Holding a vnode doesn't prevent v_mount from disappearing (when the

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

/*-
 * 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.
 * 4. 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_mac.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/bio.h>
#include <sys/buf.h>
#include <sys/conf.h>
#include <sys/event.h>
#include <sys/eventhandler.h>
#include <sys/extattr.h>
#include <sys/file.h>
#include <sys/fcntl.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/mac.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/reboot.h>
#include <sys/sleepqueue.h>
#include <sys/stat.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>

#include <machine/stdarg.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>

static MALLOC_DEFINE(M_NETADDR, "Export Host", "Export host address structure");

static void     delmntque(struct vnode *vp);
static void     insmntque(struct vnode *vp, struct mount *mp);
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     vbusy(struct vnode *vp);
static void     vdropl(struct vnode *vp);
static void     vinactive(struct vnode *, struct thread *);
static void     v_incr_usecount(struct vnode *);
static void     v_decr_usecount(struct vnode *);
static void     v_decr_useonly(struct vnode *);
static void     vfree(struct vnode *);
static void     vnlru_free(int);
static void     vdestroy(struct vnode *);
static void     vgonel(struct vnode *);
static void     vfs_knllock(void *arg);
static void     vfs_knlunlock(void *arg);
static int      vfs_knllocked(void *arg);


/*
 * Enable Giant pushdown based on whether or not the vm is mpsafe in this
 * build.  Without mpsafevm the buffer cache can not run Giant free.
 */
#if defined(__alpha__) || defined(__amd64__) || defined(__i386__)
int mpsafe_vfs = 1;
#else
int mpsafe_vfs;
#endif
TUNABLE_INT("debug.mpsafevfs", &mpsafe_vfs);
SYSCTL_INT(_debug, OID_AUTO, mpsafevfs, CTLFLAG_RD, &mpsafe_vfs, 0,
    "MPSAFE VFS");

/*
 * Number of vnodes in existence.  Increased whenever getnewvnode()
 * allocates a new vnode, never decreased.
 */
static unsigned long    numvnodes;

SYSCTL_LONG(_vfs, OID_AUTO, numvnodes, CTLFLAG_RD, &numvnodes, 0, "");

/*
 * 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, VBAD,
};
int vttoif_tab[9] = {
        0, S_IFREG, S_IFDIR, S_IFBLK, S_IFCHR, S_IFLNK,
        S_IFSOCK, S_IFIFO, S_IFMT,
};

/*
 * List of vnodes that are ready for recycling.
 */
static TAILQ_HEAD(freelst, vnode) vnode_free_list;

/*
 * Free vnode target.  Free vnodes may simply be files which have been stat'd
 * but not read.  This is somewhat common, and a small cache of such files
 * should be kept to avoid recreation costs.
 */
static u_long wantfreevnodes;
SYSCTL_LONG(_vfs, OID_AUTO, wantfreevnodes, CTLFLAG_RW, &wantfreevnodes, 0, "");
/* Number of vnodes in the free list. */
static u_long freevnodes;
SYSCTL_LONG(_vfs, OID_AUTO, freevnodes, CTLFLAG_RD, &freevnodes, 0, "");

/*
 * 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, &reassignbufcalls, 0, "");

/*
 * Cache for the mount type id assigned to NFS.  This is used for
 * special checks in nfs/nfs_nqlease.c and vm/vnode_pager.c.
 */
int     nfs_mount_type = -1;

/* 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_free_list
 *      numvnodes
 *      freevnodes
 */
static struct mtx vnode_free_list_mtx;

/* Publicly exported FS */
struct nfs_public nfs_pub;

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

/* Set to 1 to print out reclaim of active vnodes */
int     prtactive;

/*
 * 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;

#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, "");
static int dirdelay = 29;               /* time to delay syncing directories */
SYSCTL_INT(_kern, OID_AUTO, dirdelay, CTLFLAG_RW, &dirdelay, 0, "");
static int metadelay = 28;              /* time to delay syncing metadata */
SYSCTL_INT(_kern, OID_AUTO, metadelay, CTLFLAG_RW, &metadelay, 0, "");
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, "");

/*
 * 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;

/*
 * Number of vnodes we want to exist at any one time.  This is mostly used
 * to size hash tables in vnode-related code.  It is normally not used in
 * getnewvnode(), as wantfreevnodes is normally nonzero.)
 *
 * XXX desiredvnodes is historical cruft and should not exist.
 */
int desiredvnodes;
SYSCTL_INT(_kern, KERN_MAXVNODES, maxvnodes, CTLFLAG_RW,
    &desiredvnodes, 0, "Maximum number of vnodes");
SYSCTL_INT(_kern, OID_AUTO, minvnodes, CTLFLAG_RW,
    &wantfreevnodes, 0, "Minimum number of vnodes (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");

/* Hook for calling soft updates. */
int (*softdep_process_worklist_hook)(struct mount *);

/*
 * Macros to control when a vnode is freed and recycled.  All require
 * the vnode interlock.
 */
#define VCANRECYCLE(vp) (((vp)->v_iflag & VI_FREE) && !(vp)->v_holdcnt)
#define VSHOULDFREE(vp) (!((vp)->v_iflag & VI_FREE) && !(vp)->v_holdcnt)
#define VSHOULDBUSY(vp) (((vp)->v_iflag & VI_FREE) && (vp)->v_holdcnt)


/*
 * Initialize the vnode management data structures.
 */
#ifndef MAXVNODES_MAX
#define MAXVNODES_MAX   100000
#endif
static void
vntblinit(void *dummy __unused)
{

        /*
         * Desiredvnodes is a function of the physical memory size and
         * the kernel's heap size.  Specifically, desiredvnodes scales
         * in proportion to the physical memory size until two fifths
         * of the kernel's heap size is consumed by vnodes and vm
         * objects.
         */
        desiredvnodes = min(maxproc + cnt.v_page_count / 4, 2 * vm_kmem_size /
            (5 * (sizeof(struct vm_object) + sizeof(struct vnode))));
        if (desiredvnodes > MAXVNODES_MAX) {
                if (bootverbose)
                        printf("Reducing kern.maxvnodes %d -> %d\n",
                            desiredvnodes, MAXVNODES_MAX);
                desiredvnodes = MAXVNODES_MAX;
        }
        wantfreevnodes = desiredvnodes / 4; 
        mtx_init(&mntid_mtx, "mntid", NULL, MTX_DEF);
        TAILQ_INIT(&vnode_free_list);
        mtx_init(&vnode_free_list_mtx, "vnode_free_list", NULL, MTX_DEF);
        vnode_zone = uma_zcreate("VNODE", sizeof (struct vnode), NULL, NULL,
            NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
        vnodepoll_zone = uma_zcreate("VNODEPOLL", sizeof (struct vpollinfo),
              NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
        /*
         * 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);
}
SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_FIRST, vntblinit, NULL)


/*
 * Mark a mount point as busy. Used to synchronize access and to delay
 * unmounting. Interlock is not released on failure.
 */
int
vfs_busy(mp, flags, interlkp, td)
        struct mount *mp;
        int flags;
        struct mtx *interlkp;
        struct thread *td;
{
        int lkflags;

        MNT_ILOCK(mp);
        if (mp->mnt_kern_flag & MNTK_UNMOUNT) {
                if (flags & LK_NOWAIT) {
                        MNT_IUNLOCK(mp);
                        return (ENOENT);
                }
                if (interlkp)
                        mtx_unlock(interlkp);
                mp->mnt_kern_flag |= MNTK_MWAIT;
                /*
                 * Since all busy locks are shared except the exclusive
                 * lock granted when unmounting, the only place that a
                 * wakeup needs to be done is at the release of the
                 * exclusive lock at the end of dounmount.
                 */
                msleep(mp, MNT_MTX(mp), PVFS|PDROP, "vfs_busy", 0);
                if (interlkp)
                        mtx_lock(interlkp);
                return (ENOENT);
        }
        if (interlkp)
                mtx_unlock(interlkp);
        lkflags = LK_SHARED | LK_INTERLOCK;
        if (lockmgr(&mp->mnt_lock, lkflags, MNT_MTX(mp), td))
                panic("vfs_busy: unexpected lock failure");
        return (0);
}

/*
 * Free a busy filesystem.
 */
void
vfs_unbusy(mp, td)
        struct mount *mp;
        struct thread *td;
{

        lockmgr(&mp->mnt_lock, LK_RELEASE, NULL, td);
}

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

        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]) {
                        mtx_unlock(&mountlist_mtx);
                        return (mp);
                }
        }
        mtx_unlock(&mountlist_mtx);
        return ((struct mount *) 0);
}

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

        if ((mp->mnt_flag & MNT_USER) == 0 ||
            mp->mnt_cred->cr_uid != td->td_ucred->cr_uid) {
                if ((error = suser(td)) != 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(mp)
        struct mount *mp;
{
        static u_int16_t mntid_base;
        fsid_t tfsid;
        int mtype;

        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 (vfs_getvfs(&tfsid) == NULL)
                        break;
        }
        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_SEC;
SYSCTL_INT(_vfs, OID_AUTO, timestamp_precision, CTLFLAG_RW,
    &timestamp_precision, 0, "");

/*
 * Get a current timestamp.
 */
void
vfs_timestamp(tsp)
        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(vap)
        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;
}

/*
 * 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
 * desireable 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.
 */
static int
vlrureclaim(struct mount *mp)
{
        struct thread *td;
        struct vnode *vp;
        int done;
        int trigger;
        int usevnodes;
        int count;

        /*
         * Calculate the trigger point, don't allow user
         * screwups to blow us up.   This prevents us from
         * recycling vnodes with lots of resident pages.  We
         * aren't trying to free memory, we are trying to
         * free vnodes.
         */
        usevnodes = desiredvnodes;
        if (usevnodes <= 0)
                usevnodes = 1;
        trigger = cnt.v_page_count * 2 / usevnodes;
        done = 0;
        td = curthread;
        vn_start_write(NULL, &mp, V_WAIT);
        MNT_ILOCK(mp);
        count = mp->mnt_nvnodelistsize / 10 + 1;
        while (count && (vp = TAILQ_FIRST(&mp->mnt_nvnodelist)) != NULL) {
                TAILQ_REMOVE(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
                TAILQ_INSERT_TAIL(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
                --count;
                if (!VI_TRYLOCK(vp))
                        continue;
                /*
                 * If it's been deconstructed already, it's still
                 * referenced, or it exceeds the trigger, skip it.
                 */
                if ((vp->v_iflag & VI_DOOMED) != 0 || vp->v_usecount ||
                    !LIST_EMPTY(&(vp)->v_cache_src) || (vp->v_object != NULL && 
                    vp->v_object->resident_page_count > trigger)) {
                        VI_UNLOCK(vp);
                        continue;
                }
                MNT_IUNLOCK(mp);
                vholdl(vp);
                if (VOP_LOCK(vp, LK_INTERLOCK|LK_EXCLUSIVE, td)) {
                        vdrop(vp);
                        MNT_ILOCK(mp);
                        continue;
                }
                VI_LOCK(vp);
                vgonel(vp);
                VOP_UNLOCK(vp, 0, td);
                vdropl(vp);
                done++;
                MNT_ILOCK(mp);
        }
        MNT_IUNLOCK(mp);
        vn_finished_write(mp);
        return done;
}

/*
 * Attempt to keep the free list at wantfreevnodes length.
 */
static void
vnlru_free(int count)
{
        struct vnode *vp;

        mtx_assert(&vnode_free_list_mtx, MA_OWNED);
        for (; count > 0; count--) {
                vp = TAILQ_FIRST(&vnode_free_list);
                /*
                 * The list can be modified while the free_list_mtx
                 * has been dropped and vp could be NULL here.
                 */
                if (!vp)
                        break;
                VNASSERT(vp->v_op != NULL, vp,
                    ("vnlru_free: vnode already reclaimed."));
                TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
                /*
                 * Don't recycle if we can't get the interlock.
                 */
                if (!VI_TRYLOCK(vp)) {
                        TAILQ_INSERT_TAIL(&vnode_free_list, vp, v_freelist);
                        continue;
                }
                VNASSERT(VCANRECYCLE(vp), vp,
                    ("vp inconsistent on freelist"));
                freevnodes--;
                vp->v_iflag &= ~VI_FREE;
                vholdl(vp);
                mtx_unlock(&vnode_free_list_mtx);
                VI_UNLOCK(vp);
                vtryrecycle(vp);
                /*
                 * If the recycled succeeded this vdrop will actually free
                 * the vnode.  If not it will simply place it back on
                 * the free list.
                 */
                vdrop(vp);
                mtx_lock(&vnode_free_list_mtx);
        }
}
/*
 * 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;

static void
vnlru_proc(void)
{
        struct mount *mp, *nmp;
        int done;
        struct proc *p = vnlruproc;
        struct thread *td = FIRST_THREAD_IN_PROC(p);

        mtx_lock(&Giant);

        EVENTHANDLER_REGISTER(shutdown_pre_sync, kproc_shutdown, p,
            SHUTDOWN_PRI_FIRST);

        for (;;) {
                kthread_suspend_check(p);
                mtx_lock(&vnode_free_list_mtx);
                if (freevnodes > wantfreevnodes)
                        vnlru_free(freevnodes - wantfreevnodes);
                if (numvnodes <= desiredvnodes * 9 / 10) {
                        vnlruproc_sig = 0;
                        wakeup(&vnlruproc_sig);
                        msleep(vnlruproc, &vnode_free_list_mtx,
                            PVFS|PDROP, "vlruwt", hz);
                        continue;
                }
                mtx_unlock(&vnode_free_list_mtx);
                done = 0;
                mtx_lock(&mountlist_mtx);
                for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
                        int vfsunlocked;
                        if (vfs_busy(mp, LK_NOWAIT, &mountlist_mtx, td)) {
                                nmp = TAILQ_NEXT(mp, mnt_list);
                                continue;
                        }
                        if (!VFS_NEEDSGIANT(mp)) {
                                mtx_unlock(&Giant);
                                vfsunlocked = 1;
                        } else
                                vfsunlocked = 0;
                        done += vlrureclaim(mp);
                        if (vfsunlocked)
                                mtx_lock(&Giant);
                        mtx_lock(&mountlist_mtx);
                        nmp = TAILQ_NEXT(mp, mnt_list);
                        vfs_unbusy(mp, td);
                }
                mtx_unlock(&mountlist_mtx);
                if (done == 0) {
#if 0
                        /* These messages are temporary debugging aids */
                        if (vnlru_nowhere < 5)
                                printf("vnlru process getting nowhere..\n");
                        else if (vnlru_nowhere == 5)
                                printf("vnlru process messages stopped.\n");
#endif
                        vnlru_nowhere++;
                        tsleep(vnlruproc, PPAUSE, "vlrup", hz * 3);
                } else 
                        uio_yield();
        }
}

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.
 */

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

        CTR1(KTR_VFS, "vdestroy vp %p", vp);
        mtx_lock(&vnode_free_list_mtx);
        numvnodes--;
        mtx_unlock(&vnode_free_list_mtx);
        bo = &vp->v_bufobj;
        VNASSERT((vp->v_iflag & VI_FREE) == 0, vp,
            ("cleaned vnode still on the free list."));
        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(bo->bo_clean.bv_root == NULL, vp, ("cleanblkroot not NULL"));
        VNASSERT(bo->bo_dirty.bv_cnt == 0, vp, ("dirtybufcnt not 0"));
        VNASSERT(bo->bo_dirty.bv_root == NULL, vp, ("dirtyblkroot not NULL"));
        VNASSERT(TAILQ_EMPTY(&vp->v_cache_dst), vp, ("vp has namecache dst"));
        VNASSERT(LIST_EMPTY(&vp->v_cache_src), vp, ("vp has namecache src"));
        VI_UNLOCK(vp);
#ifdef MAC
        mac_destroy_vnode(vp);
#endif
        if (vp->v_pollinfo != NULL) {
                knlist_destroy(&vp->v_pollinfo->vpi_selinfo.si_note);
                mtx_destroy(&vp->v_pollinfo->vpi_lock);
                uma_zfree(vnodepoll_zone, vp->v_pollinfo);
        }
#ifdef INVARIANTS
        /* XXX Elsewhere we can detect an already freed vnode via NULL v_op. */
        vp->v_op = NULL;
#endif
        lockdestroy(vp->v_vnlock);
        mtx_destroy(&vp->v_interlock);
        uma_zfree(vnode_zone, vp);
}

/*
 * 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 thread *td = curthread;
        struct mount *vnmp;

        CTR1(KTR_VFS, "vtryrecycle: trying vp %p", 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, td) != 0)
                return (EWOULDBLOCK);
        /*
         * Don't recycle if its filesystem is being suspended.
         */
        if (vn_start_write(vp, &vnmp, V_NOWAIT) != 0) {
                VOP_UNLOCK(vp, 0, td);
                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, LK_INTERLOCK, td);
                vn_finished_write(vnmp);
                return (EBUSY);
        }
        if ((vp->v_iflag & VI_DOOMED) == 0)
                vgonel(vp);
        VOP_UNLOCK(vp, LK_INTERLOCK, td);
        vn_finished_write(vnmp);
        CTR1(KTR_VFS, "vtryrecycle: recycled vp %p", vp);
        return (0);
}

/*
 * Return the next vnode from the free list.
 */
int
getnewvnode(tag, mp, vops, vpp)
        const char *tag;
        struct mount *mp;
        struct vop_vector *vops;
        struct vnode **vpp;
{
        struct vnode *vp = NULL;
        struct bufobj *bo;

        mtx_lock(&vnode_free_list_mtx);
        /*
         * Lend our context to reclaim vnodes if they've exceeded the max.
         */
        if (freevnodes > wantfreevnodes)
                vnlru_free(1);
        /*
         * Wait for available vnodes.
         */
        if (numvnodes > desiredvnodes) {
                if (vnlruproc_sig == 0) {
                        vnlruproc_sig = 1;      /* avoid unnecessary wakeups */
                        wakeup(vnlruproc);
                }
                msleep(&vnlruproc_sig, &vnode_free_list_mtx, PVFS,
                    "vlruwk", hz);
#if 0   /* XXX Not all VFS_VGET/ffs_vget callers check returns. */
                if (numvnodes > desiredvnodes) {
                        mtx_unlock(&vnode_free_list_mtx);
                        return (ENFILE);
                }
#endif
        }
        numvnodes++;
        mtx_unlock(&vnode_free_list_mtx);
        vp = (struct vnode *) uma_zalloc(vnode_zone, M_WAITOK|M_ZERO);
        /*
         * 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, tag, VLKTIMEOUT, LK_NOSHARE);
        /*
         * Initialize bufobj.
         */
        bo = &vp->v_bufobj;
        bo->__bo_vnode = vp;
        bo->bo_mtx = &vp->v_interlock;
        bo->bo_ops = &buf_ops_bio;
        bo->bo_private = vp;
        TAILQ_INIT(&bo->bo_clean.bv_hd);
        TAILQ_INIT(&bo->bo_dirty.bv_hd);
        /*
         * Initialize namecache.
         */
        LIST_INIT(&vp->v_cache_src);
        TAILQ_INIT(&vp->v_cache_dst);
        /*
         * Finalize various vnode identity bits.
         */
        vp->v_type = VNON;
        vp->v_tag = tag;
        vp->v_op = vops;
        v_incr_usecount(vp);
        vp->v_data = 0;
#ifdef MAC
        mac_init_vnode(vp);
        if (mp != NULL && (mp->mnt_flag & MNT_MULTILABEL) == 0)
                mac_associate_vnode_singlelabel(mp, vp);
        else if (mp == NULL)
                printf("NULL mp in getnewvnode()\n");
#endif
        delmntque(vp);
        if (mp != NULL) {
                insmntque(vp, mp);
                bo->bo_bsize = mp->mnt_stat.f_iosize;
                if ((mp->mnt_kern_flag & MNTK_NOKNOTE) != 0)
                        vp->v_vflag |= VV_NOKNOTE;
        }

        CTR2(KTR_VFS, "getnewvnode: mp %p vp %p", mp, vp);
        *vpp = vp;
        return (0);
}

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

        if (vp->v_mount == NULL)
                return;
        mp = vp->v_mount;
        MNT_ILOCK(mp);
        vp->v_mount = NULL;
        VNASSERT(mp->mnt_nvnodelistsize > 0, vp,
                ("bad mount point vnode list size"));
        TAILQ_REMOVE(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
        mp->mnt_nvnodelistsize--;
        MNT_IUNLOCK(mp);
}

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

        vp->v_mount = mp;
        VNASSERT(mp != NULL, vp, ("Don't call insmntque(foo, NULL)"));
        MNT_ILOCK(vp->v_mount);
        TAILQ_INSERT_TAIL(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
        mp->mnt_nvnodelistsize++;
        MNT_IUNLOCK(vp->v_mount);
}

/*
 * Flush out and invalidate all buffers associated with a bufobj
 * Called with the underlying object locked.
 */
int
bufobj_invalbuf(struct bufobj *bo, int flags, struct thread *td, 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, td)) != 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)
                        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);
                BO_UNLOCK(bo);
                if (bo->bo_object != NULL) {
                        VM_OBJECT_LOCK(bo->bo_object);
                        vm_object_pip_wait(bo->bo_object, "bovlbx");
                        VM_OBJECT_UNLOCK(bo->bo_object);
                }
                BO_LOCK(bo);
        } while (bo->bo_numoutput > 0);
        BO_UNLOCK(bo);

        /*
         * Destroy the copy in the VM cache, too.
         */
        if (bo->bo_object != NULL) {
                VM_OBJECT_LOCK(bo->bo_object);
                vm_object_page_remove(bo->bo_object, 0, 0,
                        (flags & V_SAVE) ? TRUE : FALSE);
                VM_OBJECT_UNLOCK(bo->bo_object);
        }

#ifdef INVARIANTS
        BO_LOCK(bo);
        if ((flags & (V_ALT | V_NORMAL)) == 0 &&
            (bo->bo_dirty.bv_cnt > 0 || bo->bo_clean.bv_cnt > 0))
                panic("vinvalbuf: flush 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, struct thread *td, int slpflag, int slptimeo)
{

        CTR2(KTR_VFS, "vinvalbuf vp %p flags %d", vp, flags);
        ASSERT_VOP_LOCKED(vp, "vinvalbuf");
        return (bufobj_invalbuf(&vp->v_bufobj, flags, td, slpflag, slptimeo));
}

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

        ASSERT_BO_LOCKED(bo);

        retval = 0;
        TAILQ_FOREACH_SAFE(bp, &bufv->bv_hd, b_bobufs, nbp) {
                if (((flags & V_NORMAL) && (bp->b_xflags & BX_ALTDATA)) ||
                    ((flags & V_ALT) && (bp->b_xflags & BX_ALTDATA) == 0)) {
                        continue;
                }
                retval = EAGAIN;
                error = BUF_TIMELOCK(bp,
                    LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK, BO_MTX(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));
                if (bp->b_bufobj != bo) {       /* XXX: necessary ? */
                        BUF_UNLOCK(bp);
                        BO_LOCK(bo);
                        return (EAGAIN);
                }
                /*
                 * 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_NOCACHE | B_RELBUF);
                bp->b_flags &= ~B_ASYNC;
                brelse(bp);
                BO_LOCK(bo);
        }
        return (retval);
}

/*
 * 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, struct ucred *cred, struct thread *td, off_t length, int blksize)
{
        struct buf *bp, *nbp;
        int anyfreed;
        int trunclbn;
        struct bufobj *bo;

        CTR2(KTR_VFS, "vtruncbuf vp %p length %jd", vp, length);
        /*
         * Round up to the *next* lbn.
         */
        trunclbn = (length + blksize - 1) / blksize;

        ASSERT_VOP_LOCKED(vp, "vtruncbuf");
restart:
        VI_LOCK(vp);
        bo = &vp->v_bufobj;
        anyfreed = 1;
        for (;anyfreed;) {
                anyfreed = 0;
                TAILQ_FOREACH_SAFE(bp, &bo->bo_clean.bv_hd, b_bobufs, nbp) {
                        if (bp->b_lblkno < trunclbn)
                                continue;
                        if (BUF_LOCK(bp,
                            LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                            VI_MTX(vp)) == ENOLCK)
                                goto restart;

                        bremfree(bp);
                        bp->b_flags |= (B_INVAL | B_RELBUF);
                        bp->b_flags &= ~B_ASYNC;
                        brelse(bp);
                        anyfreed = 1;

                        if (nbp != NULL &&
                            (((nbp->b_xflags & BX_VNCLEAN) == 0) ||
                            (nbp->b_vp != vp) ||
                            (nbp->b_flags & B_DELWRI))) {
                                goto restart;
                        }
                        VI_LOCK(vp);
                }

                TAILQ_FOREACH_SAFE(bp, &bo->bo_dirty.bv_hd, b_bobufs, nbp) {
                        if (bp->b_lblkno < trunclbn)
                                continue;
                        if (BUF_LOCK(bp,
                            LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                            VI_MTX(vp)) == ENOLCK)
                                goto restart;
                        bremfree(bp);
                        bp->b_flags |= (B_INVAL | B_RELBUF);
                        bp->b_flags &= ~B_ASYNC;
                        brelse(bp);
                        anyfreed = 1;
                        if (nbp != NULL &&
                            (((nbp->b_xflags & BX_VNDIRTY) == 0) ||
                            (nbp->b_vp != vp) ||
                            (nbp->b_flags & B_DELWRI) == 0)) {
                                goto restart;
                        }
                        VI_LOCK(vp);
                }
        }

        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,
                            VI_MTX(vp)) == ENOLCK) {
                                goto restart;
                        }
                        VNASSERT((bp->b_flags & B_DELWRI), vp,
                            ("buf(%p) on dirty queue without DELWRI", bp));

                        bremfree(bp);
                        bawrite(bp);
                        VI_LOCK(vp);
                        goto restartsync;
                }
        }

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

        return (0);
}

/*
 * buf_splay() - splay tree core for the clean/dirty list of buffers in
 *               a vnode.
 *
 *      NOTE: We have to deal with the special case of a background bitmap
 *      buffer, a situation where two buffers will have the same logical
 *      block offset.  We want (1) only the foreground buffer to be accessed
 *      in a lookup and (2) must differentiate between the foreground and
 *      background buffer in the splay tree algorithm because the splay
 *      tree cannot normally handle multiple entities with the same 'index'.
 *      We accomplish this by adding differentiating flags to the splay tree's
 *      numerical domain.
 */
static
struct buf *
buf_splay(daddr_t lblkno, b_xflags_t xflags, struct buf *root)
{
        struct buf dummy;
        struct buf *lefttreemax, *righttreemin, *y;

        if (root == NULL)
                return (NULL);
        lefttreemax = righttreemin = &dummy;
        for (;;) {
                if (lblkno < root->b_lblkno ||
                    (lblkno == root->b_lblkno &&
                    (xflags & BX_BKGRDMARKER) < (root->b_xflags & BX_BKGRDMARKER))) {
                        if ((y = root->b_left) == NULL)
                                break;
                        if (lblkno < y->b_lblkno) {
                                /* Rotate right. */
                                root->b_left = y->b_right;
                                y->b_right = root;
                                root = y;
                                if ((y = root->b_left) == NULL)
                                        break;
                        }
                        /* Link into the new root's right tree. */
                        righttreemin->b_left = root;
                        righttreemin = root;
                } else if (lblkno > root->b_lblkno ||
                    (lblkno == root->b_lblkno &&
                    (xflags & BX_BKGRDMARKER) > (root->b_xflags & BX_BKGRDMARKER))) {
                        if ((y = root->b_right) == NULL)
                                break;
                        if (lblkno > y->b_lblkno) {
                                /* Rotate left. */
                                root->b_right = y->b_left;
                                y->b_left = root;
                                root = y;
                                if ((y = root->b_right) == NULL)
                                        break;
                        }
                        /* Link into the new root's left tree. */
                        lefttreemax->b_right = root;
                        lefttreemax = root;
                } else {
                        break;
                }
                root = y;
        }
        /* Assemble the new root. */
        lefttreemax->b_right = root->b_left;
        righttreemin->b_left = root->b_right;
        root->b_left = dummy.b_right;
        root->b_right = dummy.b_left;
        return (root);
}

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

        KASSERT(bp->b_bufobj != NULL, ("No b_bufobj %p", bp));
        ASSERT_BO_LOCKED(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;
        if (bp != bv->bv_root) {
                root = buf_splay(bp->b_lblkno, bp->b_xflags, bv->bv_root);
                KASSERT(root == bp, ("splay lookup failed in remove"));
        }
        if (bp->b_left == NULL) {
                root = bp->b_right;
        } else {
                root = buf_splay(bp->b_lblkno, bp->b_xflags, bp->b_left);
                root->b_right = bp->b_right;
        }
        bv->bv_root = root;
        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 using a
 * splay tree algorithm.
 *
 * 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 buf *root;
        struct bufv *bv;

        ASSERT_BO_LOCKED(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;

        root = buf_splay(bp->b_lblkno, bp->b_xflags, bv->bv_root);
        if (root == NULL) {
                bp->b_left = NULL;
                bp->b_right = NULL;
                TAILQ_INSERT_TAIL(&bv->bv_hd, bp, b_bobufs);
        } else if (bp->b_lblkno < root->b_lblkno ||
            (bp->b_lblkno == root->b_lblkno &&
            (bp->b_xflags & BX_BKGRDMARKER) < (root->b_xflags & BX_BKGRDMARKER))) {
                bp->b_left = root->b_left;
                bp->b_right = root;
                root->b_left = NULL;
                TAILQ_INSERT_BEFORE(root, bp, b_bobufs);
        } else {
                bp->b_right = root->b_right;
                bp->b_left = root;
                root->b_right = NULL;
                TAILQ_INSERT_AFTER(&bv->bv_hd, root, bp, b_bobufs);
        }
        bv->bv_cnt++;
        bv->bv_root = bp;
}

/*
 * Lookup a buffer using the splay tree.  Note that we specifically avoid
 * shadow buffers used in background bitmap writes.
 *
 * This code isn't quite efficient as it could be because we are maintaining
 * two sorted lists and do not know which list the block resides in.
 *
 * During a "make buildworld" the desired buffer is found at one of
 * the roots more than 60% of the time.  Thus, checking both roots
 * before performing either splay eliminates unnecessary splays on the
 * first tree splayed.
 */
struct buf *
gbincore(struct bufobj *bo, daddr_t lblkno)
{
        struct buf *bp;

        ASSERT_BO_LOCKED(bo);
        if ((bp = bo->bo_clean.bv_root) != NULL &&
            bp->b_lblkno == lblkno && !(bp->b_xflags & BX_BKGRDMARKER))
                return (bp);
        if ((bp = bo->bo_dirty.bv_root) != NULL &&
            bp->b_lblkno == lblkno && !(bp->b_xflags & BX_BKGRDMARKER))
                return (bp);
        if ((bp = bo->bo_clean.bv_root) != NULL) {
                bo->bo_clean.bv_root = bp = buf_splay(lblkno, 0, bp);
                if (bp->b_lblkno == lblkno && !(bp->b_xflags & BX_BKGRDMARKER))
                        return (bp);
        }
        if ((bp = bo->bo_dirty.bv_root) != NULL) {
                bo->bo_dirty.bv_root = bp = buf_splay(lblkno, 0, bp);
                if (bp->b_lblkno == lblkno && !(bp->b_xflags & BX_BKGRDMARKER))
                        return (bp);
        }
        return (NULL);
}

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

        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));

        ASSERT_VI_LOCKED(vp, "bgetvp");
        vholdl(vp);
        bp->b_vp = vp;
        bp->b_bufobj = &vp->v_bufobj;
        /*
         * Insert onto list for new vnode.
         */
        buf_vlist_add(bp, &vp->v_bufobj, 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;
        vdropl(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_LOCKED(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_RD, NULL, 0,
    sysctl_vfs_worklist_len, "I", "Syncer thread worklist length");

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 bufobj *bo, struct thread *td)
{
        struct vnode *vp;
        struct mount *mp;

        vp = bo->__bo_vnode;    /* XXX */
        if (VOP_ISLOCKED(vp, NULL) != 0)
                return (1);
        if (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 (1);
        }
        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
        (void) VOP_FSYNC(vp, MNT_LAZY, td);
        VOP_UNLOCK(vp, 0, td);
        vn_finished_write(mp);
        VI_LOCK(vp);
        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);
        }
        vdropl(vp);
        mtx_lock(&sync_mtx);
        return (0);
}

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

        mtx_lock(&Giant);
        last_work_seen = 0;
        syncer_final_iter = 0;
        first_printf = 1;
        syncer_state = SYNCER_RUNNING;
        starttime = time_second;

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

        for (;;) {
                mtx_lock(&sync_mtx);
                if (syncer_state == SYNCER_FINAL_DELAY &&
                    syncer_final_iter == 0) {
                        mtx_unlock(&sync_mtx);
                        kthread_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_second) {
                        if (first_printf) {
                                printf("\nSyncing disks, vnodes remaining...");
                                first_printf = 0;
                        }
                        printf("%d ", net_worklist_len);
                }
                starttime = time_second;

                /*
                 * 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 ((bo = LIST_FIRST(slp)) != NULL) {
                        error = sync_vnode(bo, td);
                        if (error == 1) {
                                LIST_REMOVE(bo, bo_synclist);
                                LIST_INSERT_HEAD(next, bo, bo_synclist);
                                continue;
                        }
                }
                if (syncer_state == SYNCER_FINAL_DELAY && syncer_final_iter > 0)
                        syncer_final_iter--;
                mtx_unlock(&sync_mtx);

                /*
                 * Do soft update processing.
                 */
                if (softdep_process_worklist_hook != NULL)
                        (*softdep_process_worklist_hook)(NULL);

                /*
                 * 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.
                 */
                mtx_lock(&sync_mtx);
                if (rushjob > 0) {
                        rushjob -= 1;
                        mtx_unlock(&sync_mtx);
                        continue;
                }
                mtx_unlock(&sync_mtx);
                /*
                 * Just sleep for a short period if 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)
                        tsleep(&dummychan, PPAUSE, "syncfnl",
                            hz / SYNCER_SHUTDOWN_SPEEDUP);
                else if (time_second == starttime)
                        tsleep(&lbolt, PPAUSE, "syncer", 0);
        }
}

/*
 * 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()
{
        struct thread *td;
        int ret = 0;

        td = FIRST_THREAD_IN_PROC(updateproc);
        sleepq_remove(td, &lbolt);
        mtx_lock(&sync_mtx);
        if (rushjob < syncdelay / 2) {
                rushjob += 1;
                stat_rush_requests += 1;
                ret = 1;
        }
        mtx_unlock(&sync_mtx);
        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)
{
        struct thread *td;

        if (howto & RB_NOSYNC)
                return;
        td = FIRST_THREAD_IN_PROC(updateproc);
        sleepq_remove(td, &lbolt);
        mtx_lock(&sync_mtx);
        syncer_state = SYNCER_SHUTTING_DOWN;
        rushjob = 0;
        mtx_unlock(&sync_mtx);
        kproc_shutdown(arg, howto);
}

/*
 * 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.
         */
        VI_LOCK(vp);
        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
        VI_UNLOCK(vp);
}

/*
 * Increment the use and hold counts on the vnode, taking care to reference
 * the driver's usecount if this is a chardev.  The vholdl() will remove
 * the vnode from the free list if it is presently free.  Requires the
 * vnode interlock and returns with it held.
 */
static void
v_incr_usecount(struct vnode *vp)
{

        CTR3(KTR_VFS, "v_incr_usecount: vp %p holdcnt %d usecount %d\n",
            vp, vp->v_holdcnt, vp->v_usecount);
        vp->v_usecount++;
        if (vp->v_type == VCHR && vp->v_rdev != NULL) {
                dev_lock();
                vp->v_rdev->si_usecount++;
                dev_unlock();
        }
        vholdl(vp);
}

/*
 * Decrement the vnode use and hold count along with the driver's usecount
 * if this is a chardev.  The vdropl() below releases the vnode interlock
 * as it may free the vnode.
 */
static void
v_decr_usecount(struct vnode *vp)
{

        CTR3(KTR_VFS, "v_decr_usecount: vp %p holdcnt %d usecount %d\n",
            vp, vp->v_holdcnt, vp->v_usecount);
        ASSERT_VI_LOCKED(vp, __FUNCTION__);
        VNASSERT(vp->v_usecount > 0, vp,
            ("v_decr_usecount: negative usecount"));
        vp->v_usecount--;
        if (vp->v_type == VCHR && vp->v_rdev != NULL) {
                dev_lock();
                vp->v_rdev->si_usecount--;
                dev_unlock();
        }
        vdropl(vp);
}

/*
 * Decrement only the use count and driver use count.  This is intended to
 * be paired with a follow on vdropl() to release the remaining hold count.
 * In this way we may vgone() a vnode with a 0 usecount without risk of
 * having it end up on a free list because the hold count is kept above 0.
 */
static void
v_decr_useonly(struct vnode *vp)
{

        CTR3(KTR_VFS, "v_decr_useonly: vp %p holdcnt %d usecount %d\n",
            vp, vp->v_holdcnt, vp->v_usecount);
        ASSERT_VI_LOCKED(vp, __FUNCTION__);
        VNASSERT(vp->v_usecount > 0, vp,
            ("v_decr_useonly: negative usecount"));
        vp->v_usecount--;
        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. The vnode lock bit is set if the
 * vnode is being eliminated in vgone. The process is awakened
 * when the transition is completed, and an error returned to
 * indicate that the vnode is no longer usable (possibly having
 * been changed to a new filesystem type).
 */
int
vget(vp, flags, td)
        struct vnode *vp;
        int flags;
        struct thread *td;
{
        int oweinact;
        int oldflags;
        int error;

        error = 0;
        oldflags = flags;
        oweinact = 0;
        if ((flags & LK_INTERLOCK) == 0)
                VI_LOCK(vp);
        /*
         * If the inactive call was deferred because vput() was called
         * with a shared lock, we have to do it here before another thread
         * gets a reference to data that should be dead.
         */
        if (vp->v_iflag & VI_OWEINACT) {
                if (flags & LK_NOWAIT) {
                        VI_UNLOCK(vp);
                        return (EBUSY);
                }
                flags &= ~LK_TYPE_MASK;
                flags |= LK_EXCLUSIVE;
                oweinact = 1;
        }
        v_incr_usecount(vp);
        if ((error = vn_lock(vp, flags | LK_INTERLOCK, td)) != 0) {
                VI_LOCK(vp);
                /*
                 * must expand vrele here because we do not want
                 * to call VOP_INACTIVE if the reference count
                 * drops back to zero since it was never really
                 * active.
                 */
                v_decr_usecount(vp);
                return (error);
        }
        if (vp->v_iflag & VI_DOOMED && (flags & LK_RETRY) == 0)
                panic("vget: vn_lock failed to return ENOENT\n");
        if (oweinact) {
                VI_LOCK(vp);
                if (vp->v_iflag & VI_OWEINACT)
                        vinactive(vp, td);
                VI_UNLOCK(vp);
                if ((oldflags & LK_TYPE_MASK) == 0)
                        VOP_UNLOCK(vp, 0, td);
        }
        return (0);
}

/*
 * Increase the reference count of a vnode.
 */
void
vref(struct vnode *vp)
{

        VI_LOCK(vp);
        v_incr_usecount(vp);
        VI_UNLOCK(vp);
}

/*
 * Return reference count of a vnode.
 *
 * The results of this call are only guaranteed when some mechanism other
 * than the VI lock 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)
{
        int usecnt;

        VI_LOCK(vp);
        usecnt = vp->v_usecount;
        VI_UNLOCK(vp);

        return (usecnt);
}


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

        KASSERT(vp != NULL, ("vrele: null vp"));

        VI_LOCK(vp);

        /* Skip this v_writecount check if we're going to panic below. */
        VNASSERT(vp->v_writecount < vp->v_usecount || vp->v_usecount < 1, vp,
            ("vrele: missed vn_close"));

        if (vp->v_usecount > 1 || ((vp->v_iflag & VI_DOINGINACT) &&
            vp->v_usecount == 1)) {
                v_decr_usecount(vp);
                return;
        }
        if (vp->v_usecount != 1) {
#ifdef DIAGNOSTIC
                vprint("vrele: negative ref count", vp);
#endif
                VI_UNLOCK(vp);
                panic("vrele: negative ref cnt");
        }
        /*
         * 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.
         */
        v_decr_useonly(vp);
        /*
         * We must call VOP_INACTIVE with the node locked. Mark
         * as VI_DOINGINACT to avoid recursion.
         */
        if (vn_lock(vp, LK_EXCLUSIVE | LK_INTERLOCK, td) == 0) {
                VI_LOCK(vp);
                vinactive(vp, td);
                VOP_UNLOCK(vp, 0, td);
        } else
                VI_LOCK(vp);
        vdropl(vp);
}

/*
 * 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() aquires the lock internally.)
 */
void
vput(vp)
        struct vnode *vp;
{
        struct thread *td = curthread;  /* XXX */
        int error;

        KASSERT(vp != NULL, ("vput: null vp"));
        ASSERT_VOP_LOCKED(vp, "vput");
        VI_LOCK(vp);
        /* Skip this v_writecount check if we're going to panic below. */
        VNASSERT(vp->v_writecount < vp->v_usecount || vp->v_usecount < 1, vp,
            ("vput: missed vn_close"));
        error = 0;

        if (vp->v_usecount > 1 || ((vp->v_iflag & VI_DOINGINACT) &&
            vp->v_usecount == 1)) {
                VOP_UNLOCK(vp, 0, td);
                v_decr_usecount(vp);
                return;
        }

        if (vp->v_usecount != 1) {
#ifdef DIAGNOSTIC
                vprint("vput: negative ref count", vp);
#endif
                panic("vput: negative ref cnt");
        }
        /*
         * 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.
         */
        v_decr_useonly(vp);
        vp->v_iflag |= VI_OWEINACT;
        if (VOP_ISLOCKED(vp, NULL) != LK_EXCLUSIVE) {
                error = VOP_LOCK(vp, LK_EXCLUPGRADE|LK_INTERLOCK|LK_NOWAIT, td);
                VI_LOCK(vp);
                if (error)
                        goto done;
        }
        if (vp->v_iflag & VI_OWEINACT)
                vinactive(vp, td);
        VOP_UNLOCK(vp, 0, td);
done:
        vdropl(vp);
}

/*
 * Somebody doesn't want the vnode recycled.
 */
void
vhold(struct vnode *vp)
{

        VI_LOCK(vp);
        vholdl(vp);
        VI_UNLOCK(vp);
}

void
vholdl(struct vnode *vp)
{

        vp->v_holdcnt++;
        if (VSHOULDBUSY(vp))
                vbusy(vp);
}

/*
 * Note that there is one less who cares about this vnode.  vdrop() is the
 * opposite of vhold().
 */
void
vdrop(struct vnode *vp)
{

        VI_LOCK(vp);
        vdropl(vp);
}

/*
 * Drop the hold count of the vnode.  If this is the last reference to
 * the vnode we will free it if it has been vgone'd otherwise it is
 * placed on the free list.
 */
static void
vdropl(struct vnode *vp)
{

        if (vp->v_holdcnt <= 0)
                panic("vdrop: holdcnt %d", vp->v_holdcnt);
        vp->v_holdcnt--;
        if (vp->v_holdcnt == 0) {
                if (vp->v_iflag & VI_DOOMED) {
                        vdestroy(vp);
                        return;
                } else
                        vfree(vp);
        }
        VI_UNLOCK(vp);
}

/*
 * Call VOP_INACTIVE on the vnode and manage the DOINGINACT and OWEINACT
 * flags.  DOINGINACT prevents us from recursing in calls to vinactive.
 * OWEINACT tracks whether a vnode missed a call to inactive due to a
 * failed lock upgrade.
 */
static void
vinactive(struct vnode *vp, struct thread *td)
{

        ASSERT_VOP_LOCKED(vp, "vinactive");
        ASSERT_VI_LOCKED(vp, "vinactive");
        VNASSERT((vp->v_iflag & VI_DOINGINACT) == 0, vp,
            ("vinactive: recursed on VI_DOINGINACT"));
        vp->v_iflag |= VI_DOINGINACT;
        vp->v_iflag &= ~VI_OWEINACT;
        VI_UNLOCK(vp);
        VOP_INACTIVE(vp, td);
        VI_LOCK(vp);
        VNASSERT(vp->v_iflag & VI_DOINGINACT, vp,
            ("vinactive: lost VI_DOINGINACT"));
        vp->v_iflag &= ~VI_DOINGINACT;
}

/*
 * 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, "");
#endif

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

        CTR1(KTR_VFS, "vflush: mp %p", mp);
        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, td)) != 0)
                        return (error);
                vput(rootvp);

        }
        MNT_ILOCK(mp);
loop:
        MNT_VNODE_FOREACH(vp, mp, nvp) {

                VI_LOCK(vp);
                vholdl(vp);
                MNT_IUNLOCK(mp);
                error = vn_lock(vp, LK_INTERLOCK | LK_EXCLUSIVE, td);
                if (error) {
                        vdrop(vp);
                        MNT_ILOCK(mp);
                        goto loop;
                }
                /*
                 * Skip over a vnodes marked VV_SYSTEM.
                 */
                if ((flags & SKIPSYSTEM) && (vp->v_vflag & VV_SYSTEM)) {
                        VOP_UNLOCK(vp, 0, td);
                        vdrop(vp);
                        MNT_ILOCK(mp);
                        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) {
                        error = VOP_GETATTR(vp, &vattr, td->td_ucred, td);
                        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, 0, td);
                                vdropl(vp);
                                MNT_ILOCK(mp);
                                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)) {
                        VNASSERT(vp->v_usecount == 0 ||
                            (vp->v_type != VCHR && vp->v_type != VBLK), vp,
                            ("device VNODE %p is FORCECLOSED", vp));
                        vgonel(vp);
                } else {
                        busy++;
#ifdef DIAGNOSTIC
                        if (busyprt)
                                vprint("vflush: busy vnode", vp);
#endif
                }
                VOP_UNLOCK(vp, 0, td);
                vdropl(vp);
                MNT_ILOCK(mp);
        }
        MNT_IUNLOCK(mp);
        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, td);
                        vgone(rootvp);
                        VOP_UNLOCK(rootvp, 0, td);
                        busy = 0;
                } else
                        VI_UNLOCK(rootvp);
        }
        if (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, struct thread *td)
{
        int recycled;

        ASSERT_VOP_LOCKED(vp, "vrecycle");
        recycled = 0;
        VI_LOCK(vp);
        if (vp->v_usecount == 0) {
                recycled = 1;
                vgonel(vp);
        }
        VI_UNLOCK(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);
}

/*
 * vgone, with the vp interlock held.
 */
void
vgonel(struct vnode *vp)
{
        struct thread *td;
        int oweinact;
        int active;

        CTR1(KTR_VFS, "vgonel: vp %p", vp);
        ASSERT_VOP_LOCKED(vp, "vgonel");
        ASSERT_VI_LOCKED(vp, "vgonel");
#if 0
        /* XXX Need to fix ttyvp before I enable this. */
        VNASSERT(vp->v_holdcnt, vp,
            ("vgonel: vp %p has no reference.", vp));
#endif
        td = curthread;

        /*
         * Don't vgonel if we're already doomed.
         */
        if (vp->v_iflag & VI_DOOMED) {
                VI_UNLOCK(vp);
                return;
        }
        vp->v_iflag |= VI_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;
        oweinact = (vp->v_iflag & VI_OWEINACT);
        VI_UNLOCK(vp);
        /*
         * Clean out any buffers associated with the vnode.
         * If the flush fails, just toss the buffers.
         */
        if (!TAILQ_EMPTY(&vp->v_bufobj.bo_dirty.bv_hd))
                (void) vn_write_suspend_wait(vp, NULL, V_WAIT);
        if (vinvalbuf(vp, V_SAVE, td, 0, 0) != 0)
                vinvalbuf(vp, 0, td, 0, 0);

        /*
         * 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);
                if ((vp->v_iflag & VI_DOINGINACT) == 0)
                        vinactive(vp, td);
                VI_UNLOCK(vp);
        }
        /*
         * Reclaim the vnode.
         */
        if (VOP_RECLAIM(vp, td))
                panic("vgone: cannot reclaim");
        VNASSERT(vp->v_object == NULL, vp,
            ("vop_reclaim left v_object vp=%p, tag=%s", vp, vp->v_tag));
        /*
         * 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_tag = "none";
        vp->v_type = VBAD;
}

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

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

/*
 * Same as above, but using the struct cdev *as argument
 */
int
count_dev(dev)
        struct cdev *dev;
{
        int count;

        dev_lock();
        count = dev->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"};

void
vn_printf(struct vnode *vp, const char *fmt, ...)
{
        va_list ap;
        char buf[96];

        va_start(ap, fmt);
        vprintf(fmt, ap);
        va_end(ap);
        printf("%p: ", (void *)vp);
        printf("tag %s, type %s\n", vp->v_tag, typename[vp->v_type]);
        printf("    usecount %d, writecount %d, refcount %d mountedhere %p\n",
            vp->v_usecount, vp->v_writecount, vp->v_holdcnt, vp->v_mountedhere);
        buf[0] = '\0';
        buf[1] = '\0';
        if (vp->v_vflag & VV_ROOT)
                strcat(buf, "|VV_ROOT");
        if (vp->v_vflag & VV_TEXT)
                strcat(buf, "|VV_TEXT");
        if (vp->v_vflag & VV_SYSTEM)
                strcat(buf, "|VV_SYSTEM");
        if (vp->v_iflag & VI_DOOMED)
                strcat(buf, "|VI_DOOMED");
        if (vp->v_iflag & VI_FREE)
                strcat(buf, "|VI_FREE");
        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\n",
                    vp->v_object, vp->v_object->ref_count,
                    vp->v_object->resident_page_count);
        printf("    ");
        lockmgr_printinfo(vp->v_vnlock);
        printf("\n");
        if (vp->v_data != NULL)
                VOP_PRINT(vp);
}

#ifdef DDB
#include <ddb/ddb.h>
/*
 * List all of the locked vnodes in the system.
 * Called when debugging the kernel.
 */
DB_SHOW_COMMAND(lockedvnods, lockedvnodes)
{
        struct mount *mp, *nmp;
        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.
         */
        printf("Locked vnodes\n");
        for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
                nmp = TAILQ_NEXT(mp, mnt_list);
                TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                        if (VOP_ISLOCKED(vp, NULL))
                                vprint("", vp);
                }
                nmp = TAILQ_NEXT(mp, mnt_list);
        }
}
#endif

/*
 * Fill in a struct xvfsconf based on a struct vfsconf.
 */
static void
vfsconf2x(struct vfsconf *vfsp, struct xvfsconf *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;
}

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

        error = 0;
        TAILQ_FOREACH(vfsp, &vfsconf, vfc_list) {
                bzero(&xvfsp, sizeof(xvfsp));
                vfsconf2x(vfsp, &xvfsp);
                error = SYSCTL_OUT(req, &xvfsp, sizeof xvfsp);
                if (error)
                        break;
        }
        return (error);
}

SYSCTL_PROC(_vfs, OID_AUTO, conflist, CTLFLAG_RD, 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;
        struct xvfsconf xvfsp;

        printf("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 */
                TAILQ_FOREACH(vfsp, &vfsconf, vfc_list)
                        if (vfsp->vfc_typenum == name[2])
                                break;
                if (vfsp == NULL)
                        return (EOPNOTSUPP);
                bzero(&xvfsp, sizeof(xvfsp));
                vfsconf2x(vfsp, &xvfsp);
                return (SYSCTL_OUT(req, &xvfsp, sizeof(xvfsp)));
        }
        return (EOPNOTSUPP);
}

static SYSCTL_NODE(_vfs, VFS_GENERIC, generic, CTLFLAG_RD | CTLFLAG_SKIP,
        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;

        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)
                        return error;
        }
        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 thread *td = req->td;
        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, LK_NOWAIT, &mountlist_mtx, td))
                        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, td);
                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,
        0, 0, sysctl_vnode, "S,xvnode", "");
#endif

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

        KASSERT(curthread != NULL, ("vfs_unmountall: NULL curthread"));
        td = curthread;
        /*
         * Since this only runs when rebooting, it is not interlocked.
         */
        while(!TAILQ_EMPTY(&mountlist)) {
                mp = TAILQ_LAST(&mountlist, mntlist);
                error = dounmount(mp, MNT_FORCE, td);
                if (error) {
                        TAILQ_REMOVE(&mountlist, mp, mnt_list);
                        printf("unmount of %s failed (",
                            mp->mnt_stat.f_mntonname);
                        if (error == EBUSY)
                                printf("BUSY)\n");
                        else
                                printf("%d)\n", error);
                } else {
                        /* The unmount has removed mp from the mountlist */
                }
        }
}

/*
 * perform msync on all vnodes under a mount point
 * the mount point must be locked.
 */
void
vfs_msync(struct mount *mp, int flags)
{
        struct vnode *vp, *nvp;
        struct vm_object *obj;
        int tries;

        tries = 5;
        MNT_ILOCK(mp);
loop:
        TAILQ_FOREACH_SAFE(vp, &mp->mnt_nvnodelist, v_nmntvnodes, nvp) {
                if (vp->v_mount != mp) {
                        if (--tries > 0)
                                goto loop;
                        break;
                }

                VI_LOCK(vp);
                if ((vp->v_iflag & VI_OBJDIRTY) &&
                    (flags == MNT_WAIT || VOP_ISLOCKED(vp, NULL) == 0)) {
                        MNT_IUNLOCK(mp);
                        if (!vget(vp,
                            LK_EXCLUSIVE | LK_RETRY | LK_INTERLOCK,
                            curthread)) {
                                if (vp->v_vflag & VV_NOSYNC) {  /* unlinked */
                                        vput(vp);
                                        MNT_ILOCK(mp);
                                        continue;
                                }

                                obj = vp->v_object;
                                if (obj != NULL) {
                                        VM_OBJECT_LOCK(obj);
                                        vm_object_page_clean(obj, 0, 0,
                                            flags == MNT_WAIT ?
                                            OBJPC_SYNC : OBJPC_NOSYNC);
                                        VM_OBJECT_UNLOCK(obj);
                                }
                                vput(vp);
                        }
                        MNT_ILOCK(mp);
                        if (TAILQ_NEXT(vp, v_nmntvnodes) != nvp) {
                                if (--tries > 0)
                                        goto loop;
                                break;
                        }
                } else
                        VI_UNLOCK(vp);
        }
        MNT_IUNLOCK(mp);
}

/*
 * Mark a vnode as free, putting it up for recycling.
 */
static void
vfree(struct vnode *vp)
{

        CTR1(KTR_VFS, "vfree vp %p", vp);
        ASSERT_VI_LOCKED(vp, "vfree");
        mtx_lock(&vnode_free_list_mtx);
        VNASSERT(vp->v_op != NULL, vp, ("vfree: vnode already reclaimed."));
        VNASSERT((vp->v_iflag & VI_FREE) == 0, vp, ("vnode already free"));
        VNASSERT(VSHOULDFREE(vp), vp, ("vfree: freeing when we shouldn't"));
        VNASSERT((vp->v_iflag & VI_DOOMED) == 0, vp,
            ("vfree: Freeing doomed vnode"));
        if (vp->v_iflag & VI_AGE) {
                TAILQ_INSERT_HEAD(&vnode_free_list, vp, v_freelist);
        } else {
                TAILQ_INSERT_TAIL(&vnode_free_list, vp, v_freelist);
        }
        freevnodes++;
        vp->v_iflag &= ~VI_AGE;
        vp->v_iflag |= VI_FREE;
        mtx_unlock(&vnode_free_list_mtx);
}

/*
 * Opposite of vfree() - mark a vnode as in use.
 */
static void
vbusy(struct vnode *vp)
{
        CTR1(KTR_VFS, "vbusy vp %p", vp);
        ASSERT_VI_LOCKED(vp, "vbusy");
        VNASSERT((vp->v_iflag & VI_FREE) != 0, vp, ("vnode not free"));
        VNASSERT(vp->v_op != NULL, vp, ("vbusy: vnode already reclaimed."));

        mtx_lock(&vnode_free_list_mtx);
        TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
        freevnodes--;
        vp->v_iflag &= ~(VI_FREE|VI_AGE);
        mtx_unlock(&vnode_free_list_mtx);
}

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

        vi = uma_zalloc(vnodepoll_zone, M_WAITOK);
        if (vp->v_pollinfo != NULL) {
                uma_zfree(vnodepoll_zone, vi);
                return;
        }
        vp->v_pollinfo = vi;
        mtx_init(&vp->v_pollinfo->vpi_lock, "vnode pollinfo", NULL, MTX_DEF);
        knlist_init(&vp->v_pollinfo->vpi_selinfo.si_note, vp, vfs_knllock,
            vfs_knlunlock, vfs_knllocked);
}

/*
 * 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(vp, td, events)
        struct vnode *vp;
        struct thread *td;
        short events;
{

        if (vp->v_pollinfo == NULL)
                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_reclaim =  sync_reclaim,   /* reclaim */
        .vop_lock =     vop_stdlock,    /* lock */
        .vop_unlock =   vop_stdunlock,  /* unlock */
        .vop_islocked = vop_stdislocked,        /* islocked */
};

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

        /* Allocate a new vnode */
        if ((error = getnewvnode("syncer", mp, &sync_vnodeops, &vp)) != 0) {
                mp->mnt_syncer = NULL;
                return (error);
        }
        vp->v_type = VNON;
        /*
         * 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;
        }
        VI_LOCK(vp);
        vn_syncer_add_to_worklist(&vp->v_bufobj,
            syncdelay > 0 ? next % syncdelay : 0);
        /* XXX - vn_syncer_add_to_worklist() also grabs and drops sync_mtx. */
        mtx_lock(&sync_mtx);
        sync_vnode_count++;
        mtx_unlock(&sync_mtx);
        VI_UNLOCK(vp);
        mp->mnt_syncer = vp;
        return (0);
}

/*
 * Do a lazy sync of the filesystem.
 */
static int
sync_fsync(ap)
        struct vop_fsync_args /* {
                struct vnode *a_vp;
                struct ucred *a_cred;
                int a_waitfor;
                struct thread *a_td;
        } */ *ap;
{
        struct vnode *syncvp = ap->a_vp;
        struct mount *mp = syncvp->v_mount;
        struct thread *td = ap->a_td;
        int error, asyncflag;
        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.
         */
        mtx_lock(&mountlist_mtx);
        if (vfs_busy(mp, LK_EXCLUSIVE | LK_NOWAIT, &mountlist_mtx, td) != 0) {
                mtx_unlock(&mountlist_mtx);
                return (0);
        }
        if (vn_start_write(NULL, &mp, V_NOWAIT) != 0) {
                vfs_unbusy(mp, td);
                return (0);
        }
        asyncflag = mp->mnt_flag & MNT_ASYNC;
        mp->mnt_flag &= ~MNT_ASYNC;
        vfs_msync(mp, MNT_NOWAIT);
        error = VFS_SYNC(mp, MNT_LAZY, td);
        if (asyncflag)
                mp->mnt_flag |= MNT_ASYNC;
        vn_finished_write(mp);
        vfs_unbusy(mp, td);
        return (error);
}

/*
 * The syncer vnode is no referenced.
 */
static int
sync_inactive(ap)
        struct vop_inactive_args /* {
                struct vnode *a_vp;
                struct thread *a_td;
        } */ *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(ap)
        struct vop_reclaim_args /* {
                struct vnode *a_vp;
        } */ *ap;
{
        struct vnode *vp = ap->a_vp;
        struct bufobj *bo;

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

        return (0);
}

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

        error = 0;
        dev_lock();
        if (vp->v_type != VCHR)
                error = ENOTBLK;
        else 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();
        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(type, file_mode, file_uid, file_gid, acc_mode, cred, privused)
        enum vtype type;
        mode_t file_mode;
        uid_t file_uid;
        gid_t file_gid;
        mode_t acc_mode;
        struct ucred *cred;
        int *privused;
{
        mode_t dac_granted;
#ifdef CAPABILITIES
        mode_t cap_granted;
#endif

        /*
         * 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 ((acc_mode & dac_granted) == acc_mode)
                        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 ((acc_mode & dac_granted) == acc_mode)
                        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 ((acc_mode & dac_granted) == acc_mode)
                return (0);

privcheck:
        if (!suser_cred(cred, SUSER_ALLOWJAIL)) {
                /* XXX audit: privilege used */
                if (privused != NULL)
                        *privused = 1;
                return (0);
        }

#ifdef CAPABILITIES
        /*
         * Build a capability mask to determine if the set of capabilities
         * satisfies the requirements when combined with the granted mask
         * from above.
         * For each capability, if the capability is required, bitwise
         * or the request type onto the cap_granted mask.
         */
        cap_granted = 0;

        if (type == VDIR) {
                /*
                 * For directories, use CAP_DAC_READ_SEARCH to satisfy
                 * VEXEC requests, instead of CAP_DAC_EXECUTE.
                 */
                if ((acc_mode & VEXEC) && ((dac_granted & VEXEC) == 0) &&
                    !cap_check(cred, NULL, CAP_DAC_READ_SEARCH, SUSER_ALLOWJAIL))
                        cap_granted |= VEXEC;
        } else {
                if ((acc_mode & VEXEC) && ((dac_granted & VEXEC) == 0) &&
                    !cap_check(cred, NULL, CAP_DAC_EXECUTE, SUSER_ALLOWJAIL))
                        cap_granted |= VEXEC;
        }

        if ((acc_mode & VREAD) && ((dac_granted & VREAD) == 0) &&
            !cap_check(cred, NULL, CAP_DAC_READ_SEARCH, SUSER_ALLOWJAIL))
                cap_granted |= VREAD;

        if ((acc_mode & VWRITE) && ((dac_granted & VWRITE) == 0) &&
            !cap_check(cred, NULL, CAP_DAC_WRITE, SUSER_ALLOWJAIL))
                cap_granted |= (VWRITE | VAPPEND);

        if ((acc_mode & VADMIN) && ((dac_granted & VADMIN) == 0) &&
            !cap_check(cred, NULL, CAP_FOWNER, SUSER_ALLOWJAIL))
                cap_granted |= VADMIN;

        if ((acc_mode & (cap_granted | dac_granted)) == acc_mode) {
                /* XXX audit: privilege used */
                if (privused != NULL)
                        *privused = 1;
                return (0);
        }
#endif

        return ((acc_mode & 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, int access)
{

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

        /*
         * Do not allow privileged processes in jail to directly
         * manipulate system attributes.
         *
         * XXX What capability should apply here?
         * Probably CAP_SYS_SETFFLAG.
         */
        switch (attrnamespace) {
        case EXTATTR_NAMESPACE_SYSTEM:
                /* Potentially should be: return (EPERM); */
                return (suser_cred(cred, 0));
        case EXTATTR_NAMESPACE_USER:
                return (VOP_ACCESS(vp, access, cred, td));
        default:
                return (EPERM);
        }
}

#ifdef DEBUG_VFS_LOCKS
/*
 * This only exists to supress warnings from unlocked specfs accesses.  It is
 * no longer ok to have an unlocked VFS.
 */
#define IGNORE_LOCK(vp) ((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, "");

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

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

#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, "");
#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_print)
                printf("%s: %p %s\n", str, (void *)vp, msg);
        if (vfs_badlock_ddb)
                kdb_enter("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)
{

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

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

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

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

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

#if 0
void
assert_vop_elocked_other(struct vnode *vp, const char *str)
{

        if (vp && !IGNORE_LOCK(vp) &&
            VOP_ISLOCKED(vp, curthread) != LK_EXCLOTHER)
                vfs_badlock("is not exclusive locked by another thread",
                    str, vp);
}

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

        if (vp && !IGNORE_LOCK(vp) &&
            VOP_ISLOCKED(vp, curthread) != LK_SHARED)
                vfs_badlock("is not locked shared but should be", str, vp);
}
#endif /* 0 */
#endif /* DEBUG_VFS_LOCKS */

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 != a->a_fdvp)
                ASSERT_VOP_UNLOCKED(a->a_fdvp, "vop_rename: fdvp locked");
        if (a->a_tvp != a->a_fvp)
                ASSERT_VOP_UNLOCKED(a->a_fvp, "vop_rename: tvp 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)
                vholdl(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);
}

void
vop_strategy_pre(void *ap)
{
#ifdef DEBUG_VFS_LOCKS
        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 (BUF_REFCNT(bp) < 1) {
                if (vfs_badlock_print)
                        printf(
                            "VOP_STRATEGY: bp is not locked but should be\n");
                if (vfs_badlock_ddb)
                        kdb_enter("lock violation");
        }
#endif
}

void
vop_lookup_pre(void *ap)
{
#ifdef DEBUG_VFS_LOCKS
        struct vop_lookup_args *a;
        struct vnode *dvp;

        a = ap;
        dvp = a->a_dvp;
        ASSERT_VI_UNLOCKED(dvp, "VOP_LOOKUP");
        ASSERT_VOP_LOCKED(dvp, "VOP_LOOKUP");
#endif
}

void
vop_lookup_post(void *ap, int rc)
{
#ifdef DEBUG_VFS_LOCKS
        struct vop_lookup_args *a;
        struct vnode *dvp;
        struct vnode *vp;

        a = ap;
        dvp = a->a_dvp;
        vp = *(a->a_vpp);

        ASSERT_VI_UNLOCKED(dvp, "VOP_LOOKUP");
        ASSERT_VOP_LOCKED(dvp, "VOP_LOOKUP");

        if (!rc)
                ASSERT_VOP_LOCKED(vp, "VOP_LOOKUP (child)");
#endif
}

void
vop_lock_pre(void *ap)
{
#ifdef DEBUG_VFS_LOCKS
        struct vop_lock_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");
#endif
}

void
vop_lock_post(void *ap, int rc)
{
#ifdef DEBUG_VFS_LOCKS
        struct vop_lock_args *a = ap;

        ASSERT_VI_UNLOCKED(a->a_vp, "VOP_LOCK");
        if (rc == 0)
                ASSERT_VOP_LOCKED(a->a_vp, "VOP_LOCK");
#endif
}

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

        if (a->a_flags & LK_INTERLOCK)
                ASSERT_VI_LOCKED(a->a_vp, "VOP_UNLOCK");
        ASSERT_VOP_LOCKED(a->a_vp, "VOP_UNLOCK");
#endif
}

void
vop_unlock_post(void *ap, int rc)
{
#ifdef DEBUG_VFS_LOCKS
        struct vop_unlock_args *a = ap;

        if (a->a_flags & LK_INTERLOCK)
                ASSERT_VI_UNLOCKED(a->a_vp, "VOP_UNLOCK");
#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_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_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;

        if (!rc) {
                VFS_KNOTE_UNLOCKED(a->a_fdvp, NOTE_WRITE);
                VFS_KNOTE_UNLOCKED(a->a_tdvp, NOTE_WRITE);
                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_symlink_post(void *ap, int rc)
{
        struct vop_symlink_args *a = ap;
        
        if (!rc)
                VFS_KNOTE_LOCKED(a->a_dvp, NOTE_WRITE);
}

static struct knlist fs_knlist;

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

void
vfs_event_signal(fsid_t *fsid, u_int32_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 =
        { 0, filt_fsattach, filt_fsdetach, 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) {
                return (EINVAL);
        }
        VCTLTOREQ(&vc, req);
        return (VFS_SYSCTL(mp, vc.vc_op, req));
}

SYSCTL_PROC(_vfs, OID_AUTO, ctl, 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 =
        { 1, NULL, filt_vfsdetach, filt_vfsread };
static struct filterops vfswrite_filtops =
        { 1, NULL, filt_vfsdetach, filt_vfswrite };
static struct filterops vfsvnode_filtops =
        { 1, NULL, filt_vfsdetach, filt_vfsvnode };

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

        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, curthread);
}

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

        VOP_UNLOCK(vp, 0, curthread);
}

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

        return (VOP_ISLOCKED(vp, curthread) == LK_EXCLUSIVE);
}

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 (1);
        }

        kn->kn_hook = (caddr_t)vp;

        if (vp->v_pollinfo == NULL)
                v_addpollinfo(vp);
        if (vp->v_pollinfo == NULL)
                return (ENOMEM);
        knl = &vp->v_pollinfo->vpi_selinfo.si_note;
        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);
}

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

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

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

        kn->kn_data = va.va_size - kn->kn_fp->f_offset;
        return (kn->kn_data != 0);
}

/*ARGSUSED*/
static int
filt_vfswrite(struct knote *kn, long hint)
{
        /*
         * filesystem is gone, so set the EOF flag and schedule
         * the knote for deletion.
         */
        if (hint == NOTE_REVOKE)
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);

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

static int
filt_vfsvnode(struct knote *kn, long hint)
{
        if (kn->kn_sfflags & hint)
                kn->kn_fflags |= hint;
        if (hint == NOTE_REVOKE) {
                kn->kn_flags |= EV_EOF;
                return (1);
        }
        return (kn->kn_fflags != 0);
}