cache: remove vnode -> path lookup disablement

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

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1989, 1993, 1995
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Poul-Henning Kamp of the FreeBSD Project.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)vfs_cache.c 8.5 (Berkeley) 3/22/95
 */

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

#include "opt_ddb.h"
#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/counter.h>
#include <sys/filedesc.h>
#include <sys/fnv_hash.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/fcntl.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/proc.h>
#include <sys/rwlock.h>
#include <sys/sdt.h>
#include <sys/smp.h>
#include <sys/syscallsubr.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/vnode.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif

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

#include <vm/uma.h>

SDT_PROVIDER_DECLARE(vfs);
SDT_PROBE_DEFINE3(vfs, namecache, enter, done, "struct vnode *", "char *",
    "struct vnode *");
SDT_PROBE_DEFINE2(vfs, namecache, enter_negative, done, "struct vnode *",
    "char *");
SDT_PROBE_DEFINE1(vfs, namecache, fullpath, entry, "struct vnode *");
SDT_PROBE_DEFINE3(vfs, namecache, fullpath, hit, "struct vnode *",
    "char *", "struct vnode *");
SDT_PROBE_DEFINE1(vfs, namecache, fullpath, miss, "struct vnode *");
SDT_PROBE_DEFINE3(vfs, namecache, fullpath, return, "int",
    "struct vnode *", "char *");
SDT_PROBE_DEFINE3(vfs, namecache, lookup, hit, "struct vnode *", "char *",
    "struct vnode *");
SDT_PROBE_DEFINE2(vfs, namecache, lookup, hit__negative,
    "struct vnode *", "char *");
SDT_PROBE_DEFINE2(vfs, namecache, lookup, miss, "struct vnode *",
    "char *");
SDT_PROBE_DEFINE1(vfs, namecache, purge, done, "struct vnode *");
SDT_PROBE_DEFINE1(vfs, namecache, purge_negative, done, "struct vnode *");
SDT_PROBE_DEFINE1(vfs, namecache, purgevfs, done, "struct mount *");
SDT_PROBE_DEFINE3(vfs, namecache, zap, done, "struct vnode *", "char *",
    "struct vnode *");
SDT_PROBE_DEFINE2(vfs, namecache, zap_negative, done, "struct vnode *",
    "char *");
SDT_PROBE_DEFINE2(vfs, namecache, shrink_negative, done, "struct vnode *",
    "char *");

/*
 * This structure describes the elements in the cache of recent
 * names looked up by namei.
 */

struct  namecache {
        LIST_ENTRY(namecache) nc_hash;  /* hash chain */
        LIST_ENTRY(namecache) nc_src;   /* source vnode list */
        TAILQ_ENTRY(namecache) nc_dst;  /* destination vnode list */
        struct  vnode *nc_dvp;          /* vnode of parent of name */
        union {
                struct  vnode *nu_vp;   /* vnode the name refers to */
        } n_un;
        u_char  nc_flag;                /* flag bits */
        u_char  nc_nlen;                /* length of name */
        char    nc_name[0];             /* segment name + nul */
};

/*
 * struct namecache_ts repeats struct namecache layout up to the
 * nc_nlen member.
 * struct namecache_ts is used in place of struct namecache when time(s) need
 * to be stored.  The nc_dotdottime field is used when a cache entry is mapping
 * both a non-dotdot directory name plus dotdot for the directory's
 * parent.
 */
struct  namecache_ts {
        struct  timespec nc_time;       /* timespec provided by fs */
        struct  timespec nc_dotdottime; /* dotdot timespec provided by fs */
        int     nc_ticks;               /* ticks value when entry was added */
        struct namecache nc_nc;
};

#define nc_vp           n_un.nu_vp

/*
 * Flags in namecache.nc_flag
 */
#define NCF_WHITE       0x01
#define NCF_ISDOTDOT    0x02
#define NCF_TS          0x04
#define NCF_DTS         0x08
#define NCF_DVDROP      0x10
#define NCF_NEGATIVE    0x20
#define NCF_HOTNEGATIVE 0x40

/*
 * Name caching works as follows:
 *
 * Names found by directory scans are retained in a cache
 * for future reference.  It is managed LRU, so frequently
 * used names will hang around.  Cache is indexed by hash value
 * obtained from (dvp, name) where dvp refers to the directory
 * containing name.
 *
 * If it is a "negative" entry, (i.e. for a name that is known NOT to
 * exist) the vnode pointer will be NULL.
 *
 * Upon reaching the last segment of a path, if the reference
 * is for DELETE, or NOCACHE is set (rewrite), and the
 * name is located in the cache, it will be dropped.
 *
 * These locks are used (in the order in which they can be taken):
 * NAME         TYPE    ROLE
 * vnodelock    mtx     vnode lists and v_cache_dd field protection
 * bucketlock   rwlock  for access to given set of hash buckets
 * neglist      mtx     negative entry LRU management
 *
 * Additionally, ncneg_shrink_lock mtx is used to have at most one thread
 * shrinking the LRU list.
 *
 * It is legal to take multiple vnodelock and bucketlock locks. The locking
 * order is lower address first. Both are recursive.
 *
 * "." lookups are lockless.
 *
 * ".." and vnode -> name lookups require vnodelock.
 *
 * name -> vnode lookup requires the relevant bucketlock to be held for reading.
 *
 * Insertions and removals of entries require involved vnodes and bucketlocks
 * to be write-locked to prevent other threads from seeing the entry.
 *
 * Some lookups result in removal of the found entry (e.g. getting rid of a
 * negative entry with the intent to create a positive one), which poses a
 * problem when multiple threads reach the state. Similarly, two different
 * threads can purge two different vnodes and try to remove the same name.
 *
 * If the already held vnode lock is lower than the second required lock, we
 * can just take the other lock. However, in the opposite case, this could
 * deadlock. As such, this is resolved by trylocking and if that fails unlocking
 * the first node, locking everything in order and revalidating the state.
 */

/*
 * Structures associated with name caching.
 */
#define NCHHASH(hash) \
        (&nchashtbl[(hash) & nchash])
static __read_mostly LIST_HEAD(nchashhead, namecache) *nchashtbl;/* Hash Table */
static u_long __read_mostly     nchash;                 /* size of hash table */
SYSCTL_ULONG(_debug, OID_AUTO, nchash, CTLFLAG_RD, &nchash, 0,
    "Size of namecache hash table");
static u_long __read_mostly     ncnegfactor = 5; /* ratio of negative entries */
SYSCTL_ULONG(_vfs, OID_AUTO, ncnegfactor, CTLFLAG_RW, &ncnegfactor, 0,
    "Ratio of negative namecache entries");
static u_long __exclusive_cache_line    numneg; /* number of negative entries allocated */
static u_long __exclusive_cache_line    numcache;/* number of cache entries allocated */
u_int ncsizefactor = 2;
SYSCTL_UINT(_vfs, OID_AUTO, ncsizefactor, CTLFLAG_RW, &ncsizefactor, 0,
    "Size factor for namecache");
static u_int __read_mostly      ncpurgeminvnodes;
SYSCTL_UINT(_vfs, OID_AUTO, ncpurgeminvnodes, CTLFLAG_RW, &ncpurgeminvnodes, 0,
    "Number of vnodes below which purgevfs ignores the request");
static u_int __read_mostly      ncsize; /* the size as computed on creation or resizing */

struct nchstats nchstats;               /* cache effectiveness statistics */

static struct mtx __exclusive_cache_line        ncneg_shrink_lock;
static int      shrink_list_turn;

struct neglist {
        struct mtx              nl_lock;
        TAILQ_HEAD(, namecache) nl_list;
} __aligned(CACHE_LINE_SIZE);

static struct neglist __read_mostly     *neglists;
static struct neglist ncneg_hot;
static u_long numhotneg;

#define numneglists (ncneghash + 1)
static u_int __read_mostly      ncneghash;
static inline struct neglist *
NCP2NEGLIST(struct namecache *ncp)
{

        return (&neglists[(((uintptr_t)(ncp) >> 8) & ncneghash)]);
}

#define numbucketlocks (ncbuckethash + 1)
static u_int __read_mostly  ncbuckethash;
static struct rwlock_padalign __read_mostly  *bucketlocks;
#define HASH2BUCKETLOCK(hash) \
        ((struct rwlock *)(&bucketlocks[((hash) & ncbuckethash)]))

#define numvnodelocks (ncvnodehash + 1)
static u_int __read_mostly  ncvnodehash;
static struct mtx __read_mostly *vnodelocks;
static inline struct mtx *
VP2VNODELOCK(struct vnode *vp)
{

        return (&vnodelocks[(((uintptr_t)(vp) >> 8) & ncvnodehash)]);
}

/*
 * UMA zones for the VFS cache.
 *
 * The small cache is used for entries with short names, which are the
 * most common.  The large cache is used for entries which are too big to
 * fit in the small cache.
 */
static uma_zone_t __read_mostly cache_zone_small;
static uma_zone_t __read_mostly cache_zone_small_ts;
static uma_zone_t __read_mostly cache_zone_large;
static uma_zone_t __read_mostly cache_zone_large_ts;

#define CACHE_PATH_CUTOFF       35

static struct namecache *
cache_alloc(int len, int ts)
{
        struct namecache_ts *ncp_ts;
        struct namecache *ncp;

        if (__predict_false(ts)) {
                if (len <= CACHE_PATH_CUTOFF)
                        ncp_ts = uma_zalloc(cache_zone_small_ts, M_WAITOK);
                else
                        ncp_ts = uma_zalloc(cache_zone_large_ts, M_WAITOK);
                ncp = &ncp_ts->nc_nc;
        } else {
                if (len <= CACHE_PATH_CUTOFF)
                        ncp = uma_zalloc(cache_zone_small, M_WAITOK);
                else
                        ncp = uma_zalloc(cache_zone_large, M_WAITOK);
        }
        return (ncp);
}

static void
cache_free(struct namecache *ncp)
{
        struct namecache_ts *ncp_ts;

        if (ncp == NULL)
                return;
        if ((ncp->nc_flag & NCF_DVDROP) != 0)
                vdrop(ncp->nc_dvp);
        if (__predict_false(ncp->nc_flag & NCF_TS)) {
                ncp_ts = __containerof(ncp, struct namecache_ts, nc_nc);
                if (ncp->nc_nlen <= CACHE_PATH_CUTOFF)
                        uma_zfree(cache_zone_small_ts, ncp_ts);
                else
                        uma_zfree(cache_zone_large_ts, ncp_ts);
        } else {
                if (ncp->nc_nlen <= CACHE_PATH_CUTOFF)
                        uma_zfree(cache_zone_small, ncp);
                else
                        uma_zfree(cache_zone_large, ncp);
        }
}

static void
cache_out_ts(struct namecache *ncp, struct timespec *tsp, int *ticksp)
{
        struct namecache_ts *ncp_ts;

        KASSERT((ncp->nc_flag & NCF_TS) != 0 ||
            (tsp == NULL && ticksp == NULL),
            ("No NCF_TS"));

        if (tsp == NULL && ticksp == NULL)
                return;

        ncp_ts = __containerof(ncp, struct namecache_ts, nc_nc);
        if (tsp != NULL)
                *tsp = ncp_ts->nc_time;
        if (ticksp != NULL)
                *ticksp = ncp_ts->nc_ticks;
}

#ifdef DEBUG_CACHE
static int __read_mostly        doingcache = 1; /* 1 => enable the cache */
SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
    "VFS namecache enabled");
#endif

/* Export size information to userland */
SYSCTL_INT(_debug_sizeof, OID_AUTO, namecache, CTLFLAG_RD, SYSCTL_NULL_INT_PTR,
    sizeof(struct namecache), "sizeof(struct namecache)");

/*
 * The new name cache statistics
 */
static SYSCTL_NODE(_vfs, OID_AUTO, cache, CTLFLAG_RW, 0,
    "Name cache statistics");
#define STATNODE_ULONG(name, descr)     \
        SYSCTL_ULONG(_vfs_cache, OID_AUTO, name, CTLFLAG_RD, &name, 0, descr);
#define STATNODE_COUNTER(name, descr)   \
        static counter_u64_t __read_mostly name; \
        SYSCTL_COUNTER_U64(_vfs_cache, OID_AUTO, name, CTLFLAG_RD, &name, descr);
STATNODE_ULONG(numneg, "Number of negative cache entries");
STATNODE_ULONG(numcache, "Number of cache entries");
STATNODE_COUNTER(numcachehv, "Number of namecache entries with vnodes held");
STATNODE_COUNTER(numcalls, "Number of cache lookups");
STATNODE_COUNTER(dothits, "Number of '.' hits");
STATNODE_COUNTER(dotdothits, "Number of '..' hits");
STATNODE_COUNTER(numchecks, "Number of checks in lookup");
STATNODE_COUNTER(nummiss, "Number of cache misses");
STATNODE_COUNTER(nummisszap, "Number of cache misses we do not want to cache");
STATNODE_COUNTER(numposzaps,
    "Number of cache hits (positive) we do not want to cache");
STATNODE_COUNTER(numposhits, "Number of cache hits (positive)");
STATNODE_COUNTER(numnegzaps,
    "Number of cache hits (negative) we do not want to cache");
STATNODE_COUNTER(numneghits, "Number of cache hits (negative)");
/* These count for kern___getcwd(), too. */
STATNODE_COUNTER(numfullpathcalls, "Number of fullpath search calls");
STATNODE_COUNTER(numfullpathfail1, "Number of fullpath search errors (ENOTDIR)");
STATNODE_COUNTER(numfullpathfail2,
    "Number of fullpath search errors (VOP_VPTOCNP failures)");
STATNODE_COUNTER(numfullpathfail4, "Number of fullpath search errors (ENOMEM)");
STATNODE_COUNTER(numfullpathfound, "Number of successful fullpath calls");
STATNODE_COUNTER(zap_and_exit_bucket_relock_success,
    "Number of successful removals after relocking");
static long zap_and_exit_bucket_fail; STATNODE_ULONG(zap_and_exit_bucket_fail,
    "Number of times zap_and_exit failed to lock");
static long zap_and_exit_bucket_fail2; STATNODE_ULONG(zap_and_exit_bucket_fail2,
    "Number of times zap_and_exit failed to lock");
static long cache_lock_vnodes_cel_3_failures;
STATNODE_ULONG(cache_lock_vnodes_cel_3_failures,
    "Number of times 3-way vnode locking failed");
STATNODE_ULONG(numhotneg, "Number of hot negative entries");
STATNODE_COUNTER(numneg_evicted,
    "Number of negative entries evicted when adding a new entry");
STATNODE_COUNTER(shrinking_skipped,
    "Number of times shrinking was already in progress");

static void cache_zap_locked(struct namecache *ncp, bool neg_locked);
static int vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
    char *buf, char **retbuf, size_t buflen);

static MALLOC_DEFINE(M_VFSCACHE, "vfscache", "VFS name cache entries");

static int cache_yield;
SYSCTL_INT(_vfs_cache, OID_AUTO, yield, CTLFLAG_RD, &cache_yield, 0,
    "Number of times cache called yield");

static void __noinline
cache_maybe_yield(void)
{

        if (should_yield()) {
                cache_yield++;
                kern_yield(PRI_USER);
        }
}

static inline void
cache_assert_vlp_locked(struct mtx *vlp)
{

        if (vlp != NULL)
                mtx_assert(vlp, MA_OWNED);
}

static inline void
cache_assert_vnode_locked(struct vnode *vp)
{
        struct mtx *vlp;

        vlp = VP2VNODELOCK(vp);
        cache_assert_vlp_locked(vlp);
}

static uint32_t
cache_get_hash(char *name, u_char len, struct vnode *dvp)
{
        uint32_t hash;

        hash = fnv_32_buf(name, len, FNV1_32_INIT);
        hash = fnv_32_buf(&dvp, sizeof(dvp), hash);
        return (hash);
}

static inline struct rwlock *
NCP2BUCKETLOCK(struct namecache *ncp)
{
        uint32_t hash;

        hash = cache_get_hash(ncp->nc_name, ncp->nc_nlen, ncp->nc_dvp);
        return (HASH2BUCKETLOCK(hash));
}

#ifdef INVARIANTS
static void
cache_assert_bucket_locked(struct namecache *ncp, int mode)
{
        struct rwlock *blp;

        blp = NCP2BUCKETLOCK(ncp);
        rw_assert(blp, mode);
}
#else
#define cache_assert_bucket_locked(x, y) do { } while (0)
#endif

#define cache_sort_vnodes(x, y) _cache_sort_vnodes((void **)(x), (void **)(y))
static void
_cache_sort_vnodes(void **p1, void **p2)
{
        void *tmp;

        MPASS(*p1 != NULL || *p2 != NULL);

        if (*p1 > *p2) {
                tmp = *p2;
                *p2 = *p1;
                *p1 = tmp;
        }
}

static void
cache_lock_all_buckets(void)
{
        u_int i;

        for (i = 0; i < numbucketlocks; i++)
                rw_wlock(&bucketlocks[i]);
}

static void
cache_unlock_all_buckets(void)
{
        u_int i;

        for (i = 0; i < numbucketlocks; i++)
                rw_wunlock(&bucketlocks[i]);
}

static void
cache_lock_all_vnodes(void)
{
        u_int i;

        for (i = 0; i < numvnodelocks; i++)
                mtx_lock(&vnodelocks[i]);
}

static void
cache_unlock_all_vnodes(void)
{
        u_int i;

        for (i = 0; i < numvnodelocks; i++)
                mtx_unlock(&vnodelocks[i]);
}

static int
cache_trylock_vnodes(struct mtx *vlp1, struct mtx *vlp2)
{

        cache_sort_vnodes(&vlp1, &vlp2);

        if (vlp1 != NULL) {
                if (!mtx_trylock(vlp1))
                        return (EAGAIN);
        }
        if (!mtx_trylock(vlp2)) {
                if (vlp1 != NULL)
                        mtx_unlock(vlp1);
                return (EAGAIN);
        }

        return (0);
}

static void
cache_lock_vnodes(struct mtx *vlp1, struct mtx *vlp2)
{

        MPASS(vlp1 != NULL || vlp2 != NULL);
        MPASS(vlp1 <= vlp2);

        if (vlp1 != NULL)
                mtx_lock(vlp1);
        if (vlp2 != NULL)
                mtx_lock(vlp2);
}

static void
cache_unlock_vnodes(struct mtx *vlp1, struct mtx *vlp2)
{

        MPASS(vlp1 != NULL || vlp2 != NULL);

        if (vlp1 != NULL)
                mtx_unlock(vlp1);
        if (vlp2 != NULL)
                mtx_unlock(vlp2);
}

static int
sysctl_nchstats(SYSCTL_HANDLER_ARGS)
{
        struct nchstats snap;

        if (req->oldptr == NULL)
                return (SYSCTL_OUT(req, 0, sizeof(snap)));

        snap = nchstats;
        snap.ncs_goodhits = counter_u64_fetch(numposhits);
        snap.ncs_neghits = counter_u64_fetch(numneghits);
        snap.ncs_badhits = counter_u64_fetch(numposzaps) +
            counter_u64_fetch(numnegzaps);
        snap.ncs_miss = counter_u64_fetch(nummisszap) +
            counter_u64_fetch(nummiss);

        return (SYSCTL_OUT(req, &snap, sizeof(snap)));
}
SYSCTL_PROC(_vfs_cache, OID_AUTO, nchstats, CTLTYPE_OPAQUE | CTLFLAG_RD |
    CTLFLAG_MPSAFE, 0, 0, sysctl_nchstats, "LU",
    "VFS cache effectiveness statistics");

#ifdef DIAGNOSTIC
/*
 * Grab an atomic snapshot of the name cache hash chain lengths
 */
static SYSCTL_NODE(_debug, OID_AUTO, hashstat, CTLFLAG_RW, NULL,
    "hash table stats");

static int
sysctl_debug_hashstat_rawnchash(SYSCTL_HANDLER_ARGS)
{
        struct nchashhead *ncpp;
        struct namecache *ncp;
        int i, error, n_nchash, *cntbuf;

retry:
        n_nchash = nchash + 1;  /* nchash is max index, not count */
        if (req->oldptr == NULL)
                return SYSCTL_OUT(req, 0, n_nchash * sizeof(int));
        cntbuf = malloc(n_nchash * sizeof(int), M_TEMP, M_ZERO | M_WAITOK);
        cache_lock_all_buckets();
        if (n_nchash != nchash + 1) {
                cache_unlock_all_buckets();
                free(cntbuf, M_TEMP);
                goto retry;
        }
        /* Scan hash tables counting entries */
        for (ncpp = nchashtbl, i = 0; i < n_nchash; ncpp++, i++)
                LIST_FOREACH(ncp, ncpp, nc_hash)
                        cntbuf[i]++;
        cache_unlock_all_buckets();
        for (error = 0, i = 0; i < n_nchash; i++)
                if ((error = SYSCTL_OUT(req, &cntbuf[i], sizeof(int))) != 0)
                        break;
        free(cntbuf, M_TEMP);
        return (error);
}
SYSCTL_PROC(_debug_hashstat, OID_AUTO, rawnchash, CTLTYPE_INT|CTLFLAG_RD|
    CTLFLAG_MPSAFE, 0, 0, sysctl_debug_hashstat_rawnchash, "S,int",
    "nchash chain lengths");

static int
sysctl_debug_hashstat_nchash(SYSCTL_HANDLER_ARGS)
{
        int error;
        struct nchashhead *ncpp;
        struct namecache *ncp;
        int n_nchash;
        int count, maxlength, used, pct;

        if (!req->oldptr)
                return SYSCTL_OUT(req, 0, 4 * sizeof(int));

        cache_lock_all_buckets();
        n_nchash = nchash + 1;  /* nchash is max index, not count */
        used = 0;
        maxlength = 0;

        /* Scan hash tables for applicable entries */
        for (ncpp = nchashtbl; n_nchash > 0; n_nchash--, ncpp++) {
                count = 0;
                LIST_FOREACH(ncp, ncpp, nc_hash) {
                        count++;
                }
                if (count)
                        used++;
                if (maxlength < count)
                        maxlength = count;
        }
        n_nchash = nchash + 1;
        cache_unlock_all_buckets();
        pct = (used * 100) / (n_nchash / 100);
        error = SYSCTL_OUT(req, &n_nchash, sizeof(n_nchash));
        if (error)
                return (error);
        error = SYSCTL_OUT(req, &used, sizeof(used));
        if (error)
                return (error);
        error = SYSCTL_OUT(req, &maxlength, sizeof(maxlength));
        if (error)
                return (error);
        error = SYSCTL_OUT(req, &pct, sizeof(pct));
        if (error)
                return (error);
        return (0);
}
SYSCTL_PROC(_debug_hashstat, OID_AUTO, nchash, CTLTYPE_INT|CTLFLAG_RD|
    CTLFLAG_MPSAFE, 0, 0, sysctl_debug_hashstat_nchash, "I",
    "nchash statistics (number of total/used buckets, maximum chain length, usage percentage)");
#endif

/*
 * Negative entries management
 *
 * A variation of LRU scheme is used. New entries are hashed into one of
 * numneglists cold lists. Entries get promoted to the hot list on first hit.
 *
 * The shrinker will demote hot list head and evict from the cold list in a
 * round-robin manner.
 */
static void
cache_negative_hit(struct namecache *ncp)
{
        struct neglist *neglist;

        MPASS(ncp->nc_flag & NCF_NEGATIVE);
        if (ncp->nc_flag & NCF_HOTNEGATIVE)
                return;
        neglist = NCP2NEGLIST(ncp);
        mtx_lock(&ncneg_hot.nl_lock);
        mtx_lock(&neglist->nl_lock);
        if (!(ncp->nc_flag & NCF_HOTNEGATIVE)) {
                numhotneg++;
                TAILQ_REMOVE(&neglist->nl_list, ncp, nc_dst);
                TAILQ_INSERT_TAIL(&ncneg_hot.nl_list, ncp, nc_dst);
                ncp->nc_flag |= NCF_HOTNEGATIVE;
        }
        mtx_unlock(&neglist->nl_lock);
        mtx_unlock(&ncneg_hot.nl_lock);
}

static void
cache_negative_insert(struct namecache *ncp, bool neg_locked)
{
        struct neglist *neglist;

        MPASS(ncp->nc_flag & NCF_NEGATIVE);
        cache_assert_bucket_locked(ncp, RA_WLOCKED);
        neglist = NCP2NEGLIST(ncp);
        if (!neg_locked) {
                mtx_lock(&neglist->nl_lock);
        } else {
                mtx_assert(&neglist->nl_lock, MA_OWNED);
        }
        TAILQ_INSERT_TAIL(&neglist->nl_list, ncp, nc_dst);
        if (!neg_locked)
                mtx_unlock(&neglist->nl_lock);
        atomic_add_rel_long(&numneg, 1);
}

static void
cache_negative_remove(struct namecache *ncp, bool neg_locked)
{
        struct neglist *neglist;
        bool hot_locked = false;
        bool list_locked = false;

        MPASS(ncp->nc_flag & NCF_NEGATIVE);
        cache_assert_bucket_locked(ncp, RA_WLOCKED);
        neglist = NCP2NEGLIST(ncp);
        if (!neg_locked) {
                if (ncp->nc_flag & NCF_HOTNEGATIVE) {
                        hot_locked = true;
                        mtx_lock(&ncneg_hot.nl_lock);
                        if (!(ncp->nc_flag & NCF_HOTNEGATIVE)) {
                                list_locked = true;
                                mtx_lock(&neglist->nl_lock);
                        }
                } else {
                        list_locked = true;
                        mtx_lock(&neglist->nl_lock);
                }
        }
        if (ncp->nc_flag & NCF_HOTNEGATIVE) {
                mtx_assert(&ncneg_hot.nl_lock, MA_OWNED);
                TAILQ_REMOVE(&ncneg_hot.nl_list, ncp, nc_dst);
                numhotneg--;
        } else {
                mtx_assert(&neglist->nl_lock, MA_OWNED);
                TAILQ_REMOVE(&neglist->nl_list, ncp, nc_dst);
        }
        if (list_locked)
                mtx_unlock(&neglist->nl_lock);
        if (hot_locked)
                mtx_unlock(&ncneg_hot.nl_lock);
        atomic_subtract_rel_long(&numneg, 1);
}

static void
cache_negative_shrink_select(int start, struct namecache **ncpp,
    struct neglist **neglistpp)
{
        struct neglist *neglist;
        struct namecache *ncp;
        int i;

        *ncpp = ncp = NULL;
        neglist = NULL;

        for (i = start; i < numneglists; i++) {
                neglist = &neglists[i];
                if (TAILQ_FIRST(&neglist->nl_list) == NULL)
                        continue;
                mtx_lock(&neglist->nl_lock);
                ncp = TAILQ_FIRST(&neglist->nl_list);
                if (ncp != NULL)
                        break;
                mtx_unlock(&neglist->nl_lock);
        }

        *neglistpp = neglist;
        *ncpp = ncp;
}

static void
cache_negative_zap_one(void)
{
        struct namecache *ncp, *ncp2;
        struct neglist *neglist;
        struct mtx *dvlp;
        struct rwlock *blp;

        if (mtx_owner(&ncneg_shrink_lock) != NULL ||
            !mtx_trylock(&ncneg_shrink_lock)) {
                counter_u64_add(shrinking_skipped, 1);
                return;
        }

        mtx_lock(&ncneg_hot.nl_lock);
        ncp = TAILQ_FIRST(&ncneg_hot.nl_list);
        if (ncp != NULL) {
                neglist = NCP2NEGLIST(ncp);
                mtx_lock(&neglist->nl_lock);
                TAILQ_REMOVE(&ncneg_hot.nl_list, ncp, nc_dst);
                TAILQ_INSERT_TAIL(&neglist->nl_list, ncp, nc_dst);
                ncp->nc_flag &= ~NCF_HOTNEGATIVE;
                numhotneg--;
                mtx_unlock(&neglist->nl_lock);
        }
        mtx_unlock(&ncneg_hot.nl_lock);

        cache_negative_shrink_select(shrink_list_turn, &ncp, &neglist);
        shrink_list_turn++;
        if (shrink_list_turn == numneglists)
                shrink_list_turn = 0;
        if (ncp == NULL && shrink_list_turn == 0)
                cache_negative_shrink_select(shrink_list_turn, &ncp, &neglist);
        mtx_unlock(&ncneg_shrink_lock);
        if (ncp == NULL)
                return;

        MPASS(ncp->nc_flag & NCF_NEGATIVE);
        dvlp = VP2VNODELOCK(ncp->nc_dvp);
        blp = NCP2BUCKETLOCK(ncp);
        mtx_unlock(&neglist->nl_lock);
        mtx_lock(dvlp);
        rw_wlock(blp);
        mtx_lock(&neglist->nl_lock);
        ncp2 = TAILQ_FIRST(&neglist->nl_list);
        if (ncp != ncp2 || dvlp != VP2VNODELOCK(ncp2->nc_dvp) ||
            blp != NCP2BUCKETLOCK(ncp2) || !(ncp2->nc_flag & NCF_NEGATIVE)) {
                ncp = NULL;
        } else {
                SDT_PROBE2(vfs, namecache, shrink_negative, done, ncp->nc_dvp,
                    ncp->nc_name);

                cache_zap_locked(ncp, true);
                counter_u64_add(numneg_evicted, 1);
        }
        mtx_unlock(&neglist->nl_lock);
        rw_wunlock(blp);
        mtx_unlock(dvlp);
        cache_free(ncp);
}

/*
 * cache_zap_locked():
 *
 *   Removes a namecache entry from cache, whether it contains an actual
 *   pointer to a vnode or if it is just a negative cache entry.
 */
static void
cache_zap_locked(struct namecache *ncp, bool neg_locked)
{

        if (!(ncp->nc_flag & NCF_NEGATIVE))
                cache_assert_vnode_locked(ncp->nc_vp);
        cache_assert_vnode_locked(ncp->nc_dvp);
        cache_assert_bucket_locked(ncp, RA_WLOCKED);

        CTR2(KTR_VFS, "cache_zap(%p) vp %p", ncp,
            (ncp->nc_flag & NCF_NEGATIVE) ? NULL : ncp->nc_vp);
        LIST_REMOVE(ncp, nc_hash);
        if (!(ncp->nc_flag & NCF_NEGATIVE)) {
                SDT_PROBE3(vfs, namecache, zap, done, ncp->nc_dvp,
                    ncp->nc_name, ncp->nc_vp);
                TAILQ_REMOVE(&ncp->nc_vp->v_cache_dst, ncp, nc_dst);
                if (ncp == ncp->nc_vp->v_cache_dd)
                        ncp->nc_vp->v_cache_dd = NULL;
        } else {
                SDT_PROBE2(vfs, namecache, zap_negative, done, ncp->nc_dvp,
                    ncp->nc_name);
                cache_negative_remove(ncp, neg_locked);
        }
        if (ncp->nc_flag & NCF_ISDOTDOT) {
                if (ncp == ncp->nc_dvp->v_cache_dd)
                        ncp->nc_dvp->v_cache_dd = NULL;
        } else {
                LIST_REMOVE(ncp, nc_src);
                if (LIST_EMPTY(&ncp->nc_dvp->v_cache_src)) {
                        ncp->nc_flag |= NCF_DVDROP;
                        counter_u64_add(numcachehv, -1);
                }
        }
        atomic_subtract_rel_long(&numcache, 1);
}

static void
cache_zap_negative_locked_vnode_kl(struct namecache *ncp, struct vnode *vp)
{
        struct rwlock *blp;

        MPASS(ncp->nc_dvp == vp);
        MPASS(ncp->nc_flag & NCF_NEGATIVE);
        cache_assert_vnode_locked(vp);

        blp = NCP2BUCKETLOCK(ncp);
        rw_wlock(blp);
        cache_zap_locked(ncp, false);
        rw_wunlock(blp);
}

static bool
cache_zap_locked_vnode_kl2(struct namecache *ncp, struct vnode *vp,
    struct mtx **vlpp)
{
        struct mtx *pvlp, *vlp1, *vlp2, *to_unlock;
        struct rwlock *blp;

        MPASS(vp == ncp->nc_dvp || vp == ncp->nc_vp);
        cache_assert_vnode_locked(vp);

        if (ncp->nc_flag & NCF_NEGATIVE) {
                if (*vlpp != NULL) {
                        mtx_unlock(*vlpp);
                        *vlpp = NULL;
                }
                cache_zap_negative_locked_vnode_kl(ncp, vp);
                return (true);
        }

        pvlp = VP2VNODELOCK(vp);
        blp = NCP2BUCKETLOCK(ncp);
        vlp1 = VP2VNODELOCK(ncp->nc_dvp);
        vlp2 = VP2VNODELOCK(ncp->nc_vp);

        if (*vlpp == vlp1 || *vlpp == vlp2) {
                to_unlock = *vlpp;
                *vlpp = NULL;
        } else {
                if (*vlpp != NULL) {
                        mtx_unlock(*vlpp);
                        *vlpp = NULL;
                }
                cache_sort_vnodes(&vlp1, &vlp2);
                if (vlp1 == pvlp) {
                        mtx_lock(vlp2);
                        to_unlock = vlp2;
                } else {
                        if (!mtx_trylock(vlp1))
                                goto out_relock;
                        to_unlock = vlp1;
                }
        }
        rw_wlock(blp);
        cache_zap_locked(ncp, false);
        rw_wunlock(blp);
        if (to_unlock != NULL)
                mtx_unlock(to_unlock);
        return (true);

out_relock:
        mtx_unlock(vlp2);
        mtx_lock(vlp1);
        mtx_lock(vlp2);
        MPASS(*vlpp == NULL);
        *vlpp = vlp1;
        return (false);
}

static int __noinline
cache_zap_locked_vnode(struct namecache *ncp, struct vnode *vp)
{
        struct mtx *pvlp, *vlp1, *vlp2, *to_unlock;
        struct rwlock *blp;
        int error = 0;

        MPASS(vp == ncp->nc_dvp || vp == ncp->nc_vp);
        cache_assert_vnode_locked(vp);

        pvlp = VP2VNODELOCK(vp);
        if (ncp->nc_flag & NCF_NEGATIVE) {
                cache_zap_negative_locked_vnode_kl(ncp, vp);
                goto out;
        }

        blp = NCP2BUCKETLOCK(ncp);
        vlp1 = VP2VNODELOCK(ncp->nc_dvp);
        vlp2 = VP2VNODELOCK(ncp->nc_vp);
        cache_sort_vnodes(&vlp1, &vlp2);
        if (vlp1 == pvlp) {
                mtx_lock(vlp2);
                to_unlock = vlp2;
        } else {
                if (!mtx_trylock(vlp1)) {
                        error = EAGAIN;
                        goto out;
                }
                to_unlock = vlp1;
        }
        rw_wlock(blp);
        cache_zap_locked(ncp, false);
        rw_wunlock(blp);
        mtx_unlock(to_unlock);
out:
        mtx_unlock(pvlp);
        return (error);
}

/*
 * If trylocking failed we can get here. We know enough to take all needed locks
 * in the right order and re-lookup the entry.
 */
static int
cache_zap_unlocked_bucket(struct namecache *ncp, struct componentname *cnp,
    struct vnode *dvp, struct mtx *dvlp, struct mtx *vlp, uint32_t hash,
    struct rwlock *blp)
{
        struct namecache *rncp;

        cache_assert_bucket_locked(ncp, RA_UNLOCKED);

        cache_sort_vnodes(&dvlp, &vlp);
        cache_lock_vnodes(dvlp, vlp);
        rw_wlock(blp);
        LIST_FOREACH(rncp, (NCHHASH(hash)), nc_hash) {
                if (rncp == ncp && rncp->nc_dvp == dvp &&
                    rncp->nc_nlen == cnp->cn_namelen &&
                    !bcmp(rncp->nc_name, cnp->cn_nameptr, rncp->nc_nlen))
                        break;
        }
        if (rncp != NULL) {
                cache_zap_locked(rncp, false);
                rw_wunlock(blp);
                cache_unlock_vnodes(dvlp, vlp);
                counter_u64_add(zap_and_exit_bucket_relock_success, 1);
                return (0);
        }

        rw_wunlock(blp);
        cache_unlock_vnodes(dvlp, vlp);
        return (EAGAIN);
}

static int __noinline
cache_zap_wlocked_bucket(struct namecache *ncp, struct componentname *cnp,
    uint32_t hash, struct rwlock *blp)
{
        struct mtx *dvlp, *vlp;
        struct vnode *dvp;

        cache_assert_bucket_locked(ncp, RA_WLOCKED);

        dvlp = VP2VNODELOCK(ncp->nc_dvp);
        vlp = NULL;
        if (!(ncp->nc_flag & NCF_NEGATIVE))
                vlp = VP2VNODELOCK(ncp->nc_vp);
        if (cache_trylock_vnodes(dvlp, vlp) == 0) {
                cache_zap_locked(ncp, false);
                rw_wunlock(blp);
                cache_unlock_vnodes(dvlp, vlp);
                return (0);
        }

        dvp = ncp->nc_dvp;
        rw_wunlock(blp);
        return (cache_zap_unlocked_bucket(ncp, cnp, dvp, dvlp, vlp, hash, blp));
}

static int __noinline
cache_zap_rlocked_bucket(struct namecache *ncp, struct componentname *cnp,
    uint32_t hash, struct rwlock *blp)
{
        struct mtx *dvlp, *vlp;
        struct vnode *dvp;

        cache_assert_bucket_locked(ncp, RA_RLOCKED);

        dvlp = VP2VNODELOCK(ncp->nc_dvp);
        vlp = NULL;
        if (!(ncp->nc_flag & NCF_NEGATIVE))
                vlp = VP2VNODELOCK(ncp->nc_vp);
        if (cache_trylock_vnodes(dvlp, vlp) == 0) {
                rw_runlock(blp);
                rw_wlock(blp);
                cache_zap_locked(ncp, false);
                rw_wunlock(blp);
                cache_unlock_vnodes(dvlp, vlp);
                return (0);
        }

        dvp = ncp->nc_dvp;
        rw_runlock(blp);
        return (cache_zap_unlocked_bucket(ncp, cnp, dvp, dvlp, vlp, hash, blp));
}

static int
cache_zap_wlocked_bucket_kl(struct namecache *ncp, struct rwlock *blp,
    struct mtx **vlpp1, struct mtx **vlpp2)
{
        struct mtx *dvlp, *vlp;

        cache_assert_bucket_locked(ncp, RA_WLOCKED);

        dvlp = VP2VNODELOCK(ncp->nc_dvp);
        vlp = NULL;
        if (!(ncp->nc_flag & NCF_NEGATIVE))
                vlp = VP2VNODELOCK(ncp->nc_vp);
        cache_sort_vnodes(&dvlp, &vlp);

        if (*vlpp1 == dvlp && *vlpp2 == vlp) {
                cache_zap_locked(ncp, false);
                cache_unlock_vnodes(dvlp, vlp);
                *vlpp1 = NULL;
                *vlpp2 = NULL;
                return (0);
        }

        if (*vlpp1 != NULL)
                mtx_unlock(*vlpp1);
        if (*vlpp2 != NULL)
                mtx_unlock(*vlpp2);
        *vlpp1 = NULL;
        *vlpp2 = NULL;

        if (cache_trylock_vnodes(dvlp, vlp) == 0) {
                cache_zap_locked(ncp, false);
                cache_unlock_vnodes(dvlp, vlp);
                return (0);
        }

        rw_wunlock(blp);
        *vlpp1 = dvlp;
        *vlpp2 = vlp;
        if (*vlpp1 != NULL)
                mtx_lock(*vlpp1);
        mtx_lock(*vlpp2);
        rw_wlock(blp);
        return (EAGAIN);
}

static void
cache_lookup_unlock(struct rwlock *blp, struct mtx *vlp)
{

        if (blp != NULL) {
                rw_runlock(blp);
        } else {
                mtx_unlock(vlp);
        }
}

static int __noinline
cache_lookup_dot(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp,
    struct timespec *tsp, int *ticksp)
{
        int ltype;

        *vpp = dvp;
        CTR2(KTR_VFS, "cache_lookup(%p, %s) found via .",
                        dvp, cnp->cn_nameptr);
        counter_u64_add(dothits, 1);
        SDT_PROBE3(vfs, namecache, lookup, hit, dvp, ".", *vpp);
        if (tsp != NULL)
                timespecclear(tsp);
        if (ticksp != NULL)
                *ticksp = ticks;
        vrefact(*vpp);
        /*
         * When we lookup "." we still can be asked to lock it
         * differently...
         */
        ltype = cnp->cn_lkflags & LK_TYPE_MASK;
        if (ltype != VOP_ISLOCKED(*vpp)) {
                if (ltype == LK_EXCLUSIVE) {
                        vn_lock(*vpp, LK_UPGRADE | LK_RETRY);
                        if (VN_IS_DOOMED((*vpp))) {
                                /* forced unmount */
                                vrele(*vpp);
                                *vpp = NULL;
                                return (ENOENT);
                        }
                } else
                        vn_lock(*vpp, LK_DOWNGRADE | LK_RETRY);
        }
        return (-1);
}

static __noinline int
cache_lookup_nomakeentry(struct vnode *dvp, struct vnode **vpp,
    struct componentname *cnp, struct timespec *tsp, int *ticksp)
{
        struct namecache *ncp;
        struct rwlock *blp;
        struct mtx *dvlp, *dvlp2;
        uint32_t hash;
        int error;

        if (cnp->cn_namelen == 2 &&
            cnp->cn_nameptr[0] == '.' && cnp->cn_nameptr[1] == '.') {
                counter_u64_add(dotdothits, 1);
                dvlp = VP2VNODELOCK(dvp);
                dvlp2 = NULL;
                mtx_lock(dvlp);
retry_dotdot:
                ncp = dvp->v_cache_dd;
                if (ncp == NULL) {
                        SDT_PROBE3(vfs, namecache, lookup, miss, dvp,
                            "..", NULL);
                        mtx_unlock(dvlp);
                        if (dvlp2 != NULL)
                                mtx_unlock(dvlp2);
                        return (0);
                }
                if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) {
                        if (ncp->nc_dvp != dvp)
                                panic("dvp %p v_cache_dd %p\n", dvp, ncp);
                        if (!cache_zap_locked_vnode_kl2(ncp,
                            dvp, &dvlp2))
                                goto retry_dotdot;
                        MPASS(dvp->v_cache_dd == NULL);
                        mtx_unlock(dvlp);
                        if (dvlp2 != NULL)
                                mtx_unlock(dvlp2);
                        cache_free(ncp);
                } else {
                        dvp->v_cache_dd = NULL;
                        mtx_unlock(dvlp);
                        if (dvlp2 != NULL)
                                mtx_unlock(dvlp2);
                }
                return (0);
        }

        hash = cache_get_hash(cnp->cn_nameptr, cnp->cn_namelen, dvp);
        blp = HASH2BUCKETLOCK(hash);
retry:
        if (LIST_EMPTY(NCHHASH(hash)))
                goto out_no_entry;

        rw_wlock(blp);

        LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
                counter_u64_add(numchecks, 1);
                if (ncp->nc_dvp == dvp && ncp->nc_nlen == cnp->cn_namelen &&
                    !bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen))
                        break;
        }

        /* We failed to find an entry */
        if (ncp == NULL) {
                rw_wunlock(blp);
                goto out_no_entry;
        }

        error = cache_zap_wlocked_bucket(ncp, cnp, hash, blp);
        if (__predict_false(error != 0)) {
                zap_and_exit_bucket_fail++;
                cache_maybe_yield();
                goto retry;
        }
        counter_u64_add(numposzaps, 1);
        cache_free(ncp);
        return (0);
out_no_entry:
        SDT_PROBE3(vfs, namecache, lookup, miss, dvp, cnp->cn_nameptr, NULL);
        counter_u64_add(nummisszap, 1);
        return (0);
}

/**
 * Lookup a name in the name cache
 *
 * # Arguments
 *
 * - dvp:       Parent directory in which to search.
 * - vpp:       Return argument.  Will contain desired vnode on cache hit.
 * - cnp:       Parameters of the name search.  The most interesting bits of
 *              the cn_flags field have the following meanings:
 *      - MAKEENTRY:    If clear, free an entry from the cache rather than look
 *                      it up.
 *      - ISDOTDOT:     Must be set if and only if cn_nameptr == ".."
 * - tsp:       Return storage for cache timestamp.  On a successful (positive
 *              or negative) lookup, tsp will be filled with any timespec that
 *              was stored when this cache entry was created.  However, it will
 *              be clear for "." entries.
 * - ticks:     Return storage for alternate cache timestamp.  On a successful
 *              (positive or negative) lookup, it will contain the ticks value
 *              that was current when the cache entry was created, unless cnp
 *              was ".".
 *
 * # Returns
 *
 * - -1:        A positive cache hit.  vpp will contain the desired vnode.
 * - ENOENT:    A negative cache hit, or dvp was recycled out from under us due
 *              to a forced unmount.  vpp will not be modified.  If the entry
 *              is a whiteout, then the ISWHITEOUT flag will be set in
 *              cnp->cn_flags.
 * - 0:         A cache miss.  vpp will not be modified.
 *
 * # Locking
 *
 * On a cache hit, vpp will be returned locked and ref'd.  If we're looking up
 * .., dvp is unlocked.  If we're looking up . an extra ref is taken, but the
 * lock is not recursively acquired.
 */
int
cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp,
    struct timespec *tsp, int *ticksp)
{
        struct namecache_ts *ncp_ts;
        struct namecache *ncp;
        struct rwlock *blp;
        struct mtx *dvlp;
        uint32_t hash;
        enum vgetstate vs;
        int error, ltype;

#ifdef DEBUG_CACHE
        if (__predict_false(!doingcache)) {
                cnp->cn_flags &= ~MAKEENTRY;
                return (0);
        }
#endif

        counter_u64_add(numcalls, 1);

        if (__predict_false(cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.'))
                return (cache_lookup_dot(dvp, vpp, cnp, tsp, ticksp));

        if ((cnp->cn_flags & MAKEENTRY) == 0)
                return (cache_lookup_nomakeentry(dvp, vpp, cnp, tsp, ticksp));

retry:
        blp = NULL;
        dvlp = NULL;
        error = 0;
        if (cnp->cn_namelen == 2 &&
            cnp->cn_nameptr[0] == '.' && cnp->cn_nameptr[1] == '.') {
                counter_u64_add(dotdothits, 1);
                dvlp = VP2VNODELOCK(dvp);
                mtx_lock(dvlp);
                ncp = dvp->v_cache_dd;
                if (ncp == NULL) {
                        SDT_PROBE3(vfs, namecache, lookup, miss, dvp,
                            "..", NULL);
                        mtx_unlock(dvlp);
                        return (0);
                }
                if ((ncp->nc_flag & NCF_ISDOTDOT) != 0) {
                        if (ncp->nc_flag & NCF_NEGATIVE)
                                *vpp = NULL;
                        else
                                *vpp = ncp->nc_vp;
                } else
                        *vpp = ncp->nc_dvp;
                /* Return failure if negative entry was found. */
                if (*vpp == NULL)
                        goto negative_success;
                CTR3(KTR_VFS, "cache_lookup(%p, %s) found %p via ..",
                    dvp, cnp->cn_nameptr, *vpp);
                SDT_PROBE3(vfs, namecache, lookup, hit, dvp, "..",
                    *vpp);
                cache_out_ts(ncp, tsp, ticksp);
                if ((ncp->nc_flag & (NCF_ISDOTDOT | NCF_DTS)) ==
                    NCF_DTS && tsp != NULL) {
                        ncp_ts = __containerof(ncp, struct namecache_ts, nc_nc);
                        *tsp = ncp_ts->nc_dotdottime;
                }
                goto success;
        }

        hash = cache_get_hash(cnp->cn_nameptr, cnp->cn_namelen, dvp);
        blp = HASH2BUCKETLOCK(hash);
        rw_rlock(blp);

        LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
                counter_u64_add(numchecks, 1);
                if (ncp->nc_dvp == dvp && ncp->nc_nlen == cnp->cn_namelen &&
                    !bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen))
                        break;
        }

        /* We failed to find an entry */
        if (__predict_false(ncp == NULL)) {
                rw_runlock(blp);
                SDT_PROBE3(vfs, namecache, lookup, miss, dvp, cnp->cn_nameptr,
                    NULL);
                counter_u64_add(nummiss, 1);
                return (0);
        }

        if (ncp->nc_flag & NCF_NEGATIVE)
                goto negative_success;

        /* We found a "positive" match, return the vnode */
        counter_u64_add(numposhits, 1);
        *vpp = ncp->nc_vp;
        CTR4(KTR_VFS, "cache_lookup(%p, %s) found %p via ncp %p",
            dvp, cnp->cn_nameptr, *vpp, ncp);
        SDT_PROBE3(vfs, namecache, lookup, hit, dvp, ncp->nc_name,
            *vpp);
        cache_out_ts(ncp, tsp, ticksp);
success:
        /*
         * On success we return a locked and ref'd vnode as per the lookup
         * protocol.
         */
        MPASS(dvp != *vpp);
        ltype = 0;      /* silence gcc warning */
        if (cnp->cn_flags & ISDOTDOT) {
                ltype = VOP_ISLOCKED(dvp);
                VOP_UNLOCK(dvp);
        }
        vs = vget_prep(*vpp);
        cache_lookup_unlock(blp, dvlp);
        error = vget_finish(*vpp, cnp->cn_lkflags, vs);
        if (cnp->cn_flags & ISDOTDOT) {
                vn_lock(dvp, ltype | LK_RETRY);
                if (VN_IS_DOOMED(dvp)) {
                        if (error == 0)
                                vput(*vpp);
                        *vpp = NULL;
                        return (ENOENT);
                }
        }
        if (error) {
                *vpp = NULL;
                goto retry;
        }
        if ((cnp->cn_flags & ISLASTCN) &&
            (cnp->cn_lkflags & LK_TYPE_MASK) == LK_EXCLUSIVE) {
                ASSERT_VOP_ELOCKED(*vpp, "cache_lookup");
        }
        return (-1);

negative_success:
        /* We found a negative match, and want to create it, so purge */
        if (cnp->cn_nameiop == CREATE) {
                counter_u64_add(numnegzaps, 1);
                goto zap_and_exit;
        }

        counter_u64_add(numneghits, 1);
        cache_negative_hit(ncp);
        if (ncp->nc_flag & NCF_WHITE)
                cnp->cn_flags |= ISWHITEOUT;
        SDT_PROBE2(vfs, namecache, lookup, hit__negative, dvp,
            ncp->nc_name);
        cache_out_ts(ncp, tsp, ticksp);
        cache_lookup_unlock(blp, dvlp);
        return (ENOENT);

zap_and_exit:
        if (blp != NULL)
                error = cache_zap_rlocked_bucket(ncp, cnp, hash, blp);
        else
                error = cache_zap_locked_vnode(ncp, dvp);
        if (__predict_false(error != 0)) {
                zap_and_exit_bucket_fail2++;
                cache_maybe_yield();
                goto retry;
        }
        cache_free(ncp);
        return (0);
}

struct celockstate {
        struct mtx *vlp[3];
        struct rwlock *blp[2];
};
CTASSERT((nitems(((struct celockstate *)0)->vlp) == 3));
CTASSERT((nitems(((struct celockstate *)0)->blp) == 2));

static inline void
cache_celockstate_init(struct celockstate *cel)
{

        bzero(cel, sizeof(*cel));
}

static void
cache_lock_vnodes_cel(struct celockstate *cel, struct vnode *vp,
    struct vnode *dvp)
{
        struct mtx *vlp1, *vlp2;

        MPASS(cel->vlp[0] == NULL);
        MPASS(cel->vlp[1] == NULL);
        MPASS(cel->vlp[2] == NULL);

        MPASS(vp != NULL || dvp != NULL);

        vlp1 = VP2VNODELOCK(vp);
        vlp2 = VP2VNODELOCK(dvp);
        cache_sort_vnodes(&vlp1, &vlp2);

        if (vlp1 != NULL) {
                mtx_lock(vlp1);
                cel->vlp[0] = vlp1;
        }
        mtx_lock(vlp2);
        cel->vlp[1] = vlp2;
}

static void
cache_unlock_vnodes_cel(struct celockstate *cel)
{

        MPASS(cel->vlp[0] != NULL || cel->vlp[1] != NULL);

        if (cel->vlp[0] != NULL)
                mtx_unlock(cel->vlp[0]);
        if (cel->vlp[1] != NULL)
                mtx_unlock(cel->vlp[1]);
        if (cel->vlp[2] != NULL)
                mtx_unlock(cel->vlp[2]);
}

static bool
cache_lock_vnodes_cel_3(struct celockstate *cel, struct vnode *vp)
{
        struct mtx *vlp;
        bool ret;

        cache_assert_vlp_locked(cel->vlp[0]);
        cache_assert_vlp_locked(cel->vlp[1]);
        MPASS(cel->vlp[2] == NULL);

        MPASS(vp != NULL);
        vlp = VP2VNODELOCK(vp);

        ret = true;
        if (vlp >= cel->vlp[1]) {
                mtx_lock(vlp);
        } else {
                if (mtx_trylock(vlp))
                        goto out;
                cache_lock_vnodes_cel_3_failures++;
                cache_unlock_vnodes_cel(cel);
                if (vlp < cel->vlp[0]) {
                        mtx_lock(vlp);
                        mtx_lock(cel->vlp[0]);
                        mtx_lock(cel->vlp[1]);
                } else {
                        if (cel->vlp[0] != NULL)
                                mtx_lock(cel->vlp[0]);
                        mtx_lock(vlp);
                        mtx_lock(cel->vlp[1]);
                }
                ret = false;
        }
out:
        cel->vlp[2] = vlp;
        return (ret);
}

static void
cache_lock_buckets_cel(struct celockstate *cel, struct rwlock *blp1,
    struct rwlock *blp2)
{

        MPASS(cel->blp[0] == NULL);
        MPASS(cel->blp[1] == NULL);

        cache_sort_vnodes(&blp1, &blp2);

        if (blp1 != NULL) {
                rw_wlock(blp1);
                cel->blp[0] = blp1;
        }
        rw_wlock(blp2);
        cel->blp[1] = blp2;
}

static void
cache_unlock_buckets_cel(struct celockstate *cel)
{

        if (cel->blp[0] != NULL)
                rw_wunlock(cel->blp[0]);
        rw_wunlock(cel->blp[1]);
}

/*
 * Lock part of the cache affected by the insertion.
 *
 * This means vnodelocks for dvp, vp and the relevant bucketlock.
 * However, insertion can result in removal of an old entry. In this
 * case we have an additional vnode and bucketlock pair to lock. If the
 * entry is negative, ncelock is locked instead of the vnode.
 *
 * That is, in the worst case we have to lock 3 vnodes and 2 bucketlocks, while
 * preserving the locking order (smaller address first).
 */
static void
cache_enter_lock(struct celockstate *cel, struct vnode *dvp, struct vnode *vp,
    uint32_t hash)
{
        struct namecache *ncp;
        struct rwlock *blps[2];

        blps[0] = HASH2BUCKETLOCK(hash);
        for (;;) {
                blps[1] = NULL;
                cache_lock_vnodes_cel(cel, dvp, vp);
                if (vp == NULL || vp->v_type != VDIR)
                        break;
                ncp = vp->v_cache_dd;
                if (ncp == NULL)
                        break;
                if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
                        break;
                MPASS(ncp->nc_dvp == vp);
                blps[1] = NCP2BUCKETLOCK(ncp);
                if (ncp->nc_flag & NCF_NEGATIVE)
                        break;
                if (cache_lock_vnodes_cel_3(cel, ncp->nc_vp))
                        break;
                /*
                 * All vnodes got re-locked. Re-validate the state and if
                 * nothing changed we are done. Otherwise restart.
                 */
                if (ncp == vp->v_cache_dd &&
                    (ncp->nc_flag & NCF_ISDOTDOT) != 0 &&
                    blps[1] == NCP2BUCKETLOCK(ncp) &&
                    VP2VNODELOCK(ncp->nc_vp) == cel->vlp[2])
                        break;
                cache_unlock_vnodes_cel(cel);
                cel->vlp[0] = NULL;
                cel->vlp[1] = NULL;
                cel->vlp[2] = NULL;
        }
        cache_lock_buckets_cel(cel, blps[0], blps[1]);
}

static void
cache_enter_lock_dd(struct celockstate *cel, struct vnode *dvp, struct vnode *vp,
    uint32_t hash)
{
        struct namecache *ncp;
        struct rwlock *blps[2];

        blps[0] = HASH2BUCKETLOCK(hash);
        for (;;) {
                blps[1] = NULL;
                cache_lock_vnodes_cel(cel, dvp, vp);
                ncp = dvp->v_cache_dd;
                if (ncp == NULL)
                        break;
                if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
                        break;
                MPASS(ncp->nc_dvp == dvp);
                blps[1] = NCP2BUCKETLOCK(ncp);
                if (ncp->nc_flag & NCF_NEGATIVE)
                        break;
                if (cache_lock_vnodes_cel_3(cel, ncp->nc_vp))
                        break;
                if (ncp == dvp->v_cache_dd &&
                    (ncp->nc_flag & NCF_ISDOTDOT) != 0 &&
                    blps[1] == NCP2BUCKETLOCK(ncp) &&
                    VP2VNODELOCK(ncp->nc_vp) == cel->vlp[2])
                        break;
                cache_unlock_vnodes_cel(cel);
                cel->vlp[0] = NULL;
                cel->vlp[1] = NULL;
                cel->vlp[2] = NULL;
        }
        cache_lock_buckets_cel(cel, blps[0], blps[1]);
}

static void
cache_enter_unlock(struct celockstate *cel)
{

        cache_unlock_buckets_cel(cel);
        cache_unlock_vnodes_cel(cel);
}

static void __noinline
cache_enter_dotdot_prep(struct vnode *dvp, struct vnode *vp,
    struct componentname *cnp)
{
        struct celockstate cel;
        struct namecache *ncp;
        uint32_t hash;
        int len;

        if (dvp->v_cache_dd == NULL)
                return;
        len = cnp->cn_namelen;
        cache_celockstate_init(&cel);
        hash = cache_get_hash(cnp->cn_nameptr, len, dvp);
        cache_enter_lock_dd(&cel, dvp, vp, hash);
        ncp = dvp->v_cache_dd;
        if (ncp != NULL && (ncp->nc_flag & NCF_ISDOTDOT)) {
                KASSERT(ncp->nc_dvp == dvp, ("wrong isdotdot parent"));
                cache_zap_locked(ncp, false);
        } else {
                ncp = NULL;
        }
        dvp->v_cache_dd = NULL;
        cache_enter_unlock(&cel);
        cache_free(ncp);
}

/*
 * Add an entry to the cache.
 */
void
cache_enter_time(struct vnode *dvp, struct vnode *vp, struct componentname *cnp,
    struct timespec *tsp, struct timespec *dtsp)
{
        struct celockstate cel;
        struct namecache *ncp, *n2, *ndd;
        struct namecache_ts *ncp_ts, *n2_ts;
        struct nchashhead *ncpp;
        uint32_t hash;
        int flag;
        int len;
        u_long lnumcache;

        CTR3(KTR_VFS, "cache_enter(%p, %p, %s)", dvp, vp, cnp->cn_nameptr);
        VNASSERT(vp == NULL || !VN_IS_DOOMED(vp), vp,
            ("cache_enter: Adding a doomed vnode"));
        VNASSERT(dvp == NULL || !VN_IS_DOOMED(dvp), dvp,
            ("cache_enter: Doomed vnode used as src"));

#ifdef DEBUG_CACHE
        if (__predict_false(!doingcache))
                return;
#endif

        flag = 0;
        if (__predict_false(cnp->cn_nameptr[0] == '.')) {
                if (cnp->cn_namelen == 1)
                        return;
                if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
                        cache_enter_dotdot_prep(dvp, vp, cnp);
                        flag = NCF_ISDOTDOT;
                }
        }

        /*
         * Avoid blowout in namecache entries.
         */
        lnumcache = atomic_fetchadd_long(&numcache, 1) + 1;
        if (__predict_false(lnumcache >= ncsize)) {
                atomic_add_long(&numcache, -1);
                return;
        }

        cache_celockstate_init(&cel);
        ndd = NULL;
        ncp_ts = NULL;

        /*
         * Calculate the hash key and setup as much of the new
         * namecache entry as possible before acquiring the lock.
         */
        ncp = cache_alloc(cnp->cn_namelen, tsp != NULL);
        ncp->nc_flag = flag;
        ncp->nc_vp = vp;
        if (vp == NULL)
                ncp->nc_flag |= NCF_NEGATIVE;
        ncp->nc_dvp = dvp;
        if (tsp != NULL) {
                ncp_ts = __containerof(ncp, struct namecache_ts, nc_nc);
                ncp_ts->nc_time = *tsp;
                ncp_ts->nc_ticks = ticks;
                ncp_ts->nc_nc.nc_flag |= NCF_TS;
                if (dtsp != NULL) {
                        ncp_ts->nc_dotdottime = *dtsp;
                        ncp_ts->nc_nc.nc_flag |= NCF_DTS;
                }
        }
        len = ncp->nc_nlen = cnp->cn_namelen;
        hash = cache_get_hash(cnp->cn_nameptr, len, dvp);
        strlcpy(ncp->nc_name, cnp->cn_nameptr, len + 1);
        cache_enter_lock(&cel, dvp, vp, hash);

        /*
         * See if this vnode or negative entry is already in the cache
         * with this name.  This can happen with concurrent lookups of
         * the same path name.
         */
        ncpp = NCHHASH(hash);
        LIST_FOREACH(n2, ncpp, nc_hash) {
                if (n2->nc_dvp == dvp &&
                    n2->nc_nlen == cnp->cn_namelen &&
                    !bcmp(n2->nc_name, cnp->cn_nameptr, n2->nc_nlen)) {
                        if (tsp != NULL) {
                                KASSERT((n2->nc_flag & NCF_TS) != 0,
                                    ("no NCF_TS"));
                                n2_ts = __containerof(n2, struct namecache_ts, nc_nc);
                                n2_ts->nc_time = ncp_ts->nc_time;
                                n2_ts->nc_ticks = ncp_ts->nc_ticks;
                                if (dtsp != NULL) {
                                        n2_ts->nc_dotdottime = ncp_ts->nc_dotdottime;
                                        if (ncp->nc_flag & NCF_NEGATIVE)
                                                mtx_lock(&ncneg_hot.nl_lock);
                                        n2_ts->nc_nc.nc_flag |= NCF_DTS;
                                        if (ncp->nc_flag & NCF_NEGATIVE)
                                                mtx_unlock(&ncneg_hot.nl_lock);
                                }
                        }
                        goto out_unlock_free;
                }
        }

        if (flag == NCF_ISDOTDOT) {
                /*
                 * See if we are trying to add .. entry, but some other lookup
                 * has populated v_cache_dd pointer already.
                 */
                if (dvp->v_cache_dd != NULL)
                        goto out_unlock_free;
                KASSERT(vp == NULL || vp->v_type == VDIR,
                    ("wrong vnode type %p", vp));
                dvp->v_cache_dd = ncp;
        }

        if (vp != NULL) {
                if (vp->v_type == VDIR) {
                        if (flag != NCF_ISDOTDOT) {
                                /*
                                 * For this case, the cache entry maps both the
                                 * directory name in it and the name ".." for the
                                 * directory's parent.
                                 */
                                if ((ndd = vp->v_cache_dd) != NULL) {
                                        if ((ndd->nc_flag & NCF_ISDOTDOT) != 0)
                                                cache_zap_locked(ndd, false);
                                        else
                                                ndd = NULL;
                                }
                                vp->v_cache_dd = ncp;
                        }
                } else {
                        vp->v_cache_dd = NULL;
                }
        }

        if (flag != NCF_ISDOTDOT) {
                if (LIST_EMPTY(&dvp->v_cache_src)) {
                        vhold(dvp);
                        counter_u64_add(numcachehv, 1);
                }
                LIST_INSERT_HEAD(&dvp->v_cache_src, ncp, nc_src);
        }

        /*
         * Insert the new namecache entry into the appropriate chain
         * within the cache entries table.
         */
        LIST_INSERT_HEAD(ncpp, ncp, nc_hash);

        /*
         * If the entry is "negative", we place it into the
         * "negative" cache queue, otherwise, we place it into the
         * destination vnode's cache entries queue.
         */
        if (vp != NULL) {
                TAILQ_INSERT_HEAD(&vp->v_cache_dst, ncp, nc_dst);
                SDT_PROBE3(vfs, namecache, enter, done, dvp, ncp->nc_name,
                    vp);
        } else {
                if (cnp->cn_flags & ISWHITEOUT)
                        ncp->nc_flag |= NCF_WHITE;
                cache_negative_insert(ncp, false);
                SDT_PROBE2(vfs, namecache, enter_negative, done, dvp,
                    ncp->nc_name);
        }
        cache_enter_unlock(&cel);
        if (numneg * ncnegfactor > lnumcache)
                cache_negative_zap_one();
        cache_free(ndd);
        return;
out_unlock_free:
        cache_enter_unlock(&cel);
        cache_free(ncp);
        return;
}

static u_int
cache_roundup_2(u_int val)
{
        u_int res;

        for (res = 1; res <= val; res <<= 1)
                continue;

        return (res);
}

/*
 * Name cache initialization, from vfs_init() when we are booting
 */
static void
nchinit(void *dummy __unused)
{
        u_int i;

        cache_zone_small = uma_zcreate("S VFS Cache",
            sizeof(struct namecache) + CACHE_PATH_CUTOFF + 1,
            NULL, NULL, NULL, NULL, UMA_ALIGNOF(struct namecache),
            UMA_ZONE_ZINIT);
        cache_zone_small_ts = uma_zcreate("STS VFS Cache",
            sizeof(struct namecache_ts) + CACHE_PATH_CUTOFF + 1,
            NULL, NULL, NULL, NULL, UMA_ALIGNOF(struct namecache_ts),
            UMA_ZONE_ZINIT);
        cache_zone_large = uma_zcreate("L VFS Cache",
            sizeof(struct namecache) + NAME_MAX + 1,
            NULL, NULL, NULL, NULL, UMA_ALIGNOF(struct namecache),
            UMA_ZONE_ZINIT);
        cache_zone_large_ts = uma_zcreate("LTS VFS Cache",
            sizeof(struct namecache_ts) + NAME_MAX + 1,
            NULL, NULL, NULL, NULL, UMA_ALIGNOF(struct namecache_ts),
            UMA_ZONE_ZINIT);

        ncsize = desiredvnodes * ncsizefactor;
        nchashtbl = hashinit(desiredvnodes * 2, M_VFSCACHE, &nchash);
        ncbuckethash = cache_roundup_2(mp_ncpus * mp_ncpus) - 1;
        if (ncbuckethash < 7) /* arbitrarily chosen to avoid having one lock */
                ncbuckethash = 7;
        if (ncbuckethash > nchash)
                ncbuckethash = nchash;
        bucketlocks = malloc(sizeof(*bucketlocks) * numbucketlocks, M_VFSCACHE,
            M_WAITOK | M_ZERO);
        for (i = 0; i < numbucketlocks; i++)
                rw_init_flags(&bucketlocks[i], "ncbuc", RW_DUPOK | RW_RECURSE);
        ncvnodehash = ncbuckethash;
        vnodelocks = malloc(sizeof(*vnodelocks) * numvnodelocks, M_VFSCACHE,
            M_WAITOK | M_ZERO);
        for (i = 0; i < numvnodelocks; i++)
                mtx_init(&vnodelocks[i], "ncvn", NULL, MTX_DUPOK | MTX_RECURSE);
        ncpurgeminvnodes = numbucketlocks * 2;

        ncneghash = 3;
        neglists = malloc(sizeof(*neglists) * numneglists, M_VFSCACHE,
            M_WAITOK | M_ZERO);
        for (i = 0; i < numneglists; i++) {
                mtx_init(&neglists[i].nl_lock, "ncnegl", NULL, MTX_DEF);
                TAILQ_INIT(&neglists[i].nl_list);
        }
        mtx_init(&ncneg_hot.nl_lock, "ncneglh", NULL, MTX_DEF);
        TAILQ_INIT(&ncneg_hot.nl_list);

        mtx_init(&ncneg_shrink_lock, "ncnegs", NULL, MTX_DEF);

        numcachehv = counter_u64_alloc(M_WAITOK);
        numcalls = counter_u64_alloc(M_WAITOK);
        dothits = counter_u64_alloc(M_WAITOK);
        dotdothits = counter_u64_alloc(M_WAITOK);
        numchecks = counter_u64_alloc(M_WAITOK);
        nummiss = counter_u64_alloc(M_WAITOK);
        nummisszap = counter_u64_alloc(M_WAITOK);
        numposzaps = counter_u64_alloc(M_WAITOK);
        numposhits = counter_u64_alloc(M_WAITOK);
        numnegzaps = counter_u64_alloc(M_WAITOK);
        numneghits = counter_u64_alloc(M_WAITOK);
        numfullpathcalls = counter_u64_alloc(M_WAITOK);
        numfullpathfail1 = counter_u64_alloc(M_WAITOK);
        numfullpathfail2 = counter_u64_alloc(M_WAITOK);
        numfullpathfail4 = counter_u64_alloc(M_WAITOK);
        numfullpathfound = counter_u64_alloc(M_WAITOK);
        zap_and_exit_bucket_relock_success = counter_u64_alloc(M_WAITOK);
        numneg_evicted = counter_u64_alloc(M_WAITOK);
        shrinking_skipped = counter_u64_alloc(M_WAITOK);
}
SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nchinit, NULL);

void
cache_changesize(u_long newmaxvnodes)
{
        struct nchashhead *new_nchashtbl, *old_nchashtbl;
        u_long new_nchash, old_nchash;
        struct namecache *ncp;
        uint32_t hash;
        u_long newncsize;
        int i;

        newncsize = newmaxvnodes * ncsizefactor;
        newmaxvnodes = cache_roundup_2(newmaxvnodes * 2);
        if (newmaxvnodes < numbucketlocks)
                newmaxvnodes = numbucketlocks;

        new_nchashtbl = hashinit(newmaxvnodes, M_VFSCACHE, &new_nchash);
        /* If same hash table size, nothing to do */
        if (nchash == new_nchash) {
                free(new_nchashtbl, M_VFSCACHE);
                return;
        }
        /*
         * Move everything from the old hash table to the new table.
         * None of the namecache entries in the table can be removed
         * because to do so, they have to be removed from the hash table.
         */
        cache_lock_all_vnodes();
        cache_lock_all_buckets();
        old_nchashtbl = nchashtbl;
        old_nchash = nchash;
        nchashtbl = new_nchashtbl;
        nchash = new_nchash;
        for (i = 0; i <= old_nchash; i++) {
                while ((ncp = LIST_FIRST(&old_nchashtbl[i])) != NULL) {
                        hash = cache_get_hash(ncp->nc_name, ncp->nc_nlen,
                            ncp->nc_dvp);
                        LIST_REMOVE(ncp, nc_hash);
                        LIST_INSERT_HEAD(NCHHASH(hash), ncp, nc_hash);
                }
        }
        ncsize = newncsize;
        cache_unlock_all_buckets();
        cache_unlock_all_vnodes();
        free(old_nchashtbl, M_VFSCACHE);
}

/*
 * Invalidate all entries from and to a particular vnode.
 */
void
cache_purge(struct vnode *vp)
{
        TAILQ_HEAD(, namecache) ncps;
        struct namecache *ncp, *nnp;
        struct mtx *vlp, *vlp2;

        CTR1(KTR_VFS, "cache_purge(%p)", vp);
        SDT_PROBE1(vfs, namecache, purge, done, vp);
        if (LIST_EMPTY(&vp->v_cache_src) && TAILQ_EMPTY(&vp->v_cache_dst) &&
            vp->v_cache_dd == NULL)
                return;
        TAILQ_INIT(&ncps);
        vlp = VP2VNODELOCK(vp);
        vlp2 = NULL;
        mtx_lock(vlp);
retry:
        while (!LIST_EMPTY(&vp->v_cache_src)) {
                ncp = LIST_FIRST(&vp->v_cache_src);
                if (!cache_zap_locked_vnode_kl2(ncp, vp, &vlp2))
                        goto retry;
                TAILQ_INSERT_TAIL(&ncps, ncp, nc_dst);
        }
        while (!TAILQ_EMPTY(&vp->v_cache_dst)) {
                ncp = TAILQ_FIRST(&vp->v_cache_dst);
                if (!cache_zap_locked_vnode_kl2(ncp, vp, &vlp2))
                        goto retry;
                TAILQ_INSERT_TAIL(&ncps, ncp, nc_dst);
        }
        ncp = vp->v_cache_dd;
        if (ncp != NULL) {
                KASSERT(ncp->nc_flag & NCF_ISDOTDOT,
                   ("lost dotdot link"));
                if (!cache_zap_locked_vnode_kl2(ncp, vp, &vlp2))
                        goto retry;
                TAILQ_INSERT_TAIL(&ncps, ncp, nc_dst);
        }
        KASSERT(vp->v_cache_dd == NULL, ("incomplete purge"));
        mtx_unlock(vlp);
        if (vlp2 != NULL)
                mtx_unlock(vlp2);
        TAILQ_FOREACH_SAFE(ncp, &ncps, nc_dst, nnp) {
                cache_free(ncp);
        }
}

/*
 * Invalidate all negative entries for a particular directory vnode.
 */
void
cache_purge_negative(struct vnode *vp)
{
        TAILQ_HEAD(, namecache) ncps;
        struct namecache *ncp, *nnp;
        struct mtx *vlp;

        CTR1(KTR_VFS, "cache_purge_negative(%p)", vp);
        SDT_PROBE1(vfs, namecache, purge_negative, done, vp);
        if (LIST_EMPTY(&vp->v_cache_src))
                return;
        TAILQ_INIT(&ncps);
        vlp = VP2VNODELOCK(vp);
        mtx_lock(vlp);
        LIST_FOREACH_SAFE(ncp, &vp->v_cache_src, nc_src, nnp) {
                if (!(ncp->nc_flag & NCF_NEGATIVE))
                        continue;
                cache_zap_negative_locked_vnode_kl(ncp, vp);
                TAILQ_INSERT_TAIL(&ncps, ncp, nc_dst);
        }
        mtx_unlock(vlp);
        TAILQ_FOREACH_SAFE(ncp, &ncps, nc_dst, nnp) {
                cache_free(ncp);
        }
}

/*
 * Flush all entries referencing a particular filesystem.
 */
void
cache_purgevfs(struct mount *mp, bool force)
{
        TAILQ_HEAD(, namecache) ncps;
        struct mtx *vlp1, *vlp2;
        struct rwlock *blp;
        struct nchashhead *bucket;
        struct namecache *ncp, *nnp;
        u_long i, j, n_nchash;
        int error;

        /* Scan hash tables for applicable entries */
        SDT_PROBE1(vfs, namecache, purgevfs, done, mp);
        if (!force && mp->mnt_nvnodelistsize <= ncpurgeminvnodes)
                return;
        TAILQ_INIT(&ncps);
        n_nchash = nchash + 1;
        vlp1 = vlp2 = NULL;
        for (i = 0; i < numbucketlocks; i++) {
                blp = (struct rwlock *)&bucketlocks[i];
                rw_wlock(blp);
                for (j = i; j < n_nchash; j += numbucketlocks) {
retry:
                        bucket = &nchashtbl[j];
                        LIST_FOREACH_SAFE(ncp, bucket, nc_hash, nnp) {
                                cache_assert_bucket_locked(ncp, RA_WLOCKED);
                                if (ncp->nc_dvp->v_mount != mp)
                                        continue;
                                error = cache_zap_wlocked_bucket_kl(ncp, blp,
                                    &vlp1, &vlp2);
                                if (error != 0)
                                        goto retry;
                                TAILQ_INSERT_HEAD(&ncps, ncp, nc_dst);
                        }
                }
                rw_wunlock(blp);
                if (vlp1 == NULL && vlp2 == NULL)
                        cache_maybe_yield();
        }
        if (vlp1 != NULL)
                mtx_unlock(vlp1);
        if (vlp2 != NULL)
                mtx_unlock(vlp2);

        TAILQ_FOREACH_SAFE(ncp, &ncps, nc_dst, nnp) {
                cache_free(ncp);
        }
}

/*
 * Perform canonical checks and cache lookup and pass on to filesystem
 * through the vop_cachedlookup only if needed.
 */

int
vfs_cache_lookup(struct vop_lookup_args *ap)
{
        struct vnode *dvp;
        int error;
        struct vnode **vpp = ap->a_vpp;
        struct componentname *cnp = ap->a_cnp;
        struct ucred *cred = cnp->cn_cred;
        int flags = cnp->cn_flags;
        struct thread *td = cnp->cn_thread;

        *vpp = NULL;
        dvp = ap->a_dvp;

        if (dvp->v_type != VDIR)
                return (ENOTDIR);

        if ((flags & ISLASTCN) && (dvp->v_mount->mnt_flag & MNT_RDONLY) &&
            (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME))
                return (EROFS);

        error = VOP_ACCESS(dvp, VEXEC, cred, td);
        if (error)
                return (error);

        error = cache_lookup(dvp, vpp, cnp, NULL, NULL);
        if (error == 0)
                return (VOP_CACHEDLOOKUP(dvp, vpp, cnp));
        if (error == -1)
                return (0);
        return (error);
}

/* Implementation of the getcwd syscall. */
int
sys___getcwd(struct thread *td, struct __getcwd_args *uap)
{

        return (kern___getcwd(td, uap->buf, UIO_USERSPACE, uap->buflen,
            MAXPATHLEN));
}

int
kern___getcwd(struct thread *td, char *buf, enum uio_seg bufseg, size_t buflen,
    size_t path_max)
{
        char *bp, *tmpbuf;
        struct filedesc *fdp;
        struct vnode *cdir, *rdir;
        int error;

        if (__predict_false(buflen < 2))
                return (EINVAL);
        if (buflen > path_max)
                buflen = path_max;

        tmpbuf = malloc(buflen, M_TEMP, M_WAITOK);
        fdp = td->td_proc->p_fd;
        FILEDESC_SLOCK(fdp);
        cdir = fdp->fd_cdir;
        vrefact(cdir);
        rdir = fdp->fd_rdir;
        vrefact(rdir);
        FILEDESC_SUNLOCK(fdp);
        error = vn_fullpath1(td, cdir, rdir, tmpbuf, &bp, buflen);
        vrele(rdir);
        vrele(cdir);

        if (!error) {
                if (bufseg == UIO_SYSSPACE)
                        bcopy(bp, buf, strlen(bp) + 1);
                else
                        error = copyout(bp, buf, strlen(bp) + 1);
#ifdef KTRACE
        if (KTRPOINT(curthread, KTR_NAMEI))
                ktrnamei(bp);
#endif
        }
        free(tmpbuf, M_TEMP);
        return (error);
}

/*
 * Retrieve the full filesystem path that correspond to a vnode from the name
 * cache (if available)
 */
int
vn_fullpath(struct thread *td, struct vnode *vn, char **retbuf, char **freebuf)
{
        char *buf;
        struct filedesc *fdp;
        struct vnode *rdir;
        int error;

        if (__predict_false(vn == NULL))
                return (EINVAL);

        buf = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
        fdp = td->td_proc->p_fd;
        FILEDESC_SLOCK(fdp);
        rdir = fdp->fd_rdir;
        vrefact(rdir);
        FILEDESC_SUNLOCK(fdp);
        error = vn_fullpath1(td, vn, rdir, buf, retbuf, MAXPATHLEN);
        vrele(rdir);

        if (!error)
                *freebuf = buf;
        else
                free(buf, M_TEMP);
        return (error);
}

/*
 * This function is similar to vn_fullpath, but it attempts to lookup the
 * pathname relative to the global root mount point.  This is required for the
 * auditing sub-system, as audited pathnames must be absolute, relative to the
 * global root mount point.
 */
int
vn_fullpath_global(struct thread *td, struct vnode *vn,
    char **retbuf, char **freebuf)
{
        char *buf;
        int error;

        if (__predict_false(vn == NULL))
                return (EINVAL);
        buf = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
        error = vn_fullpath1(td, vn, rootvnode, buf, retbuf, MAXPATHLEN);
        if (!error)
                *freebuf = buf;
        else
                free(buf, M_TEMP);
        return (error);
}

int
vn_vptocnp(struct vnode **vp, struct ucred *cred, char *buf, size_t *buflen)
{
        struct vnode *dvp;
        struct namecache *ncp;
        struct mtx *vlp;
        int error;

        vlp = VP2VNODELOCK(*vp);
        mtx_lock(vlp);
        TAILQ_FOREACH(ncp, &((*vp)->v_cache_dst), nc_dst) {
                if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
                        break;
        }
        if (ncp != NULL) {
                if (*buflen < ncp->nc_nlen) {
                        mtx_unlock(vlp);
                        vrele(*vp);
                        counter_u64_add(numfullpathfail4, 1);
                        error = ENOMEM;
                        SDT_PROBE3(vfs, namecache, fullpath, return, error,
                            vp, NULL);
                        return (error);
                }
                *buflen -= ncp->nc_nlen;
                memcpy(buf + *buflen, ncp->nc_name, ncp->nc_nlen);
                SDT_PROBE3(vfs, namecache, fullpath, hit, ncp->nc_dvp,
                    ncp->nc_name, vp);
                dvp = *vp;
                *vp = ncp->nc_dvp;
                vref(*vp);
                mtx_unlock(vlp);
                vrele(dvp);
                return (0);
        }
        SDT_PROBE1(vfs, namecache, fullpath, miss, vp);

        mtx_unlock(vlp);
        vn_lock(*vp, LK_SHARED | LK_RETRY);
        error = VOP_VPTOCNP(*vp, &dvp, cred, buf, buflen);
        vput(*vp);
        if (error) {
                counter_u64_add(numfullpathfail2, 1);
                SDT_PROBE3(vfs, namecache, fullpath, return,  error, vp, NULL);
                return (error);
        }

        *vp = dvp;
        if (VN_IS_DOOMED(dvp)) {
                /* forced unmount */
                vrele(dvp);
                error = ENOENT;
                SDT_PROBE3(vfs, namecache, fullpath, return, error, vp, NULL);
                return (error);
        }
        /*
         * *vp has its use count incremented still.
         */

        return (0);
}

/*
 * The magic behind kern___getcwd() and vn_fullpath().
 */
static int
vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
    char *buf, char **retbuf, size_t buflen)
{
        int error, slash_prefixed;
#ifdef KDTRACE_HOOKS
        struct vnode *startvp = vp;
#endif
        struct vnode *vp1;

        buflen--;
        buf[buflen] = '\0';
        error = 0;
        slash_prefixed = 0;

        SDT_PROBE1(vfs, namecache, fullpath, entry, vp);
        counter_u64_add(numfullpathcalls, 1);
        vref(vp);
        if (vp->v_type != VDIR) {
                error = vn_vptocnp(&vp, td->td_ucred, buf, &buflen);
                if (error)
                        return (error);
                if (buflen == 0) {
                        vrele(vp);
                        return (ENOMEM);
                }
                buf[--buflen] = '/';
                slash_prefixed = 1;
        }
        while (vp != rdir && vp != rootvnode) {
                /*
                 * The vp vnode must be already fully constructed,
                 * since it is either found in namecache or obtained
                 * from VOP_VPTOCNP().  We may test for VV_ROOT safely
                 * without obtaining the vnode lock.
                 */
                if ((vp->v_vflag & VV_ROOT) != 0) {
                        vn_lock(vp, LK_RETRY | LK_SHARED);

                        /*
                         * With the vnode locked, check for races with
                         * unmount, forced or not.  Note that we
                         * already verified that vp is not equal to
                         * the root vnode, which means that
                         * mnt_vnodecovered can be NULL only for the
                         * case of unmount.
                         */
                        if (VN_IS_DOOMED(vp) ||
                            (vp1 = vp->v_mount->mnt_vnodecovered) == NULL ||
                            vp1->v_mountedhere != vp->v_mount) {
                                vput(vp);
                                error = ENOENT;
                                SDT_PROBE3(vfs, namecache, fullpath, return,
                                    error, vp, NULL);
                                break;
                        }

                        vref(vp1);
                        vput(vp);
                        vp = vp1;
                        continue;
                }
                if (vp->v_type != VDIR) {
                        vrele(vp);
                        counter_u64_add(numfullpathfail1, 1);
                        error = ENOTDIR;
                        SDT_PROBE3(vfs, namecache, fullpath, return,
                            error, vp, NULL);
                        break;
                }
                error = vn_vptocnp(&vp, td->td_ucred, buf, &buflen);
                if (error)
                        break;
                if (buflen == 0) {
                        vrele(vp);
                        error = ENOMEM;
                        SDT_PROBE3(vfs, namecache, fullpath, return, error,
                            startvp, NULL);
                        break;
                }
                buf[--buflen] = '/';
                slash_prefixed = 1;
        }
        if (error)
                return (error);
        if (!slash_prefixed) {
                if (buflen == 0) {
                        vrele(vp);
                        counter_u64_add(numfullpathfail4, 1);
                        SDT_PROBE3(vfs, namecache, fullpath, return, ENOMEM,
                            startvp, NULL);
                        return (ENOMEM);
                }
                buf[--buflen] = '/';
        }
        counter_u64_add(numfullpathfound, 1);
        vrele(vp);

        SDT_PROBE3(vfs, namecache, fullpath, return, 0, startvp, buf + buflen);
        *retbuf = buf + buflen;
        return (0);
}

struct vnode *
vn_dir_dd_ino(struct vnode *vp)
{
        struct namecache *ncp;
        struct vnode *ddvp;
        struct mtx *vlp;
        enum vgetstate vs;

        ASSERT_VOP_LOCKED(vp, "vn_dir_dd_ino");
        vlp = VP2VNODELOCK(vp);
        mtx_lock(vlp);
        TAILQ_FOREACH(ncp, &(vp->v_cache_dst), nc_dst) {
                if ((ncp->nc_flag & NCF_ISDOTDOT) != 0)
                        continue;
                ddvp = ncp->nc_dvp;
                vs = vget_prep(ddvp);
                mtx_unlock(vlp);
                if (vget_finish(ddvp, LK_SHARED | LK_NOWAIT, vs))
                        return (NULL);
                return (ddvp);
        }
        mtx_unlock(vlp);
        return (NULL);
}

int
vn_commname(struct vnode *vp, char *buf, u_int buflen)
{
        struct namecache *ncp;
        struct mtx *vlp;
        int l;

        vlp = VP2VNODELOCK(vp);
        mtx_lock(vlp);
        TAILQ_FOREACH(ncp, &vp->v_cache_dst, nc_dst)
                if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
                        break;
        if (ncp == NULL) {
                mtx_unlock(vlp);
                return (ENOENT);
        }
        l = min(ncp->nc_nlen, buflen - 1);
        memcpy(buf, ncp->nc_name, l);
        mtx_unlock(vlp);
        buf[l] = '\0';
        return (0);
}

/*
 * This function updates path string to vnode's full global path
 * and checks the size of the new path string against the pathlen argument.
 *
 * Requires a locked, referenced vnode.
 * Vnode is re-locked on success or ENODEV, otherwise unlocked.
 *
 * If vp is a directory, the call to vn_fullpath_global() always succeeds
 * because it falls back to the ".." lookup if the namecache lookup fails.
 */
int
vn_path_to_global_path(struct thread *td, struct vnode *vp, char *path,
    u_int pathlen)
{
        struct nameidata nd;
        struct vnode *vp1;
        char *rpath, *fbuf;
        int error;

        ASSERT_VOP_ELOCKED(vp, __func__);

        /* Construct global filesystem path from vp. */
        VOP_UNLOCK(vp);
        error = vn_fullpath_global(td, vp, &rpath, &fbuf);

        if (error != 0) {
                vrele(vp);
                return (error);
        }

        if (strlen(rpath) >= pathlen) {
                vrele(vp);
                error = ENAMETOOLONG;
                goto out;
        }

        /*
         * Re-lookup the vnode by path to detect a possible rename.
         * As a side effect, the vnode is relocked.
         * If vnode was renamed, return ENOENT.
         */
        NDINIT(&nd, LOOKUP, FOLLOW | LOCKLEAF | AUDITVNODE1,
            UIO_SYSSPACE, path, td);
        error = namei(&nd);
        if (error != 0) {
                vrele(vp);
                goto out;
        }
        NDFREE(&nd, NDF_ONLY_PNBUF);
        vp1 = nd.ni_vp;
        vrele(vp);
        if (vp1 == vp)
                strcpy(path, rpath);
        else {
                vput(vp1);
                error = ENOENT;
        }

out:
        free(fbuf, M_TEMP);
        return (error);
}

#ifdef DDB
static void
db_print_vpath(struct vnode *vp)
{

        while (vp != NULL) {
                db_printf("%p: ", vp);
                if (vp == rootvnode) {
                        db_printf("/");
                        vp = NULL;
                } else {
                        if (vp->v_vflag & VV_ROOT) {
                                db_printf("<mount point>");
                                vp = vp->v_mount->mnt_vnodecovered;
                        } else {
                                struct namecache *ncp;
                                char *ncn;
                                int i;

                                ncp = TAILQ_FIRST(&vp->v_cache_dst);
                                if (ncp != NULL) {
                                        ncn = ncp->nc_name;
                                        for (i = 0; i < ncp->nc_nlen; i++)
                                                db_printf("%c", *ncn++);
                                        vp = ncp->nc_dvp;
                                } else {
                                        vp = NULL;
                                }
                        }
                }
                db_printf("\n");
        }

        return;
}

DB_SHOW_COMMAND(vpath, db_show_vpath)
{
        struct vnode *vp;

        if (!have_addr) {
                db_printf("usage: show vpath <struct vnode *>\n");
                return;
        }

        vp = (struct vnode *)addr;
        db_print_vpath(vp);
}

#endif