in
         * vm_object_terminate() after the object's page queue is
         * flushed.
         */
        object = vp->v_bufobj.bo_object;
        if (object == NULL)
                vp->v_bufobj.bo_flag |= BO_DEAD;
        BO_UNLOCK(&vp->v_bufobj);

        /*
         * Handle the VM part.  Tmpfs handles v_object on its own (the
         * OBJT_VNODE check).  Nullfs or other bypassing filesystems
         * should not touch the object borrowed from the lower vnode
         * (the handle check).
         */
        if (object != NULL && object->type == OBJT_VNODE &&
            object->handle == vp)
                vnode_destroy_vobject(vp);

        /*
         * Reclaim the vnode.
         */
        if (VOP_RECLAIM(vp, td))
                panic("vgone: cannot reclaim");
        if (mp != NULL)
                vn_finished_secondary_write(mp);
        VNASSERT(vp->v_object == NULL, vp,
            ("vop_reclaim left v_object vp=%p", vp));
        /*
         * Clear the advisory locks and wake up waiting threads.
         */
        (void)VOP_ADVLOCKPURGE(vp);
        vp->v_lockf = NULL;
        /*
         * Delete from old mount point vnode list.
         */
        delmntque(vp);
        cache_purge(vp);
        /*
         * Done with purge, reset to the standard lock and invalidate
         * the vnode.
         */
        VI_LOCK(vp);
        vp->v_vnlock = &vp->v_lock;
        vp->v_op = &dead_vnodeops;
        vp->v_type = VBAD;
}

/*
 * Calculate the total number of references to a special device.
 */
int
vcount(struct vnode *vp)
{
        int count;

        dev_lock();
        count = vp->v_rdev->si_usecount;
        dev_unlock();
        return (count);
}

/*
 * Print out a description of a vnode.
 */
static char *typename[] =
{"VNON", "VREG", "VDIR", "VBLK", "VCHR", "VLNK", "VSOCK", "VFIFO", "VBAD",
 "VMARKER"};

void
vn_printf(struct vnode *vp, const char *fmt, ...)
{
        va_list ap;
        char buf[256], buf2[16];
        u_long flags;

        va_start(ap, fmt);
        vprintf(fmt, ap);
        va_end(ap);
        printf("%p: ", (void *)vp);
        printf("type %s\n", typename[vp->v_type]);
        printf("    usecount %d, writecount %d, refcount %d",
            vp->v_usecount, vp->v_writecount, vp->v_holdcnt);
        switch (vp->v_type) {
        case VDIR:
                printf(" mountedhere %p\n", vp->v_mountedhere);
                break;
        case VCHR:
                printf(" rdev %p\n", vp->v_rdev);
                break;
        case VSOCK:
                printf(" socket %p\n", vp->v_unpcb);
                break;
        case VFIFO:
                printf(" fifoinfo %p\n", vp->v_fifoinfo);
                break;
        default:
                printf("\n");
                break;
        }
        buf[0] = '\0';
        buf[1] = '\0';
        if (vp->v_irflag & VIRF_DOOMED)
                strlcat(buf, "|VIRF_DOOMED", sizeof(buf));
        flags = vp->v_irflag & ~(VIRF_DOOMED);
        if (flags != 0) {
                snprintf(buf2, sizeof(buf2), "|VIRF(0x%lx)", flags);
                strlcat(buf, buf2, sizeof(buf));
        }
        if (vp->v_vflag & VV_ROOT)
                strlcat(buf, "|VV_ROOT", sizeof(buf));
        if (vp->v_vflag & VV_ISTTY)
                strlcat(buf, "|VV_ISTTY", sizeof(buf));
        if (vp->v_vflag & VV_NOSYNC)
                strlcat(buf, "|VV_NOSYNC", sizeof(buf));
        if (vp->v_vflag & VV_ETERNALDEV)
                strlcat(buf, "|VV_ETERNALDEV", sizeof(buf));
        if (vp->v_vflag & VV_CACHEDLABEL)
                strlcat(buf, "|VV_CACHEDLABEL", sizeof(buf));
        if (vp->v_vflag & VV_VMSIZEVNLOCK)
                strlcat(buf, "|VV_VMSIZEVNLOCK", sizeof(buf));
        if (vp->v_vflag & VV_COPYONWRITE)
                strlcat(buf, "|VV_COPYONWRITE", sizeof(buf));
        if (vp->v_vflag & VV_SYSTEM)
                strlcat(buf, "|VV_SYSTEM", sizeof(buf));
        if (vp->v_vflag & VV_PROCDEP)
                strlcat(buf, "|VV_PROCDEP", sizeof(buf));
        if (vp->v_vflag & VV_NOKNOTE)
                strlcat(buf, "|VV_NOKNOTE", sizeof(buf));
        if (vp->v_vflag & VV_DELETED)
                strlcat(buf, "|VV_DELETED", sizeof(buf));
        if (vp->v_vflag & VV_MD)
                strlcat(buf, "|VV_MD", sizeof(buf));
        if (vp->v_vflag & VV_FORCEINSMQ)
                strlcat(buf, "|VV_FORCEINSMQ", sizeof(buf));
        if (vp->v_vflag & VV_READLINK)
                strlcat(buf, "|VV_READLINK", sizeof(buf));
        flags = vp->v_vflag & ~(VV_ROOT | VV_ISTTY | VV_NOSYNC | VV_ETERNALDEV |
            VV_CACHEDLABEL | VV_COPYONWRITE | VV_SYSTEM | VV_PROCDEP |
            VV_NOKNOTE | VV_DELETED | VV_MD | VV_FORCEINSMQ);
        if (flags != 0) {
                snprintf(buf2, sizeof(buf2), "|VV(0x%lx)", flags);
                strlcat(buf, buf2, sizeof(buf));
        }
        if (vp->v_iflag & VI_TEXT_REF)
                strlcat(buf, "|VI_TEXT_REF", sizeof(buf));
        if (vp->v_iflag & VI_MOUNT)
                strlcat(buf, "|VI_MOUNT", sizeof(buf));
        if (vp->v_iflag & VI_DOINGINACT)
                strlcat(buf, "|VI_DOINGINACT", sizeof(buf));
        if (vp->v_iflag & VI_OWEINACT)
                strlcat(buf, "|VI_OWEINACT", sizeof(buf));
        if (vp->v_iflag & VI_DEFINACT)
                strlcat(buf, "|VI_DEFINACT", sizeof(buf));
        flags = vp->v_iflag & ~(VI_TEXT_REF | VI_MOUNT | VI_DOINGINACT |
            VI_OWEINACT | VI_DEFINACT);
        if (flags != 0) {
                snprintf(buf2, sizeof(buf2), "|VI(0x%lx)", flags);
                strlcat(buf, buf2, sizeof(buf));
        }
        if (vp->v_mflag & VMP_LAZYLIST)
                strlcat(buf, "|VMP_LAZYLIST", sizeof(buf));
        flags = vp->v_mflag & ~(VMP_LAZYLIST);
        if (flags != 0) {
                snprintf(buf2, sizeof(buf2), "|VMP(0x%lx)", flags);
                strlcat(buf, buf2, sizeof(buf));
        }
        printf("    flags (%s)\n", buf + 1);
        if (mtx_owned(VI_MTX(vp)))
                printf(" VI_LOCKed");
        if (vp->v_object != NULL)
                printf("    v_object %p ref %d pages %d "
                    "cleanbuf %d dirtybuf %d\n",
                    vp->v_object, vp->v_object->ref_count,
                    vp->v_object->resident_page_count,
                    vp->v_bufobj.bo_clean.bv_cnt,
                    vp->v_bufobj.bo_dirty.bv_cnt);
        printf("    ");
        lockmgr_printinfo(vp->v_vnlock);
        if (vp->v_data != NULL)
                VOP_PRINT(vp);
}

#ifdef DDB
/*
 * List all of the locked vnodes in the system.
 * Called when debugging the kernel.
 */
DB_SHOW_COMMAND(lockedvnods, lockedvnodes)
{
        struct mount *mp;
        struct vnode *vp;

        /*
         * Note: because this is DDB, we can't obey the locking semantics
         * for these structures, which means we could catch an inconsistent
         * state and dereference a nasty pointer.  Not much to be done
         * about that.
         */
        db_printf("Locked vnodes\n");
        TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                        if (vp->v_type != VMARKER && VOP_ISLOCKED(vp))
                                vn_printf(vp, "vnode ");
                }
        }
}

/*
 * Show details about the given vnode.
 */
DB_SHOW_COMMAND(vnode, db_show_vnode)
{
        struct vnode *vp;

        if (!have_addr)
                return;
        vp = (struct vnode *)addr;
        vn_printf(vp, "vnode ");
}

/*
 * Show details about the given mount point.
 */
DB_SHOW_COMMAND(mount, db_show_mount)
{
        struct mount *mp;
        struct vfsopt *opt;
        struct statfs *sp;
        struct vnode *vp;
        char buf[512];
        uint64_t mflags;
        u_int flags;

        if (!have_addr) {
                /* No address given, print short info about all mount points. */
                TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                        db_printf("%p %s on %s (%s)\n", mp,
                            mp->mnt_stat.f_mntfromname,
                            mp->mnt_stat.f_mntonname,
                            mp->mnt_stat.f_fstypename);
                        if (db_pager_quit)
                                break;
                }
                db_printf("\nMore info: show mount <addr>\n");
                return;
        }

        mp = (struct mount *)addr;
        db_printf("%p %s on %s (%s)\n", mp, mp->mnt_stat.f_mntfromname,
            mp->mnt_stat.f_mntonname, mp->mnt_stat.f_fstypename);

        buf[0] = '\0';
        mflags = mp->mnt_flag;
#define MNT_FLAG(flag)  do {                                            \
        if (mflags & (flag)) {                                          \
                if (buf[0] != '\0')                                     \
                        strlcat(buf, ", ", sizeof(buf));                \
                strlcat(buf, (#flag) + 4, sizeof(buf));                 \
                mflags &= ~(flag);                                      \
        }                                                               \
} while (0)
        MNT_FLAG(MNT_RDONLY);
        MNT_FLAG(MNT_SYNCHRONOUS);
        MNT_FLAG(MNT_NOEXEC);
        MNT_FLAG(MNT_NOSUID);
        MNT_FLAG(MNT_NFS4ACLS);
        MNT_FLAG(MNT_UNION);
        MNT_FLAG(MNT_ASYNC);
        MNT_FLAG(MNT_SUIDDIR);
        MNT_FLAG(MNT_SOFTDEP);
        MNT_FLAG(MNT_NOSYMFOLLOW);
        MNT_FLAG(MNT_GJOURNAL);
        MNT_FLAG(MNT_MULTILABEL);
        MNT_FLAG(MNT_ACLS);
        MNT_FLAG(MNT_NOATIME);
        MNT_FLAG(MNT_NOCLUSTERR);
        MNT_FLAG(MNT_NOCLUSTERW);
        MNT_FLAG(MNT_SUJ);
        MNT_FLAG(MNT_EXRDONLY);
        MNT_FLAG(MNT_EXPORTED);
        MNT_FLAG(MNT_DEFEXPORTED);
        MNT_FLAG(MNT_EXPORTANON);
        MNT_FLAG(MNT_EXKERB);
        MNT_FLAG(MNT_EXPUBLIC);
        MNT_FLAG(MNT_LOCAL);
        MNT_FLAG(MNT_QUOTA);
        MNT_FLAG(MNT_ROOTFS);
        MNT_FLAG(MNT_USER);
        MNT_FLAG(MNT_IGNORE);
        MNT_FLAG(MNT_UPDATE);
        MNT_FLAG(MNT_DELEXPORT);
        MNT_FLAG(MNT_RELOAD);
        MNT_FLAG(MNT_FORCE);
        MNT_FLAG(MNT_SNAPSHOT);
        MNT_FLAG(MNT_BYFSID);
#undef MNT_FLAG
        if (mflags != 0) {
                if (buf[0] != '\0')
                        strlcat(buf, ", ", sizeof(buf));
                snprintf(buf + strlen(buf), sizeof(buf) - strlen(buf),
                    "0x%016jx", mflags);
        }
        db_printf("    mnt_flag = %s\n", buf);

        buf[0] = '\0';
        flags = mp->mnt_kern_flag;
#define MNT_KERN_FLAG(flag)     do {                                    \
        if (flags & (flag)) {                                           \
                if (buf[0] != '\0')                                     \
                        strlcat(buf, ", ", sizeof(buf));                \
                strlcat(buf, (#flag) + 5, sizeof(buf));                 \
                flags &= ~(flag);                                       \
        }                                                               \
} while (0)
        MNT_KERN_FLAG(MNTK_UNMOUNTF);
        MNT_KERN_FLAG(MNTK_ASYNC);
        MNT_KERN_FLAG(MNTK_SOFTDEP);
        MNT_KERN_FLAG(MNTK_DRAINING);
        MNT_KERN_FLAG(MNTK_REFEXPIRE);
        MNT_KERN_FLAG(MNTK_EXTENDED_SHARED);
        MNT_KERN_FLAG(MNTK_SHARED_WRITES);
        MNT_KERN_FLAG(MNTK_NO_IOPF);
        MNT_KERN_FLAG(MNTK_VGONE_UPPER);
        MNT_KERN_FLAG(MNTK_VGONE_WAITER);
        MNT_KERN_FLAG(MNTK_LOOKUP_EXCL_DOTDOT);
        MNT_KERN_FLAG(MNTK_MARKER);
        MNT_KERN_FLAG(MNTK_USES_BCACHE);
        MNT_KERN_FLAG(MNTK_NOASYNC);
        MNT_KERN_FLAG(MNTK_UNMOUNT);
        MNT_KERN_FLAG(MNTK_MWAIT);
        MNT_KERN_FLAG(MNTK_SUSPEND);
        MNT_KERN_FLAG(MNTK_SUSPEND2);
        MNT_KERN_FLAG(MNTK_SUSPENDED);
        MNT_KERN_FLAG(MNTK_LOOKUP_SHARED);
        MNT_KERN_FLAG(MNTK_NOKNOTE);
#undef MNT_KERN_FLAG
        if (flags != 0) {
                if (buf[0] != '\0')
                        strlcat(buf, ", ", sizeof(buf));
                snprintf(buf + strlen(buf), sizeof(buf) - strlen(buf),
                    "0x%08x", flags);
        }
        db_printf("    mnt_kern_flag = %s\n", buf);

        db_printf("    mnt_opt = ");
        opt = TAILQ_FIRST(mp->mnt_opt);
        if (opt != NULL) {
                db_printf("%s", opt->name);
                opt = TAILQ_NEXT(opt, link);
                while (opt != NULL) {
                        db_printf(", %s", opt->name);
                        opt = TAILQ_NEXT(opt, link);
                }
        }
        db_printf("\n");

        sp = &mp->mnt_stat;
        db_printf("    mnt_stat = { version=%u type=%u flags=0x%016jx "
            "bsize=%ju iosize=%ju blocks=%ju bfree=%ju bavail=%jd files=%ju "
            "ffree=%jd syncwrites=%ju asyncwrites=%ju syncreads=%ju "
            "asyncreads=%ju namemax=%u owner=%u fsid=[%d, %d] }\n",
            (u_int)sp->f_version, (u_int)sp->f_type, (uintmax_t)sp->f_flags,
            (uintmax_t)sp->f_bsize, (uintmax_t)sp->f_iosize,
            (uintmax_t)sp->f_blocks, (uintmax_t)sp->f_bfree,
            (intmax_t)sp->f_bavail, (uintmax_t)sp->f_files,
            (intmax_t)sp->f_ffree, (uintmax_t)sp->f_syncwrites,
            (uintmax_t)sp->f_asyncwrites, (uintmax_t)sp->f_syncreads,
            (uintmax_t)sp->f_asyncreads, (u_int)sp->f_namemax,
            (u_int)sp->f_owner, (int)sp->f_fsid.val[0], (int)sp->f_fsid.val[1]);

        db_printf("    mnt_cred = { uid=%u ruid=%u",
            (u_int)mp->mnt_cred->cr_uid, (u_int)mp->mnt_cred->cr_ruid);
        if (jailed(mp->mnt_cred))
                db_printf(", jail=%d", mp->mnt_cred->cr_prison->pr_id);
        db_printf(" }\n");
        db_printf("    mnt_ref = %d (with %d in the struct)\n",
            vfs_mount_fetch_counter(mp, MNT_COUNT_REF), mp->mnt_ref);
        db_printf("    mnt_gen = %d\n", mp->mnt_gen);
        db_printf("    mnt_nvnodelistsize = %d\n", mp->mnt_nvnodelistsize);
        db_printf("    mnt_lazyvnodelistsize = %d\n",
            mp->mnt_lazyvnodelistsize);
        db_printf("    mnt_writeopcount = %d (with %d in the struct)\n",
            vfs_mount_fetch_counter(mp, MNT_COUNT_WRITEOPCOUNT), mp->mnt_writeopcount);
        db_printf("    mnt_maxsymlinklen = %d\n", mp->mnt_maxsymlinklen);
        db_printf("    mnt_iosize_max = %d\n", mp->mnt_iosize_max);
        db_printf("    mnt_hashseed = %u\n", mp->mnt_hashseed);
        db_printf("    mnt_lockref = %d (with %d in the struct)\n",
            vfs_mount_fetch_counter(mp, MNT_COUNT_LOCKREF), mp->mnt_lockref);
        db_printf("    mnt_secondary_writes = %d\n", mp->mnt_secondary_writes);
        db_printf("    mnt_secondary_accwrites = %d\n",
            mp->mnt_secondary_accwrites);
        db_printf("    mnt_gjprovider = %s\n",
            mp->mnt_gjprovider != NULL ? mp->mnt_gjprovider : "NULL");
        db_printf("    mnt_vfs_ops = %d\n", mp->mnt_vfs_ops);

        db_printf("\n\nList of active vnodes\n");
        TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                if (vp->v_type != VMARKER && vp->v_holdcnt > 0) {
                        vn_printf(vp, "vnode ");
                        if (db_pager_quit)
                                break;
                }
        }
        db_printf("\n\nList of inactive vnodes\n");
        TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                if (vp->v_type != VMARKER && vp->v_holdcnt == 0) {
                        vn_printf(vp, "vnode ");
                        if (db_pager_quit)
                                break;
                }
        }
}
#endif  /* DDB */

/*
 * Fill in a struct xvfsconf based on a struct vfsconf.
 */
static int
vfsconf2x(struct sysctl_req *req, struct vfsconf *vfsp)
{
        struct xvfsconf xvfsp;

        bzero(&xvfsp, sizeof(xvfsp));
        strcpy(xvfsp.vfc_name, vfsp->vfc_name);
        xvfsp.vfc_typenum = vfsp->vfc_typenum;
        xvfsp.vfc_refcount = vfsp->vfc_refcount;
        xvfsp.vfc_flags = vfsp->vfc_flags;
        /*
         * These are unused in userland, we keep them
         * to not break binary compatibility.
         */
        xvfsp.vfc_vfsops = NULL;
        xvfsp.vfc_next = NULL;
        return (SYSCTL_OUT(req, &xvfsp, sizeof(xvfsp)));
}

#ifdef COMPAT_FREEBSD32
struct xvfsconf32 {
        uint32_t        vfc_vfsops;
        char            vfc_name[MFSNAMELEN];
        int32_t         vfc_typenum;
        int32_t         vfc_refcount;
        int32_t         vfc_flags;
        uint32_t        vfc_next;
};

static int
vfsconf2x32(struct sysctl_req *req, struct vfsconf *vfsp)
{
        struct xvfsconf32 xvfsp;

        bzero(&xvfsp, sizeof(xvfsp));
        strcpy(xvfsp.vfc_name, vfsp->vfc_name);
        xvfsp.vfc_typenum = vfsp->vfc_typenum;
        xvfsp.vfc_refcount = vfsp->vfc_refcount;
        xvfsp.vfc_flags = vfsp->vfc_flags;
        return (SYSCTL_OUT(req, &xvfsp, sizeof(xvfsp)));
}
#endif

/*
 * Top level filesystem related information gathering.
 */
static int
sysctl_vfs_conflist(SYSCTL_HANDLER_ARGS)
{
        struct vfsconf *vfsp;
        int error;

        error = 0;
        vfsconf_slock();
        TAILQ_FOREACH(vfsp, &vfsconf, vfc_list) {
#ifdef COMPAT_FREEBSD32
                if (req->flags & SCTL_MASK32)
                        error = vfsconf2x32(req, vfsp);
                else
#endif
                        error = vfsconf2x(req, vfsp);
                if (error)
                        break;
        }
        vfsconf_sunlock();
        return (error);
}

SYSCTL_PROC(_vfs, OID_AUTO, conflist, CTLTYPE_OPAQUE | CTLFLAG_RD |
    CTLFLAG_MPSAFE, NULL, 0, sysctl_vfs_conflist,
    "S,xvfsconf", "List of all configured filesystems");

#ifndef BURN_BRIDGES
static int      sysctl_ovfs_conf(SYSCTL_HANDLER_ARGS);

static int
vfs_sysctl(SYSCTL_HANDLER_ARGS)
{
        int *name = (int *)arg1 - 1;    /* XXX */
        u_int namelen = arg2 + 1;       /* XXX */
        struct vfsconf *vfsp;

        log(LOG_WARNING, "userland calling deprecated sysctl, "
            "please rebuild world\n");

#if 1 || defined(COMPAT_PRELITE2)
        /* Resolve ambiguity between VFS_VFSCONF and VFS_GENERIC. */
        if (namelen == 1)
                return (sysctl_ovfs_conf(oidp, arg1, arg2, req));
#endif

        switch (name[1]) {
        case VFS_MAXTYPENUM:
                if (namelen != 2)
                        return (ENOTDIR);
                return (SYSCTL_OUT(req, &maxvfsconf, sizeof(int)));
        case VFS_CONF:
                if (namelen != 3)
                        return (ENOTDIR);       /* overloaded */
                vfsconf_slock();
                TAILQ_FOREACH(vfsp, &vfsconf, vfc_list) {
                        if (vfsp->vfc_typenum == name[2])
                                break;
                }
                vfsconf_sunlock();
                if (vfsp == NULL)
                        return (EOPNOTSUPP);
#ifdef COMPAT_FREEBSD32
                if (req->flags & SCTL_MASK32)
                        return (vfsconf2x32(req, vfsp));
                else
#endif
                        return (vfsconf2x(req, vfsp));
        }
        return (EOPNOTSUPP);
}

static SYSCTL_NODE(_vfs, VFS_GENERIC, generic, CTLFLAG_RD | CTLFLAG_SKIP |
    CTLFLAG_MPSAFE, vfs_sysctl,
    "Generic filesystem");

#if 1 || defined(COMPAT_PRELITE2)

static int
sysctl_ovfs_conf(SYSCTL_HANDLER_ARGS)
{
        int error;
        struct vfsconf *vfsp;
        struct ovfsconf ovfs;

        vfsconf_slock();
        TAILQ_FOREACH(vfsp, &vfsconf, vfc_list) {
                bzero(&ovfs, sizeof(ovfs));
                ovfs.vfc_vfsops = vfsp->vfc_vfsops;     /* XXX used as flag */
                strcpy(ovfs.vfc_name, vfsp->vfc_name);
                ovfs.vfc_index = vfsp->vfc_typenum;
                ovfs.vfc_refcount = vfsp->vfc_refcount;
                ovfs.vfc_flags = vfsp->vfc_flags;
                error = SYSCTL_OUT(req, &ovfs, sizeof ovfs);
                if (error != 0) {
                        vfsconf_sunlock();
                        return (error);
                }
        }
        vfsconf_sunlock();
        return (0);
}

#endif /* 1 || COMPAT_PRELITE2 */
#endif /* !BURN_BRIDGES */

#define KINFO_VNODESLOP         10
#ifdef notyet
/*
 * Dump vnode list (via sysctl).
 */
/* ARGSUSED */
static int
sysctl_vnode(SYSCTL_HANDLER_ARGS)
{
        struct xvnode *xvn;
        struct mount *mp;
        struct vnode *vp;
        int error, len, n;

        /*
         * Stale numvnodes access is not fatal here.
         */
        req->lock = 0;
        len = (numvnodes + KINFO_VNODESLOP) * sizeof *xvn;
        if (!req->oldptr)
                /* Make an estimate */
                return (SYSCTL_OUT(req, 0, len));

        error = sysctl_wire_old_buffer(req, 0);
        if (error != 0)
                return (error);
        xvn = malloc(len, M_TEMP, M_ZERO | M_WAITOK);
        n = 0;
        mtx_lock(&mountlist_mtx);
        TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                if (vfs_busy(mp, MBF_NOWAIT | MBF_MNTLSTLOCK))
                        continue;
                MNT_ILOCK(mp);
                TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                        if (n == len)
                                break;
                        vref(vp);
                        xvn[n].xv_size = sizeof *xvn;
                        xvn[n].xv_vnode = vp;
                        xvn[n].xv_id = 0;       /* XXX compat */
#define XV_COPY(field) xvn[n].xv_##field = vp->v_##field
                        XV_COPY(usecount);
                        XV_COPY(writecount);
                        XV_COPY(holdcnt);
                        XV_COPY(mount);
                        XV_COPY(numoutput);
                        XV_COPY(type);
#undef XV_COPY
                        xvn[n].xv_flag = vp->v_vflag;

                        switch (vp->v_type) {
                        case VREG:
                        case VDIR:
                        case VLNK:
                                break;
                        case VBLK:
                        case VCHR:
                                if (vp->v_rdev == NULL) {
                                        vrele(vp);
                                        continue;
                                }
                                xvn[n].xv_dev = dev2udev(vp->v_rdev);
                                break;
                        case VSOCK:
                                xvn[n].xv_socket = vp->v_socket;
                                break;
                        case VFIFO:
                                xvn[n].xv_fifo = vp->v_fifoinfo;
                                break;
                        case VNON:
                        case VBAD:
                        default:
                                /* shouldn't happen? */
                                vrele(vp);
                                continue;
                        }
                        vrele(vp);
                        ++n;
                }
                MNT_IUNLOCK(mp);
                mtx_lock(&mountlist_mtx);
                vfs_unbusy(mp);
                if (n == len)
                        break;
        }
        mtx_unlock(&mountlist_mtx);

        error = SYSCTL_OUT(req, xvn, n * sizeof *xvn);
        free(xvn, M_TEMP);
        return (error);
}

SYSCTL_PROC(_kern, KERN_VNODE, vnode, CTLTYPE_OPAQUE | CTLFLAG_RD |
    CTLFLAG_MPSAFE, 0, 0, sysctl_vnode, "S,xvnode",
    "");
#endif

static void
unmount_or_warn(struct mount *mp)
{
        int error;

        error = dounmount(mp, MNT_FORCE, curthread);
        if (error != 0) {
                printf("unmount of %s failed (", mp->mnt_stat.f_mntonname);
                if (error == EBUSY)
                        printf("BUSY)\n");
                else
                        printf("%d)\n", error);
        }
}

/*
 * Unmount all filesystems. The list is traversed in reverse order
 * of mounting to avoid dependencies.
 */
void
vfs_unmountall(void)
{
        struct mount *mp, *tmp;

        CTR1(KTR_VFS, "%s: unmounting all filesystems", __func__);

        /*
         * Since this only runs when rebooting, it is not interlocked.
         */
        TAILQ_FOREACH_REVERSE_SAFE(mp, &mountlist, mntlist, mnt_list, tmp) {
                vfs_ref(mp);

                /*
                 * Forcibly unmounting "/dev" before "/" would prevent clean
                 * unmount of the latter.
                 */
                if (mp == rootdevmp)
                        continue;

                unmount_or_warn(mp);
        }

        if (rootdevmp != NULL)
                unmount_or_warn(rootdevmp);
}

static void
vfs_deferred_inactive(struct vnode *vp, int lkflags)
{

        ASSERT_VI_LOCKED(vp, __func__);
        VNASSERT((vp->v_iflag & VI_DEFINACT) == 0, vp, ("VI_DEFINACT still set"));
        if ((vp->v_iflag & VI_OWEINACT) == 0) {
                vdropl(vp);
                return;
        }
        if (vn_lock(vp, lkflags) == 0) {
                VI_LOCK(vp);
                vinactive(vp);
                VOP_UNLOCK(vp);
                vdropl(vp);
                return;
        }
        vdefer_inactive_unlocked(vp);
}

static int
vfs_periodic_inactive_filter(struct vnode *vp, void *arg)
{

        return (vp->v_iflag & VI_DEFINACT);
}

static void __noinline
vfs_periodic_inactive(struct mount *mp, int flags)
{
        struct vnode *vp, *mvp;
        int lkflags;

        lkflags = LK_EXCLUSIVE | LK_INTERLOCK;
        if (flags != MNT_WAIT)
                lkflags |= LK_NOWAIT;

        MNT_VNODE_FOREACH_LAZY(vp, mp, mvp, vfs_periodic_inactive_filter, NULL) {
                if ((vp->v_iflag & VI_DEFINACT) == 0) {
                        VI_UNLOCK(vp);
                        continue;
                }
                vp->v_iflag &= ~VI_DEFINACT;
                vfs_deferred_inactive(vp, lkflags);
        }
}

static inline bool
vfs_want_msync(struct vnode *vp)
{
        struct vm_object *obj;

        /*
         * This test may be performed without any locks held.
         * We rely on vm_object's type stability.
         */
        if (vp->v_vflag & VV_NOSYNC)
                return (false);
        obj = vp->v_object;
        return (obj != NULL && vm_object_mightbedirty(obj));
}

static int
vfs_periodic_msync_inactive_filter(struct vnode *vp, void *arg __unused)
{

        if (vp->v_vflag & VV_NOSYNC)
                return (false);
        if (vp->v_iflag & VI_DEFINACT)
                return (true);
        return (vfs_want_msync(vp));
}

static void __noinline
vfs_periodic_msync_inactive(struct mount *mp, int flags)
{
        struct vnode *vp, *mvp;
        struct vm_object *obj;
        struct thread *td;
        int lkflags, objflags;
        bool seen_defer;

        td = curthread;

        lkflags = LK_EXCLUSIVE | LK_INTERLOCK;
        if (flags != MNT_WAIT) {
                lkflags |= LK_NOWAIT;
                objflags = OBJPC_NOSYNC;
        } else {
                objflags = OBJPC_SYNC;
        }

        MNT_VNODE_FOREACH_LAZY(vp, mp, mvp, vfs_periodic_msync_inactive_filter, NULL) {
                seen_defer = false;
                if (vp->v_iflag & VI_DEFINACT) {
                        vp->v_iflag &= ~VI_DEFINACT;
                        seen_defer = true;
                }
                if (!vfs_want_msync(vp)) {
                        if (seen_defer)
                                vfs_deferred_inactive(vp, lkflags);
                        else
                                VI_UNLOCK(vp);
                        continue;
                }
                if (vget(vp, lkflags, td) == 0) {
                        obj = vp->v_object;
                        if (obj != NULL && (vp->v_vflag & VV_NOSYNC) == 0) {
                                VM_OBJECT_WLOCK(obj);
                                vm_object_page_clean(obj, 0, 0, objflags);
                                VM_OBJECT_WUNLOCK(obj);
                        }
                        vput(vp);
                        if (seen_defer)
                                vdrop(vp);
                } else {
                        if (seen_defer)
                                vdefer_inactive_unlocked(vp);
                }
        }
}

void
vfs_periodic(struct mount *mp, int flags)
{

        CTR2(KTR_VFS, "%s: mp %p", __func__, mp);

        if ((mp->mnt_kern_flag & MNTK_NOMSYNC) != 0)
                vfs_periodic_inactive(mp, flags);
        else
                vfs_periodic_msync_inactive(mp, flags);
}

static void
destroy_vpollinfo_free(struct vpollinfo *vi)
{

        knlist_destroy(&vi->vpi_selinfo.si_note);
        mtx_destroy(&vi->vpi_lock);
        uma_zfree(vnodepoll_zone, vi);
}

static void
destroy_vpollinfo(struct vpollinfo *vi)
{

        knlist_clear(&vi->vpi_selinfo.si_note, 1);
        seldrain(&vi->vpi_selinfo);
        destroy_vpollinfo_free(vi);
}

/*
 * Initialize per-vnode helper structure to hold poll-related state.
 */
void
v_addpollinfo(struct vnode *vp)
{
        struct vpollinfo *vi;

        if (vp->v_pollinfo != NULL)
                return;
        vi = uma_zalloc(vnodepoll_zone, M_WAITOK | M_ZERO);
        mtx_init(&vi->vpi_lock, "vnode pollinfo", NULL, MTX_DEF);
        knlist_init(&vi->vpi_selinfo.si_note, vp, vfs_knllock,
            vfs_knlunlock, vfs_knl_assert_locked, vfs_knl_assert_unlocked);
        VI_LOCK(vp);
        if (vp->v_pollinfo != NULL) {
                VI_UNLOCK(vp);
                destroy_vpollinfo_free(vi);
                return;
        }
        vp->v_pollinfo = vi;
        VI_UNLOCK(vp);
}

/*
 * Record a process's interest in events which might happen to
 * a vnode.  Because poll uses the historic select-style interface
 * internally, this routine serves as both the ``check for any
 * pending events'' and the ``record my interest in future events''
 * functions.  (These are done together, while the lock is held,
 * to avoid race conditions.)
 */
int
vn_pollrecord(struct vnode *vp, struct thread *td, int events)
{

        v_addpollinfo(vp);
        mtx_lock(&vp->v_pollinfo->vpi_lock);
        if (vp->v_pollinfo->vpi_revents & events) {
                /*
                 * This leaves events we are not interested
                 * in available for the other process which
                 * which presumably had requested them
                 * (otherwise they would never have been
                 * recorded).
                 */
                events &= vp->v_pollinfo->vpi_revents;
                vp->v_pollinfo->vpi_revents &= ~events;

                mtx_unlock(&vp->v_pollinfo->vpi_lock);
                return (events);
        }
        vp->v_pollinfo->vpi_events |= events;
        selrecord(td, &vp->v_pollinfo->vpi_selinfo);
        mtx_unlock(&vp->v_pollinfo->vpi_lock);
        return (0);
}

/*
 * Routine to create and manage a filesystem syncer vnode.
 */
#define sync_close ((int (*)(struct  vop_close_args *))nullop)
static int      sync_fsync(struct  vop_fsync_args *);
static int      sync_inactive(struct  vop_inactive_args *);
static int      sync_reclaim(struct  vop_reclaim_args *);

static struct vop_vector sync_vnodeops = {
        .vop_bypass =   VOP_EOPNOTSUPP,
        .vop_close =    sync_close,             /* close */
        .vop_fsync =    sync_fsync,             /* fsync */
        .vop_inactive = sync_inactive,  /* inactive */
        .vop_need_inactive = vop_stdneed_inactive, /* need_inactive */
        .vop_reclaim =  sync_reclaim,   /* reclaim */
        .vop_lock1 =    vop_stdlock,    /* lock */
        .vop_unlock =   vop_stdunlock,  /* unlock */
        .vop_islocked = vop_stdislocked,        /* islocked */
};
VFS_VOP_VECTOR_REGISTER(sync_vnodeops);

/*
 * Create a new filesystem syncer vnode for the specified mount point.
 */
void
vfs_allocate_syncvnode(struct mount *mp)
{
        struct vnode *vp;
        struct bufobj *bo;
        static long start, incr, next;
        int error;

        /* Allocate a new vnode */
        error = getnewvnode("syncer", mp, &sync_vnodeops, &vp);
        if (error != 0)
                panic("vfs_allocate_syncvnode: getnewvnode() failed");
        vp->v_type = VNON;
        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
        vp->v_vflag |= VV_FORCEINSMQ;
        error = insmntque(vp, mp);
        if (error != 0)
                panic("vfs_allocate_syncvnode: insmntque() failed");
        vp->v_vflag &= ~VV_FORCEINSMQ;
        VOP_UNLOCK(vp);
        /*
         * Place the vnode onto the syncer worklist. We attempt to
         * scatter them about on the list so that they will go off
         * at evenly distributed times even if all the filesystems
         * are mounted at once.
         */
        next += incr;
        if (next == 0 || next > syncer_maxdelay) {
                start /= 2;
                incr /= 2;
                if (start == 0) {
                        start = syncer_maxdelay / 2;
                        incr = syncer_maxdelay;
                }
                next = start;
        }
        bo = &vp->v_bufobj;
        BO_LOCK(bo);
        vn_syncer_add_to_worklist(bo, syncdelay > 0 ? next % syncdelay : 0);
        /* XXX - vn_syncer_add_to_worklist() also grabs and drops sync_mtx. */
        mtx_lock(&sync_mtx);
        sync_vnode_count++;
        if (mp->mnt_syncer == NULL) {
                mp->mnt_syncer = vp;
                vp = NULL;
        }
        mtx_unlock(&sync_mtx);
        BO_UNLOCK(bo);
        if (vp != NULL) {
                vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
                vgone(vp);
                vput(vp);
        }
}

void
vfs_deallocate_syncvnode(struct mount *mp)
{
        struct vnode *vp;

        mtx_lock(&sync_mtx);
        vp = mp->mnt_syncer;
        if (vp != NULL)
                mp->mnt_syncer = NULL;
        mtx_unlock(&sync_mtx);
        if (vp != NULL)
                vrele(vp);
}

/*
 * Do a lazy sync of the filesystem.
 */
static int
sync_fsync(struct vop_fsync_args *ap)
{
        struct vnode *syncvp = ap->a_vp;
        struct mount *mp = syncvp->v_mount;
        int error, save;
        struct bufobj *bo;

        /*
         * We only need to do something if this is a lazy evaluation.
         */
        if (ap->a_waitfor != MNT_LAZY)
                return (0);

        /*
         * Move ourselves to the back of the sync list.
         */
        bo = &syncvp->v_bufobj;
        BO_LOCK(bo);
        vn_syncer_add_to_worklist(bo, syncdelay);
        BO_UNLOCK(bo);

        /*
         * Walk the list of vnodes pushing all that are dirty and
         * not already on the sync list.
         */
        if (vfs_busy(mp, MBF_NOWAIT) != 0)
                return (0);
        if (vn_start_write(NULL, &mp, V_NOWAIT) != 0) {
                vfs_unbusy(mp);
                return (0);
        }
        save = curthread_pflags_set(TDP_SYNCIO);
        /*
         * The filesystem at hand may be idle with free vnodes stored in the
         * batch.  Return them instead of letting them stay there indefinitely.
         */
        vfs_periodic(mp, MNT_NOWAIT);
        error = VFS_SYNC(mp, MNT_LAZY);
        curthread_pflags_restore(save);
        vn_finished_write(mp);
        vfs_unbusy(mp);
        return (error);
}

/*
 * The syncer vnode is no referenced.
 */
static int
sync_inactive(struct vop_inactive_args *ap)
{

        vgone(ap->a_vp);
        return (0);
}

/*
 * The syncer vnode is no longer needed and is being decommissioned.
 *
 * Modifications to the worklist must be protected by sync_mtx.
 */
static int
sync_reclaim(struct vop_reclaim_args *ap)
{
        struct vnode *vp = ap->a_vp;
        struct bufobj *bo;

        bo = &vp->v_bufobj;
        BO_LOCK(bo);
        mtx_lock(&sync_mtx);
        if (vp->v_mount->mnt_syncer == vp)
                vp->v_mount->mnt_syncer = NULL;
        if (bo->bo_flag & BO_ONWORKLST) {
                LIST_REMOVE(bo, bo_synclist);
                syncer_worklist_len--;
                sync_vnode_count--;
                bo->bo_flag &= ~BO_ONWORKLST;
        }
        mtx_unlock(&sync_mtx);
        BO_UNLOCK(bo);

        return (0);
}

int
vn_need_pageq_flush(struct vnode *vp)
{
        struct vm_object *obj;
        int need;

        MPASS(mtx_owned(VI_MTX(vp)));
        need = 0;
        if ((obj = vp->v_object) != NULL && (vp->v_vflag & VV_NOSYNC) == 0 &&
            vm_object_mightbedirty(obj))
                need = 1;
        return (need);
}

/*
 * Check if vnode represents a disk device
 */
int
vn_isdisk(struct vnode *vp, int *errp)
{
        int error;

        if (vp->v_type != VCHR) {
                error = ENOTBLK;
                goto out;
        }
        error = 0;
        dev_lock();
        if (vp->v_rdev == NULL)
                error = ENXIO;
        else if (vp->v_rdev->si_devsw == NULL)
                error = ENXIO;
        else if (!(vp->v_rdev->si_devsw->d_flags & D_DISK))
                error = ENOTBLK;
        dev_unlock();
out:
        if (errp != NULL)
                *errp = error;
        return (error == 0);
}

/*
 * Common filesystem object access control check routine.  Accepts a
 * vnode's type, "mode", uid and gid, requested access mode, credentials,
 * and optional call-by-reference privused argument allowing vaccess()
 * to indicate to the caller whether privilege was used to satisfy the
 * request (obsoleted).  Returns 0 on success, or an errno on failure.
 */
int
vaccess(enum vtype type, mode_t file_mode, uid_t file_uid, gid_t file_gid,
    accmode_t accmode, struct ucred *cred, int *privused)
{
        accmode_t dac_granted;
        accmode_t priv_granted;

        KASSERT((accmode & ~(VEXEC | VWRITE | VREAD | VADMIN | VAPPEND)) == 0,
            ("invalid bit in accmode"));
        KASSERT((accmode & VAPPEND) == 0 || (accmode & VWRITE),
            ("VAPPEND without VWRITE"));

        /*
         * Look for a normal, non-privileged way to access the file/directory
         * as requested.  If it exists, go with that.
         */

        if (privused != NULL)
                *privused = 0;

        dac_granted = 0;

        /* Check the owner. */
        if (cred->cr_uid == file_uid) {
                dac_granted |= VADMIN;
                if (file_mode & S_IXUSR)
                        dac_granted |= VEXEC;
                if (file_mode & S_IRUSR)
                        dac_granted |= VREAD;
                if (file_mode & S_IWUSR)
                        dac_granted |= (VWRITE | VAPPEND);

                if ((accmode & dac_granted) == accmode)
                        return (0);

                goto privcheck;
        }

        /* Otherwise, check the groups (first match) */
        if (groupmember(file_gid, cred)) {
                if (file_mode & S_IXGRP)
                        dac_granted |= VEXEC;
                if (file_mode & S_IRGRP)
                        dac_granted |= VREAD;
                if (file_mode & S_IWGRP)
                        dac_granted |= (VWRITE | VAPPEND);

                if ((accmode & dac_granted) == accmode)
                        return (0);

                goto privcheck;
        }

        /* Otherwise, check everyone else. */
        if (file_mode & S_IXOTH)
                dac_granted |= VEXEC;
        if (file_mode & S_IROTH)
                dac_granted |= VREAD;
        if (file_mode & S_IWOTH)
                dac_granted |= (VWRITE | VAPPEND);
        if ((accmode & dac_granted) == accmode)
                return (0);

privcheck:
        /*
         * Build a privilege mask to determine if the set of privileges
         * satisfies the requirements when combined with the granted mask
         * from above.  For each privilege, if the privilege is required,
         * bitwise or the request type onto the priv_granted mask.
         */
        priv_granted = 0;

        if (type == VDIR) {
                /*
                 * For directories, use PRIV_VFS_LOOKUP to satisfy VEXEC
                 * requests, instead of PRIV_VFS_EXEC.
                 */
                if ((accmode & VEXEC) && ((dac_granted & VEXEC) == 0) &&
                    !priv_check_cred(cred, PRIV_VFS_LOOKUP))
                        priv_granted |= VEXEC;
        } else {
                /*
                 * Ensure that at least one execute bit is on. Otherwise,
                 * a privileged user will always succeed, and we don't want
                 * this to happen unless the file really is executable.
                 */
                if ((accmode & VEXEC) && ((dac_granted & VEXEC) == 0) &&
                    (file_mode & (S_IXUSR | S_IXGRP | S_IXOTH)) != 0 &&
                    !priv_check_cred(cred, PRIV_VFS_EXEC))
                        priv_granted |= VEXEC;
        }

        if ((accmode & VREAD) && ((dac_granted & VREAD) == 0) &&
            !priv_check_cred(cred, PRIV_VFS_READ))
                priv_granted |= VREAD;

        if ((accmode & VWRITE) && ((dac_granted & VWRITE) == 0) &&
            !priv_check_cred(cred, PRIV_VFS_WRITE))
                priv_granted |= (VWRITE | VAPPEND);

        if ((accmode & VADMIN) && ((dac_granted & VADMIN) == 0) &&
            !priv_check_cred(cred, PRIV_VFS_ADMIN))
                priv_granted |= VADMIN;

        if ((accmode & (priv_granted | dac_granted)) == accmode) {
                /* XXX audit: privilege used */
                if (privused != NULL)
                        *privused = 1;
                return (0);
        }

        return ((accmode & VADMIN) ? EPERM : EACCES);
}

/*
 * Credential check based on process requesting service, and per-attribute
 * permissions.
 */
int
extattr_check_cred(struct vnode *vp, int attrnamespace, struct ucred *cred,
    struct thread *td, accmode_t accmode)
{

        /*
         * Kernel-invoked always succeeds.
         */
        if (cred == NOCRED)
                return (0);

        /*
         * Do not allow privileged processes in jail to directly manipulate
         * system attributes.
         */
        switch (attrnamespace) {
        case EXTATTR_NAMESPACE_SYSTEM:
                /* Potentially should be: return (EPERM); */
                return (priv_check_cred(cred, PRIV_VFS_EXTATTR_SYSTEM));
        case EXTATTR_NAMESPACE_USER:
                return (VOP_ACCESS(vp, accmode, cred, td));
        default:
                return (EPERM);
        }
}

#ifdef DEBUG_VFS_LOCKS
/*
 * This only exists to suppress warnings from unlocked specfs accesses.  It is
 * no longer ok to have an unlocked VFS.
 */
#define IGNORE_LOCK(vp) (KERNEL_PANICKED() || (vp) == NULL ||           \
        (vp)->v_type == VCHR || (vp)->v_type == VBAD)

int vfs_badlock_ddb = 1;        /* Drop into debugger on violation. */
SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_ddb, CTLFLAG_RW, &vfs_badlock_ddb, 0,
    "Drop into debugger on lock violation");

int vfs_badlock_mutex = 1;      /* Check for interlock across VOPs. */
SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_mutex, CTLFLAG_RW, &vfs_badlock_mutex,
    0, "Check for interlock across VOPs");

int vfs_badlock_print = 1;      /* Print lock violations. */
SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_print, CTLFLAG_RW, &vfs_badlock_print,
    0, "Print lock violations");

int vfs_badlock_vnode = 1;      /* Print vnode details on lock violations. */
SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_vnode, CTLFLAG_RW, &vfs_badlock_vnode,
    0, "Print vnode details on lock violations");

#ifdef KDB
int vfs_badlock_backtrace = 1;  /* Print backtrace at lock violations. */
SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_backtrace, CTLFLAG_RW,
    &vfs_badlock_backtrace, 0, "Print backtrace at lock violations");
#endif

static void
vfs_badlock(const char *msg, const char *str, struct vnode *vp)
{

#ifdef KDB
        if (vfs_badlock_backtrace)
                kdb_backtrace();
#endif
        if (vfs_badlock_vnode)
                vn_printf(vp, "vnode ");
        if (vfs_badlock_print)
                printf("%s: %p %s\n", str, (void *)vp, msg);
        if (vfs_badlock_ddb)
                kdb_enter(KDB_WHY_VFSLOCK, "lock violation");
}

void
assert_vi_locked(struct vnode *vp, const char *str)
{

        if (vfs_badlock_mutex && !mtx_owned(VI_MTX(vp)))
                vfs_badlock("interlock is not locked but should be", str, vp);
}

void
assert_vi_unlocked(struct vnode *vp, const char *str)
{

        if (vfs_badlock_mutex && mtx_owned(VI_MTX(vp)))
                vfs_badlock("interlock is locked but should not be", str, vp);
}

void
assert_vop_locked(struct vnode *vp, const char *str)
{
        int locked;

        if (!IGNORE_LOCK(vp)) {
                locked = VOP_ISLOCKED(vp);
                if (locked == 0 || locked == LK_EXCLOTHER)
                        vfs_badlock("is not locked but should be", str, vp);
        }
}

void
assert_vop_unlocked(struct vnode *vp, const char *str)
{

        if (!IGNORE_LOCK(vp) && VOP_ISLOCKED(vp) == LK_EXCLUSIVE)
                vfs_badlock("is locked but should not be", str, vp);
}

void
assert_vop_elocked(struct vnode *vp, const char *str)
{

        if (!IGNORE_LOCK(vp) && VOP_ISLOCKED(vp) != LK_EXCLUSIVE)
                vfs_badlock("is not exclusive locked but should be", str, vp);
}
#endif /* DEBUG_VFS_LOCKS */

void
vop_rename_fail(struct vop_rename_args *ap)
{

        if (ap->a_tvp != NULL)
                vput(ap->a_tvp);
        if (ap->a_tdvp == ap->a_tvp)
                vrele(ap->a_tdvp);
        else
                vput(ap->a_tdvp);
        vrele(ap->a_fdvp);
        vrele(ap->a_fvp);
}

void
vop_rename_pre(void *ap)
{
        struct vop_rename_args *a = ap;

#ifdef DEBUG_VFS_LOCKS
        if (a->a_tvp)
                ASSERT_VI_UNLOCKED(a->a_tvp, "VOP_RENAME");
        ASSERT_VI_UNLOCKED(a->a_tdvp, "VOP_RENAME");
        ASSERT_VI_UNLOCKED(a->a_fvp, "VOP_RENAME");
        ASSERT_VI_UNLOCKED(a->a_fdvp, "VOP_RENAME");

        /* Check the source (from). */
        if (a->a_tdvp->v_vnlock != a->a_fdvp->v_vnlock &&
            (a->a_tvp == NULL || a->a_tvp->v_vnlock != a->a_fdvp->v_vnlock))
                ASSERT_VOP_UNLOCKED(a->a_fdvp, "vop_rename: fdvp locked");
        if (a->a_tvp == NULL || a->a_tvp->v_vnlock != a->a_fvp->v_vnlock)
                ASSERT_VOP_UNLOCKED(a->a_fvp, "vop_rename: fvp locked");

        /* Check the target. */
        if (a->a_tvp)
                ASSERT_VOP_LOCKED(a->a_tvp, "vop_rename: tvp not locked");
        ASSERT_VOP_LOCKED(a->a_tdvp, "vop_rename: tdvp not locked");
#endif
        if (a->a_tdvp != a->a_fdvp)
                vhold(a->a_fdvp);
        if (a->a_tvp != a->a_fvp)
                vhold(a->a_fvp);
        vhold(a->a_tdvp);
        if (a->a_tvp)
                vhold(a->a_tvp);
}

#ifdef DEBUG_VFS_LOCKS
void
vop_strategy_pre(void *ap)
{
        struct vop_strategy_args *a;
        struct buf *bp;

        a = ap;
        bp = a->a_bp;

        /*
         * Cluster ops lock their component buffers but not the IO container.
         */
        if ((bp->b_flags & B_CLUSTER) != 0)
                return;

        if (!KERNEL_PANICKED() && !BUF_ISLOCKED(bp)) {
                if (vfs_badlock_print)
                        printf(
                            "VOP_STRATEGY: bp is not locked but should be\n");
                if (vfs_badlock_ddb)
                        kdb_enter(KDB_WHY_VFSLOCK, "lock violation");
        }
}

void
vop_lock_pre(void *ap)
{
        struct vop_lock1_args *a = ap;

        if ((a->a_flags & LK_INTERLOCK) == 0)
                ASSERT_VI_UNLOCKED(a->a_vp, "VOP_LOCK");
        else
                ASSERT_VI_LOCKED(a->a_vp, "VOP_LOCK");
}

void
vop_lock_post(void *ap, int rc)
{
        struct vop_lock1_args *a = ap;

        ASSERT_VI_UNLOCKED(a->a_vp, "VOP_LOCK");
        if (rc == 0 && (a->a_flags & LK_EXCLOTHER) == 0)
                ASSERT_VOP_LOCKED(a->a_vp, "VOP_LOCK");
}

void
vop_unlock_pre(void *ap)
{
        struct vop_unlock_args *a = ap;

        ASSERT_VOP_LOCKED(a->a_vp, "VOP_UNLOCK");
}

void
vop_unlock_post(void *ap, int rc)
{
        return;
}

void
vop_need_inactive_pre(void *ap)
{
        struct vop_need_inactive_args *a = ap;

        ASSERT_VI_LOCKED(a->a_vp, "VOP_NEED_INACTIVE");
}

void
vop_need_inactive_post(void *ap, int rc)
{
        struct vop_need_inactive_args *a = ap;

        ASSERT_VI_LOCKED(a->a_vp, "VOP_NEED_INACTIVE");
}
#endif

void
vop_create_post(void *ap, int rc)
{
        struct vop_create_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_dvp, NOTE_WRITE);
}

void
vop_deleteextattr_post(void *ap, int rc)
{
        struct vop_deleteextattr_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_ATTRIB);
}

void
vop_link_post(void *ap, int rc)
{
        struct vop_link_args *a = ap;

        if (!rc) {
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_LINK);
                VFS_KNOTE_LOCKED(a->a_tdvp, NOTE_WRITE);
        }
}

void
vop_mkdir_post(void *ap, int rc)
{
        struct vop_mkdir_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_dvp, NOTE_WRITE | NOTE_LINK);
}

void
vop_mknod_post(void *ap, int rc)
{
        struct vop_mknod_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_dvp, NOTE_WRITE);
}

void
vop_reclaim_post(void *ap, int rc)
{
        struct vop_reclaim_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_REVOKE);
}

void
vop_remove_post(void *ap, int rc)
{
        struct vop_remove_args *a = ap;

        if (!rc) {
                VFS_KNOTE_LOCKED(a->a_dvp, NOTE_WRITE);
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_DELETE);
        }
}

void
vop_rename_post(void *ap, int rc)
{
        struct vop_rename_args *a = ap;
        long hint;

        if (!rc) {
                hint = NOTE_WRITE;
                if (a->a_fdvp == a->a_tdvp) {
                        if (a->a_tvp != NULL && a->a_tvp->v_type == VDIR)
                                hint |= NOTE_LINK;
                        VFS_KNOTE_UNLOCKED(a->a_fdvp, hint);
                        VFS_KNOTE_UNLOCKED(a->a_tdvp, hint);
                } else {
                        hint |= NOTE_EXTEND;
                        if (a->a_fvp->v_type == VDIR)
                                hint |= NOTE_LINK;
                        VFS_KNOTE_UNLOCKED(a->a_fdvp, hint);

                        if (a->a_fvp->v_type == VDIR && a->a_tvp != NULL &&
                            a->a_tvp->v_type == VDIR)
                                hint &= ~NOTE_LINK;
                        VFS_KNOTE_UNLOCKED(a->a_tdvp, hint);
                }

                VFS_KNOTE_UNLOCKED(a->a_fvp, NOTE_RENAME);
                if (a->a_tvp)
                        VFS_KNOTE_UNLOCKED(a->a_tvp, NOTE_DELETE);
        }
        if (a->a_tdvp != a->a_fdvp)
                vdrop(a->a_fdvp);
        if (a->a_tvp != a->a_fvp)
                vdrop(a->a_fvp);
        vdrop(a->a_tdvp);
        if (a->a_tvp)
                vdrop(a->a_tvp);
}

void
vop_rmdir_post(void *ap, int rc)
{
        struct vop_rmdir_args *a = ap;

        if (!rc) {
                VFS_KNOTE_LOCKED(a->a_dvp, NOTE_WRITE | NOTE_LINK);
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_DELETE);
        }
}

void
vop_setattr_post(void *ap, int rc)
{
        struct vop_setattr_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_ATTRIB);
}

void
vop_setextattr_post(void *ap, int rc)
{
        struct vop_setextattr_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_ATTRIB);
}

void
vop_symlink_post(void *ap, int rc)
{
        struct vop_symlink_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_dvp, NOTE_WRITE);
}

void
vop_open_post(void *ap, int rc)
{
        struct vop_open_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_OPEN);
}

void
vop_close_post(void *ap, int rc)
{
        struct vop_close_args *a = ap;

        if (!rc && (a->a_cred != NOCRED || /* filter out revokes */
            !VN_IS_DOOMED(a->a_vp))) {
                VFS_KNOTE_LOCKED(a->a_vp, (a->a_fflag & FWRITE) != 0 ?
                    NOTE_CLOSE_WRITE : NOTE_CLOSE);
        }
}

void
vop_read_post(void *ap, int rc)
{
        struct vop_read_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_READ);
}

void
vop_readdir_post(void *ap, int rc)
{
        struct vop_readdir_args *a = ap;

        if (!rc)
                VFS_KNOTE_LOCKED(a->a_vp, NOTE_READ);
}

static struct knlist fs_knlist;

static void
vfs_event_init(void *arg)
{
        knlist_init_mtx(&fs_knlist, NULL);
}
/* XXX - correct order? */
SYSINIT(vfs_knlist, SI_SUB_VFS, SI_ORDER_ANY, vfs_event_init, NULL);

void
vfs_event_signal(fsid_t *fsid, uint32_t event, intptr_t data __unused)
{

        KNOTE_UNLOCKED(&fs_knlist, event);
}

static int      filt_fsattach(struct knote *kn);
static void     filt_fsdetach(struct knote *kn);
static int      filt_fsevent(struct knote *kn, long hint);

struct filterops fs_filtops = {
        .f_isfd = 0,
        .f_attach = filt_fsattach,
        .f_detach = filt_fsdetach,
        .f_event = filt_fsevent
};

static int
filt_fsattach(struct knote *kn)
{

        kn->kn_flags |= EV_CLEAR;
        knlist_add(&fs_knlist, kn, 0);
        return (0);
}

static void
filt_fsdetach(struct knote *kn)
{

        knlist_remove(&fs_knlist, kn, 0);
}

static int
filt_fsevent(struct knote *kn, long hint)
{

        kn->kn_fflags |= hint;
        return (kn->kn_fflags != 0);
}

static int
sysctl_vfs_ctl(SYSCTL_HANDLER_ARGS)
{
        struct vfsidctl vc;
        int error;
        struct mount *mp;

        error = SYSCTL_IN(req, &vc, sizeof(vc));
        if (error)
                return (error);
        if (vc.vc_vers != VFS_CTL_VERS1)
                return (EINVAL);
        mp = vfs_getvfs(&vc.vc_fsid);
        if (mp == NULL)
                return (ENOENT);
        /* ensure that a specific sysctl goes to the right filesystem. */
        if (strcmp(vc.vc_fstypename, "*") != 0 &&
            strcmp(vc.vc_fstypename, mp->mnt_vfc->vfc_name) != 0) {
                vfs_rel(mp);
                return (EINVAL);
        }
        VCTLTOREQ(&vc, req);
        error = VFS_SYSCTL(mp, vc.vc_op, req);
        vfs_rel(mp);
        return (error);
}

SYSCTL_PROC(_vfs, OID_AUTO, ctl, CTLTYPE_OPAQUE | CTLFLAG_MPSAFE | CTLFLAG_WR,
    NULL, 0, sysctl_vfs_ctl, "",
    "Sysctl by fsid");

/*
 * Function to initialize a va_filerev field sensibly.
 * XXX: Wouldn't a random number make a lot more sense ??
 */
u_quad_t
init_va_filerev(void)
{
        struct bintime bt;

        getbinuptime(&bt);
        return (((u_quad_t)bt.sec << 32LL) | (bt.frac >> 32LL));
}

static int      filt_vfsread(struct knote *kn, long hint);
static int      filt_vfswrite(struct knote *kn, long hint);
static int      filt_vfsvnode(struct knote *kn, long hint);
static void     filt_vfsdetach(struct knote *kn);
static struct filterops vfsread_filtops = {
        .f_isfd = 1,
        .f_detach = filt_vfsdetach,
        .f_event = filt_vfsread
};
static struct filterops vfswrite_filtops = {
        .f_isfd = 1,
        .f_detach = filt_vfsdetach,
        .f_event = filt_vfswrite
};
static struct filterops vfsvnode_filtops = {
        .f_isfd = 1,
        .f_detach = filt_vfsdetach,
        .f_event = filt_vfsvnode
};

static void
vfs_knllock(void *arg)
{
        struct vnode *vp = arg;

        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
}

static void
vfs_knlunlock(void *arg)
{
        struct vnode *vp = arg;

        VOP_UNLOCK(vp);
}

static void
vfs_knl_assert_locked(void *arg)
{
#ifdef DEBUG_VFS_LOCKS
        struct vnode *vp = arg;

        ASSERT_VOP_LOCKED(vp, "vfs_knl_assert_locked");
#endif
}

static void
vfs_knl_assert_unlocked(void *arg)
{
#ifdef DEBUG_VFS_LOCKS
        struct vnode *vp = arg;

        ASSERT_VOP_UNLOCKED(vp, "vfs_knl_assert_unlocked");
#endif
}

int
vfs_kqfilter(struct vop_kqfilter_args *ap)
{
        struct vnode *vp = ap->a_vp;
        struct knote *kn = ap->a_kn;
        struct knlist *knl;

        switch (kn->kn_filter) {
        case EVFILT_READ:
                kn->kn_fop = &vfsread_filtops;
                break;
        case EVFILT_WRITE:
                kn->kn_fop = &vfswrite_filtops;
                break;
        case EVFILT_VNODE:
                kn->kn_fop = &vfsvnode_filtops;
                break;
        default:
                return (EINVAL);
        }

        kn->kn_hook = (caddr_t)vp;

        v_addpollinfo(vp);
        if (vp->v_pollinfo == NULL)
                return (ENOMEM);
        knl = &vp->v_pollinfo->vpi_selinfo.si_note;
        vhold(vp);
        knlist_add(knl, kn, 0);

        return (0);
}

/*
 * Detach knote from vnode
 */
static void
filt_vfsdetach(struct knote *kn)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;

        KASSERT(vp->v_pollinfo != NULL, ("Missing v_pollinfo"));
        knlist_remove(&vp->v_pollinfo->vpi_selinfo.si_note, kn, 0);
        vdrop(vp);
}

/*ARGSUSED*/
static int
filt_vfsread(struct knote *kn, long hint)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;
        struct vattr va;
        int res;

        /*
         * filesystem is gone, so set the EOF flag and schedule
         * the knote for deletion.
         */
        if (hint == NOTE_REVOKE || (hint == 0 && vp->v_type == VBAD)) {
                VI_LOCK(vp);
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);
                VI_UNLOCK(vp);
                return (1);
        }

        if (VOP_GETATTR(vp, &va, curthread->td_ucred))
                return (0);

        VI_LOCK(vp);
        kn->kn_data = va.va_size - kn->kn_fp->f_offset;
        res = (kn->kn_sfflags & NOTE_FILE_POLL) != 0 || kn->kn_data != 0;
        VI_UNLOCK(vp);
        return (res);
}

/*ARGSUSED*/
static int
filt_vfswrite(struct knote *kn, long hint)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;

        VI_LOCK(vp);

        /*
         * filesystem is gone, so set the EOF flag and schedule
         * the knote for deletion.
         */
        if (hint == NOTE_REVOKE || (hint == 0 && vp->v_type == VBAD))
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);

        kn->kn_data = 0;
        VI_UNLOCK(vp);
        return (1);
}

static int
filt_vfsvnode(struct knote *kn, long hint)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;
        int res;

        VI_LOCK(vp);
        if (kn->kn_sfflags & hint)
                kn->kn_fflags |= hint;
        if (hint == NOTE_REVOKE || (hint == 0 && vp->v_type == VBAD)) {
                kn->kn_flags |= EV_EOF;
                VI_UNLOCK(vp);
                return (1);
        }
        res = (kn->kn_fflags != 0);
        VI_UNLOCK(vp);
        return (res);
}

/*
 * Returns whether the directory is empty or not.
 * If it is empty, the return value is 0; otherwise
 * the return value is an error value (which may
 * be ENOTEMPTY).
 */
int
vfs_emptydir(struct vnode *vp)
{
        struct uio uio;
        struct iovec iov;
        struct dirent *dirent, *dp, *endp;
        int error, eof;

        error = 0;
        eof = 0;

        ASSERT_VOP_LOCKED(vp, "vfs_emptydir");

        dirent = malloc(sizeof(struct dirent), M_TEMP, M_WAITOK);
        iov.iov_base = dirent;
        iov.iov_len = sizeof(struct dirent);

        uio.uio_iov = &iov;
        uio.uio_iovcnt = 1;
        uio.uio_offset = 0;
        uio.uio_resid = sizeof(struct dirent);
        uio.uio_segflg = UIO_SYSSPACE;
        uio.uio_rw = UIO_READ;
        uio.uio_td = curthread;

        while (eof == 0 && error == 0) {
                error = VOP_READDIR(vp, &uio, curthread->td_ucred, &eof,
                    NULL, NULL);
                if (error != 0)
                        break;
                endp = (void *)((uint8_t *)dirent +
                    sizeof(struct dirent) - uio.uio_resid);
                for (dp = dirent; dp < endp;
                     dp = (void *)((uint8_t *)dp + GENERIC_DIRSIZ(dp))) {
                        if (dp->d_type == DT_WHT)
                                continue;
                        if (dp->d_namlen == 0)
                                continue;
                        if (dp->d_type != DT_DIR &&
                            dp->d_type != DT_UNKNOWN) {
                                error = ENOTEMPTY;
                                break;
                        }
                        if (dp->d_namlen > 2) {
                                error = ENOTEMPTY;
                                break;
                        }
                        if (dp->d_namlen == 1 &&
                            dp->d_name[0] != '.') {
                                error = ENOTEMPTY;
                                break;
                        }
                        if (dp->d_namlen == 2 &&
                            dp->d_name[1] != '.') {
                                error = ENOTEMPTY;
                                break;
                        }
                        uio.uio_resid = sizeof(struct dirent);
                }
        }
        free(dirent, M_TEMP);
        return (error);
}

int
vfs_read_dirent(struct vop_readdir_args *ap, struct dirent *dp, off_t off)
{
        int error;

        if (dp->d_reclen > ap->a_uio->uio_resid)
                return (ENAMETOOLONG);
        error = uiomove(dp, dp->d_reclen, ap->a_uio);
        if (error) {
                if (ap->a_ncookies != NULL) {
                        if (ap->a_cookies != NULL)
                                free(ap->a_cookies, M_TEMP);
                        ap->a_cookies = NULL;
                        *ap->a_ncookies = 0;
                }
                return (error);
        }
        if (ap->a_ncookies == NULL)
                return (0);

        KASSERT(ap->a_cookies,
            ("NULL ap->a_cookies value with non-NULL ap->a_ncookies!"));

        *ap->a_cookies = realloc(*ap->a_cookies,
            (*ap->a_ncookies + 1) * sizeof(u_long), M_TEMP, M_WAITOK | M_ZERO);
        (*ap->a_cookies)[*ap->a_ncookies] = off;
        *ap->a_ncookies += 1;
        return (0);
}

/*
 * Mark for update the access time of the file if the filesystem
 * supports VOP_MARKATIME.  This functionality is used by execve and
 * mmap, so we want to avoid the I/O implied by directly setting
 * va_atime for the sake of efficiency.
 */
void
vfs_mark_atime(struct vnode *vp, struct ucred *cred)
{
        struct mount *mp;

        mp = vp->v_mount;
        ASSERT_VOP_LOCKED(vp, "vfs_mark_atime");
        if (mp != NULL && (mp->mnt_flag & (MNT_NOATIME | MNT_RDONLY)) == 0)
                (void)VOP_MARKATIME(vp);
}

/*
 * The purpose of this routine is to remove granularity from accmode_t,
 * reducing it into standard unix access bits - VEXEC, VREAD, VWRITE,
 * VADMIN and VAPPEND.
 *
 * If it returns 0, the caller is supposed to continue with the usual
 * access checks using 'accmode' as modified by this routine.  If it
 * returns nonzero value, the caller is supposed to return that value
 * as errno.
 *
 * Note that after this routine runs, accmode may be zero.
 */
int
vfs_unixify_accmode(accmode_t *accmode)
{
        /*
         * There is no way to specify explicit "deny" rule using
         * file mode or POSIX.1e ACLs.
         */
        if (*accmode & VEXPLICIT_DENY) {
                *accmode = 0;
                return (0);
        }

        /*
         * None of these can be translated into usual access bits.
         * Also, the common case for NFSv4 ACLs is to not contain
         * either of these bits. Caller should check for VWRITE
         * on the containing directory instead.
         */
        if (*accmode & (VDELETE_CHILD | VDELETE))
                return (EPERM);

        if (*accmode & VADMIN_PERMS) {
                *accmode &= ~VADMIN_PERMS;
                *accmode |= VADMIN;
        }

        /*
         * There is no way to deny VREAD_ATTRIBUTES, VREAD_ACL
         * or VSYNCHRONIZE using file mode or POSIX.1e ACL.
         */
        *accmode &= ~(VSTAT_PERMS | VSYNCHRONIZE);

        return (0);
}

/*
 * Clear out a doomed vnode (if any) and replace it with a new one as long
 * as the fs is not being unmounted. Return the root vnode to the caller.
 */
static int __noinline
vfs_cache_root_fallback(struct mount *mp, int flags, struct vnode **vpp)
{
        struct vnode *vp;
        int error;

restart:
        if (mp->mnt_rootvnode != NULL) {
                MNT_ILOCK(mp);
                vp = mp->mnt_rootvnode;
                if (vp != NULL) {
                        if (!VN_IS_DOOMED(vp)) {
                                vrefact(vp);
                                MNT_IUNLOCK(mp);
                                error = vn_lock(vp, flags);
                                if (error == 0) {
                                        *vpp = vp;
                                        return (0);
                                }
                                vrele(vp);
                                goto restart;
                        }
                        /*
                         * Clear the old one.
                         */
                        mp->mnt_rootvnode = NULL;
                }
                MNT_IUNLOCK(mp);
                if (vp != NULL) {
                        /*
                         * Paired with a fence in vfs_op_thread_exit().
                         */
                        atomic_thread_fence_acq();
                        vfs_op_barrier_wait(mp);
                        vrele(vp);
                }
        }
        error = VFS_CACHEDROOT(mp, flags, vpp);
        if (error != 0)
                return (error);
        if (mp->mnt_vfs_ops == 0) {
                MNT_ILOCK(mp);
                if (mp->mnt_vfs_ops != 0) {
                        MNT_IUNLOCK(mp);
                        return (0);
                }
                if (mp->mnt_rootvnode == NULL) {
                        vrefact(*vpp);
                        mp->mnt_rootvnode = *vpp;
                } else {
                        if (mp->mnt_rootvnode != *vpp) {
                                if (!VN_IS_DOOMED(mp->mnt_rootvnode)) {
                                        panic("%s: mismatch between vnode returned "
                                            " by VFS_CACHEDROOT and the one cached "
                                            " (%p != %p)",
                                            __func__, *vpp, mp->mnt_rootvnode);
                                }
                        }
                }
                MNT_IUNLOCK(mp);
        }
        return (0);
}

int
vfs_cache_root(struct mount *mp, int flags, struct vnode **vpp)
{
        struct vnode *vp;
        int error;

        if (!vfs_op_thread_enter(mp))
                return (vfs_cache_root_fallback(mp, flags, vpp));
        vp = (struct vnode *)atomic_load_ptr(&mp->mnt_rootvnode);
        if (vp == NULL || VN_IS_DOOMED(vp)) {
                vfs_op_thread_exit(mp);
                return (vfs_cache_root_fallback(mp, flags, vpp));
        }
        vrefact(vp);
        vfs_op_thread_exit(mp);
        error = vn_lock(vp, flags);
        if (error != 0) {
                vrele(vp);
                return (vfs_cache_root_fallback(mp, flags, vpp));
        }
        *vpp = vp;
        return (0);
}

struct vnode *
vfs_cache_root_clear(struct mount *mp)
{
        struct vnode *vp;

        /*
         * ops > 0 guarantees there is nobody who can see this vnode
         */
        MPASS(mp->mnt_vfs_ops > 0);
        vp = mp->mnt_rootvnode;
        mp->mnt_rootvnode = NULL;
        return (vp);
}

void
vfs_cache_root_set(struct mount *mp, struct vnode *vp)
{

        MPASS(mp->mnt_vfs_ops > 0);
        vrefact(vp);
        mp->mnt_rootvnode = vp;
}

/*
 * These are helper functions for filesystems to traverse all
 * their vnodes.  See MNT_VNODE_FOREACH_ALL() in sys/mount.h.
 *
 * This interface replaces MNT_VNODE_FOREACH.
 */


struct vnode *
__mnt_vnode_next_all(struct vnode **mvp, struct mount *mp)
{
        struct vnode *vp;

        if (should_yield())
                kern_yield(PRI_USER);
        MNT_ILOCK(mp);
        KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
        for (vp = TAILQ_NEXT(*mvp, v_nmntvnodes); vp != NULL;
            vp = TAILQ_NEXT(vp, v_nmntvnodes)) {
                /* Allow a racy peek at VIRF_DOOMED to save a lock acquisition. */
                if (vp->v_type == VMARKER || VN_IS_DOOMED(vp))
                        continue;
                VI_LOCK(vp);
                if (VN_IS_DOOMED(vp)) {
                        VI_UNLOCK(vp);
                        continue;
                }
                break;
        }
        if (vp == NULL) {
                __mnt_vnode_markerfree_all(mvp, mp);
                /* MNT_IUNLOCK(mp); -- done in above function */
                mtx_assert(MNT_MTX(mp), MA_NOTOWNED);
                return (NULL);
        }
        TAILQ_REMOVE(&mp->mnt_nvnodelist, *mvp, v_nmntvnodes);
        TAILQ_INSERT_AFTER(&mp->mnt_nvnodelist, vp, *mvp, v_nmntvnodes);
        MNT_IUNLOCK(mp);
        return (vp);
}

struct vnode *
__mnt_vnode_first_all(struct vnode **mvp, struct mount *mp)
{
        struct vnode *vp;

        *mvp = vn_alloc_marker(mp);
        MNT_ILOCK(mp);
        MNT_REF(mp);

        TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                /* Allow a racy peek at VIRF_DOOMED to save a lock acquisition. */
                if (vp->v_type == VMARKER || VN_IS_DOOMED(vp))
                        continue;
                VI_LOCK(vp);
                if (VN_IS_DOOMED(vp)) {
                        VI_UNLOCK(vp);
                        continue;
                }
                break;
        }
        if (vp == NULL) {
                MNT_REL(mp);
                MNT_IUNLOCK(mp);
                vn_free_marker(*mvp);
                *mvp = NULL;
                return (NULL);
        }
        TAILQ_INSERT_AFTER(&mp->mnt_nvnodelist, vp, *mvp, v_nmntvnodes);
        MNT_IUNLOCK(mp);
        return (vp);
}

void
__mnt_vnode_markerfree_all(struct vnode **mvp, struct mount *mp)
{

        if (*mvp == NULL) {
                MNT_IUNLOCK(mp);
                return;
        }

        mtx_assert(MNT_MTX(mp), MA_OWNED);

        KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
        TAILQ_REMOVE(&mp->mnt_nvnodelist, *mvp, v_nmntvnodes);
        MNT_REL(mp);
        MNT_IUNLOCK(mp);
        vn_free_marker(*mvp);
        *mvp = NULL;
}

/*
 * These are helper functions for filesystems to traverse their
 * lazy vnodes.  See MNT_VNODE_FOREACH_LAZY() in sys/mount.h
 */
static void
mnt_vnode_markerfree_lazy(struct vnode **mvp, struct mount *mp)
{

        KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));

        MNT_ILOCK(mp);
        MNT_REL(mp);
        MNT_IUNLOCK(mp);
        vn_free_marker(*mvp);
        *mvp = NULL;
}

/*
 * Relock the mp mount vnode list lock with the vp vnode interlock in the
 * conventional lock order during mnt_vnode_next_lazy iteration.
 *
 * On entry, the mount vnode list lock is held and the vnode interlock is not.
 * The list lock is dropped and reacquired.  On success, both locks are held.
 * On failure, the mount vnode list lock is held but the vnode interlock is
 * not, and the procedure may have yielded.
 */
static bool
mnt_vnode_next_lazy_relock(struct vnode *mvp, struct mount *mp,
    struct vnode *vp)
{
        const struct vnode *tmp;
        bool held, ret;

        VNASSERT(mvp->v_mount == mp && mvp->v_type == VMARKER &&
            TAILQ_NEXT(mvp, v_lazylist) != NULL, mvp,
            ("%s: bad marker", __func__));
        VNASSERT(vp->v_mount == mp && vp->v_type != VMARKER, vp,
            ("%s: inappropriate vnode", __func__));
        ASSERT_VI_UNLOCKED(vp, __func__);
        mtx_assert(&mp->mnt_listmtx, MA_OWNED);

        ret = false;

        TAILQ_REMOVE(&mp->mnt_lazyvnodelist, mvp, v_lazylist);
        TAILQ_INSERT_BEFORE(vp, mvp, v_lazylist);

        /*
         * Use a hold to prevent vp from disappearing while the mount vnode
         * list lock is dropped and reacquired.  Normally a hold would be
         * acquired with vhold(), but that might try to acquire the vnode
         * interlock, which would be a LOR with the mount vnode list lock.
         */
        held = refcount_acquire_if_not_zero(&vp->v_holdcnt);
        mtx_unlock(&mp->mnt_listmtx);
        if (!held)
                goto abort;
        VI_LOCK(vp);
        if (!refcount_release_if_not_last(&vp->v_holdcnt)) {
                vdropl(vp);
                goto abort;
        }
        mtx_lock(&mp->mnt_listmtx);

        /*
         * Determine whether the vnode is still the next one after the marker,
         * excepting any other markers.  If the vnode has not been doomed by
         * vgone() then the hold should have ensured that it remained on the
         * lazy list.  If it has been doomed but is still on the lazy list,
         * don't abort, but rather skip over it (avoid spinning on doomed
         * vnodes).
         */
        tmp = mvp;
        do {
                tmp = TAILQ_NEXT(tmp, v_lazylist);
        } while (tmp != NULL && tmp->v_type == VMARKER);
        if (tmp != vp) {
                mtx_unlock(&mp->mnt_listmtx);
                VI_UNLOCK(vp);
                goto abort;
        }

        ret = true;
        goto out;
abort:
        maybe_yield();
        mtx_lock(&mp->mnt_listmtx);
out:
        if (ret)
                ASSERT_VI_LOCKED(vp, __func__);
        else
                ASSERT_VI_UNLOCKED(vp, __func__);
        mtx_assert(&mp->mnt_listmtx, MA_OWNED);
        return (ret);
}

static struct vnode *
mnt_vnode_next_lazy(struct vnode **mvp, struct mount *mp, mnt_lazy_cb_t *cb,
    void *cbarg)
{
        struct vnode *vp, *nvp;

        mtx_assert(&mp->mnt_listmtx, MA_OWNED);
        KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
restart:
        vp = TAILQ_NEXT(*mvp, v_lazylist);
        while (vp != NULL) {
                if (vp->v_type == VMARKER) {
                        vp = TAILQ_NEXT(vp, v_lazylist);
                        continue;
                }
                /*
                 * See if we want to process the vnode. Note we may encounter a
                 * long string of vnodes we don't care about and hog the list
                 * as a result. Check for it and requeue the marker.
                 */
                if (VN_IS_DOOMED(vp) || !cb(vp, cbarg)) {
                        if (!should_yield()) {
                                vp = TAILQ_NEXT(vp, v_lazylist);
                                continue;
                        }
                        TAILQ_REMOVE(&mp->mnt_lazyvnodelist, *mvp,
                            v_lazylist);
                        TAILQ_INSERT_AFTER(&mp->mnt_lazyvnodelist, vp, *mvp,
                            v_lazylist);
                        mtx_unlock(&mp->mnt_listmtx);
                        kern_yield(PRI_USER);
                        mtx_lock(&mp->mnt_listmtx);
                        goto restart;
                }
                /*
                 * Try-lock because this is the wrong lock order.  If that does
                 * not succeed, drop the mount vnode list lock and try to
                 * reacquire it and the vnode interlock in the right order.
                 */
                if (!VI_TRYLOCK(vp) &&
                    !mnt_vnode_next_lazy_relock(*mvp, mp, vp))
                        goto restart;
                KASSERT(vp->v_type != VMARKER, ("locked marker %p", vp));
                KASSERT(vp->v_mount == mp || vp->v_mount == NULL,
                    ("alien vnode on the lazy list %p %p", vp, mp));
                if (vp->v_mount == mp && !VN_IS_DOOMED(vp))
                        break;
                nvp = TAILQ_NEXT(vp, v_lazylist);
                VI_UNLOCK(vp);
                vp = nvp;
        }
        TAILQ_REMOVE(&mp->mnt_lazyvnodelist, *mvp, v_lazylist);

        /* Check if we are done */
        if (vp == NULL) {
                mtx_unlock(&mp->mnt_listmtx);
                mnt_vnode_markerfree_lazy(mvp, mp);
                return (NULL);
        }
        TAILQ_INSERT_AFTER(&mp->mnt_lazyvnodelist, vp, *mvp, v_lazylist);
        mtx_unlock(&mp->mnt_listmtx);
        ASSERT_VI_LOCKED(vp, "lazy iter");
        return (vp);
}

struct vnode *
__mnt_vnode_next_lazy(struct vnode **mvp, struct mount *mp, mnt_lazy_cb_t *cb,
    void *cbarg)
{

        if (should_yield())
                kern_yield(PRI_USER);
        mtx_lock(&mp->mnt_listmtx);
        return (mnt_vnode_next_lazy(mvp, mp, cb, cbarg));
}

struct vnode *
__mnt_vnode_first_lazy(struct vnode **mvp, struct mount *mp, mnt_lazy_cb_t *cb,
    void *cbarg)
{
        struct vnode *vp;

        *mvp = vn_alloc_marker(mp);
        MNT_ILOCK(mp);
        MNT_REF(mp);
        MNT_IUNLOCK(mp);

        mtx_lock(&mp->mnt_listmtx);
        vp = TAILQ_FIRST(&mp->mnt_lazyvnodelist);
        if (vp == NULL) {
                mtx_unlock(&mp->mnt_listmtx);
                mnt_vnode_markerfree_lazy(mvp, mp);
                return (NULL);
        }
        TAILQ_INSERT_BEFORE(vp, *mvp, v_lazylist);
        return (mnt_vnode_next_lazy(mvp, mp, cb, cbarg));
}

void
__mnt_vnode_markerfree_lazy(struct vnode **mvp, struct mount *mp)
{

        if (*mvp == NULL)
                return;

        mtx_lock(&mp->mnt_listmtx);
        TAILQ_REMOVE(&mp->mnt_lazyvnodelist, *mvp, v_lazylist);
        mtx_unlock(&mp->mnt_listmtx);
        mnt_vnode_markerfree_lazy(mvp, mp);
}