vfs_cache.c

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/*-
 * 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.
 * 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_cache.c 8.5 (Berkeley) 3/22/95
 */

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

#include "opt_kdtrace.h"
#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/filedesc.h>
#include <sys/fnv_hash.h>
#include <sys/kernel.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/syscallsubr.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/vnode.h>
#ifdef KTRACE
#include <sys/ktrace.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 *");

/*
 * 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 */
        struct  vnode *nc_vp;           /* vnode the name refers to */
        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 {
        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 */
        struct  vnode *nc_vp;           /* vnode the name refers to */
        u_char  nc_flag;                /* flag bits */
        u_char  nc_nlen;                /* length of name */
        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 */
        char    nc_name[0];             /* segment name + nul */
};

/*
 * Flags in namecache.nc_flag
 */
#define NCF_WHITE       0x01
#define NCF_ISDOTDOT    0x02
#define NCF_TS          0x04
#define NCF_DTS         0x08

/*
 * 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 (vp, name) where vp 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.
 */

/*
 * Structures associated with name cacheing.
 */
#define NCHHASH(hash) \
        (&nchashtbl[(hash) & nchash])
static LIST_HEAD(nchashhead, namecache) *nchashtbl;     /* Hash Table */
static TAILQ_HEAD(, namecache) ncneg;   /* Hash Table */
static u_long   nchash;                 /* size of hash table */
SYSCTL_ULONG(_debug, OID_AUTO, nchash, CTLFLAG_RD, &nchash, 0,
    "Size of namecache hash table");
static u_long   ncnegfactor = 16;       /* ratio of negative entries */
SYSCTL_ULONG(_vfs, OID_AUTO, ncnegfactor, CTLFLAG_RW, &ncnegfactor, 0,
    "Ratio of negative namecache entries");
static u_long   numneg;                 /* number of negative entries allocated */
SYSCTL_ULONG(_debug, OID_AUTO, numneg, CTLFLAG_RD, &numneg, 0,
    "Number of negative entries in namecache");
static u_long   numcache;               /* number of cache entries allocated */
SYSCTL_ULONG(_debug, OID_AUTO, numcache, CTLFLAG_RD, &numcache, 0,
    "Number of namecache entries");
static u_long   numcachehv;             /* number of cache entries with vnodes held */
SYSCTL_ULONG(_debug, OID_AUTO, numcachehv, CTLFLAG_RD, &numcachehv, 0,
    "Number of namecache entries with vnodes held");
static u_int    ncsizefactor = 2;
SYSCTL_UINT(_vfs, OID_AUTO, ncsizefactor, CTLFLAG_RW, &ncsizefactor, 0,
    "Size factor for namecache");

struct nchstats nchstats;               /* cache effectiveness statistics */

static struct rwlock cache_lock;
RW_SYSINIT(vfscache, &cache_lock, "Name Cache");

#define CACHE_UPGRADE_LOCK()    rw_try_upgrade(&cache_lock)
#define CACHE_RLOCK()           rw_rlock(&cache_lock)
#define CACHE_RUNLOCK()         rw_runlock(&cache_lock)
#define CACHE_WLOCK()           rw_wlock(&cache_lock)
#define CACHE_WUNLOCK()         rw_wunlock(&cache_lock)

/*
 * 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 cache_zone_small;
static uma_zone_t cache_zone_small_ts;
static uma_zone_t cache_zone_large;
static uma_zone_t cache_zone_large_ts;

#define CACHE_PATH_CUTOFF       35

static struct namecache *
cache_alloc(int len, int ts)
{

        if (len > CACHE_PATH_CUTOFF) {
                if (ts)
                        return (uma_zalloc(cache_zone_large_ts, M_WAITOK));
                else
                        return (uma_zalloc(cache_zone_large, M_WAITOK));
        }
        if (ts)
                return (uma_zalloc(cache_zone_small_ts, M_WAITOK));
        else
                return (uma_zalloc(cache_zone_small, M_WAITOK));
}

static void
cache_free(struct namecache *ncp)
{
        int ts;

        if (ncp == NULL)
                return;
        ts = ncp->nc_flag & NCF_TS;
        if (ncp->nc_nlen <= CACHE_PATH_CUTOFF) {
                if (ts)
                        uma_zfree(cache_zone_small_ts, ncp);
                else
                        uma_zfree(cache_zone_small, ncp);
        } else if (ts)
                uma_zfree(cache_zone_large_ts, ncp);
        else
                uma_zfree(cache_zone_large, ncp);
}

static char *
nc_get_name(struct namecache *ncp)
{
        struct namecache_ts *ncp_ts;

        if ((ncp->nc_flag & NCF_TS) == 0)
                return (ncp->nc_name);
        ncp_ts = (struct namecache_ts *)ncp;
        return (ncp_ts->nc_name);
}

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

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

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

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

/* 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(mode, name, var, descr) \
        SYSCTL_ULONG(_vfs_cache, OID_AUTO, name, mode, var, 0, descr);
STATNODE(CTLFLAG_RD, numneg, &numneg, "Number of negative cache entries");
STATNODE(CTLFLAG_RD, numcache, &numcache, "Number of cache entries");
static u_long numcalls; STATNODE(CTLFLAG_RD, numcalls, &numcalls,
    "Number of cache lookups");
static u_long dothits; STATNODE(CTLFLAG_RD, dothits, &dothits,
    "Number of '.' hits");
static u_long dotdothits; STATNODE(CTLFLAG_RD, dotdothits, &dotdothits,
    "Number of '..' hits");
static u_long numchecks; STATNODE(CTLFLAG_RD, numchecks, &numchecks,
    "Number of checks in lookup");
static u_long nummiss; STATNODE(CTLFLAG_RD, nummiss, &nummiss,
    "Number of cache misses");
static u_long nummisszap; STATNODE(CTLFLAG_RD, nummisszap, &nummisszap,
    "Number of cache misses we do not want to cache");
static u_long numposzaps; STATNODE(CTLFLAG_RD, numposzaps, &numposzaps, 
    "Number of cache hits (positive) we do not want to cache");
static u_long numposhits; STATNODE(CTLFLAG_RD, numposhits, &numposhits,
    "Number of cache hits (positive)");
static u_long numnegzaps; STATNODE(CTLFLAG_RD, numnegzaps, &numnegzaps,
    "Number of cache hits (negative) we do not want to cache");
static u_long numneghits; STATNODE(CTLFLAG_RD, numneghits, &numneghits,
    "Number of cache hits (negative)");
static u_long numupgrades; STATNODE(CTLFLAG_RD, numupgrades, &numupgrades,
    "Number of updates of the cache after lookup (write lock + retry)");

SYSCTL_OPAQUE(_vfs_cache, OID_AUTO, nchstats, CTLFLAG_RD | CTLFLAG_MPSAFE,
    &nchstats, sizeof(nchstats), "LU",
    "VFS cache effectiveness statistics");



static void cache_zap(struct namecache *ncp);
static int vn_vptocnp_locked(struct vnode **vp, struct ucred *cred, char *buf,
    u_int *buflen);
static int vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
    char *buf, char **retbuf, u_int buflen);

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

#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)
{
        int error;
        struct nchashhead *ncpp;
        struct namecache *ncp;
        int n_nchash;
        int count;

        n_nchash = nchash + 1;  /* nchash is max index, not count */
        if (!req->oldptr)
                return SYSCTL_OUT(req, 0, n_nchash * sizeof(int));

        /* Scan hash tables for applicable entries */
        for (ncpp = nchashtbl; n_nchash > 0; n_nchash--, ncpp++) {
                CACHE_RLOCK();
                count = 0;
                LIST_FOREACH(ncp, ncpp, nc_hash) {
                        count++;
                }
                CACHE_RUNLOCK();
                error = SYSCTL_OUT(req, &count, sizeof(count));
                if (error)
                        return (error);
        }
        return (0);
}
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));

        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;
                CACHE_RLOCK();
                LIST_FOREACH(ncp, ncpp, nc_hash) {
                        count++;
                }
                CACHE_RUNLOCK();
                if (count)
                        used++;
                if (maxlength < count)
                        maxlength = count;
        }
        n_nchash = nchash + 1;
        pct = (used * 100 * 100) / n_nchash;
        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 chain lengths");
#endif

/*
 * cache_zap():
 *
 *   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(ncp)
        struct namecache *ncp;
{
        struct vnode *vp;

        rw_assert(&cache_lock, RA_WLOCKED);
        CTR2(KTR_VFS, "cache_zap(%p) vp %p", ncp, ncp->nc_vp);
#ifdef KDTRACE_HOOKS
        if (ncp->nc_vp != NULL) {
                SDT_PROBE3(vfs, namecache, zap, done, ncp->nc_dvp,
                    nc_get_name(ncp), ncp->nc_vp);
        } else {
                SDT_PROBE2(vfs, namecache, zap_negative, done, ncp->nc_dvp,
                    nc_get_name(ncp));
        }
#endif
        vp = NULL;
        LIST_REMOVE(ncp, nc_hash);
        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)) {
                        vp = ncp->nc_dvp;
                        numcachehv--;
                }
        }
        if (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 {
                TAILQ_REMOVE(&ncneg, ncp, nc_dst);
                numneg--;
        }
        numcache--;
        cache_free(ncp);
        if (vp)
                vdrop(vp);
}

/*
 * Lookup an entry in the cache
 *
 * Lookup is called with dvp pointing to the directory to search,
 * cnp pointing to the name of the entry being sought. If the lookup
 * succeeds, the vnode is returned in *vpp, and a status of -1 is
 * returned. If the lookup determines that the name does not exist
 * (negative cacheing), a status of ENOENT is returned. If the lookup
 * fails, a status of zero is returned.  If the directory vnode is
 * recycled out from under us due to a forced unmount, a status of
 * ENOENT is returned.
 *
 * vpp is locked and ref'd on return.  If we're looking up DOTDOT, dvp is
 * unlocked.  If we're looking up . an extra ref is taken, but the lock is
 * not recursively acquired.
 */

int
cache_lookup_times(dvp, vpp, cnp, tsp, ticksp)
        struct vnode *dvp;
        struct vnode **vpp;
        struct componentname *cnp;
        struct timespec *tsp;
        int *ticksp;
{
        struct namecache *ncp;
        uint32_t hash;
        int error, ltype, wlocked;

        if (!doingcache) {
                cnp->cn_flags &= ~MAKEENTRY;
                return (0);
        }
retry:
        CACHE_RLOCK();
        wlocked = 0;
        numcalls++;
        error = 0;

retry_wlocked:
        if (cnp->cn_nameptr[0] == '.') {
                if (cnp->cn_namelen == 1) {
                        *vpp = dvp;
                        CTR2(KTR_VFS, "cache_lookup(%p, %s) found via .",
                            dvp, cnp->cn_nameptr);
                        dothits++;
                        SDT_PROBE3(vfs, namecache, lookup, hit, dvp, ".", *vpp);
                        if (tsp != NULL)
                                timespecclear(tsp);
                        if (ticksp != NULL)
                                *ticksp = ticks;
                        goto success;
                }
                if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
                        dotdothits++;
                        if (dvp->v_cache_dd == NULL) {
                                SDT_PROBE3(vfs, namecache, lookup, miss, dvp,
                                    "..", NULL);
                                goto unlock;
                        }
                        if ((cnp->cn_flags & MAKEENTRY) == 0) {
                                if (!wlocked && !CACHE_UPGRADE_LOCK())
                                        goto wlock;
                                if (dvp->v_cache_dd->nc_flag & NCF_ISDOTDOT)
                                        cache_zap(dvp->v_cache_dd);
                                dvp->v_cache_dd = NULL;
                                CACHE_WUNLOCK();
                                return (0);
                        }
                        ncp = dvp->v_cache_dd;
                        if (ncp->nc_flag & NCF_ISDOTDOT)
                                *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)
                                *tsp = ((struct namecache_ts *)ncp)->
                                    nc_dotdottime;
                        goto success;
                }
        }

        hash = fnv_32_buf(cnp->cn_nameptr, cnp->cn_namelen, FNV1_32_INIT);
        hash = fnv_32_buf(&dvp, sizeof(dvp), hash);
        LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
                numchecks++;
                if (ncp->nc_dvp == dvp && ncp->nc_nlen == cnp->cn_namelen &&
                    !bcmp(nc_get_name(ncp), cnp->cn_nameptr, ncp->nc_nlen))
                        break;
        }

        /* We failed to find an entry */
        if (ncp == NULL) {
                SDT_PROBE3(vfs, namecache, lookup, miss, dvp, cnp->cn_nameptr,
                    NULL);
                if ((cnp->cn_flags & MAKEENTRY) == 0) {
                        nummisszap++;
                } else {
                        nummiss++;
                }
                nchstats.ncs_miss++;
                goto unlock;
        }

        /* We don't want to have an entry, so dump it */
        if ((cnp->cn_flags & MAKEENTRY) == 0) {
                numposzaps++;
                nchstats.ncs_badhits++;
                if (!wlocked && !CACHE_UPGRADE_LOCK())
                        goto wlock;
                cache_zap(ncp);
                CACHE_WUNLOCK();
                return (0);
        }

        /* We found a "positive" match, return the vnode */
        if (ncp->nc_vp) {
                numposhits++;
                nchstats.ncs_goodhits++;
                *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, nc_get_name(ncp),
                    *vpp);
                cache_out_ts(ncp, tsp, ticksp);
                goto success;
        }

negative_success:
        /* We found a negative match, and want to create it, so purge */
        if (cnp->cn_nameiop == CREATE) {
                numnegzaps++;
                nchstats.ncs_badhits++;
                if (!wlocked && !CACHE_UPGRADE_LOCK())
                        goto wlock;
                cache_zap(ncp);
                CACHE_WUNLOCK();
                return (0);
        }

        if (!wlocked && !CACHE_UPGRADE_LOCK())
                goto wlock;
        numneghits++;
        /*
         * We found a "negative" match, so we shift it to the end of
         * the "negative" cache entries queue to satisfy LRU.  Also,
         * check to see if the entry is a whiteout; indicate this to
         * the componentname, if so.
         */
        TAILQ_REMOVE(&ncneg, ncp, nc_dst);
        TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
        nchstats.ncs_neghits++;
        if (ncp->nc_flag & NCF_WHITE)
                cnp->cn_flags |= ISWHITEOUT;
        SDT_PROBE2(vfs, namecache, lookup, hit__negative, dvp,
            nc_get_name(ncp));
        cache_out_ts(ncp, tsp, ticksp);
        CACHE_WUNLOCK();
        return (ENOENT);

wlock:
        /*
         * We need to update the cache after our lookup, so upgrade to
         * a write lock and retry the operation.
         */
        CACHE_RUNLOCK();
        CACHE_WLOCK();
        numupgrades++;
        wlocked = 1;
        goto retry_wlocked;

success:
        /*
         * On success we return a locked and ref'd vnode as per the lookup
         * protocol.
         */
        if (dvp == *vpp) {   /* lookup on "." */
                VREF(*vpp);
                if (wlocked)
                        CACHE_WUNLOCK();
                else
                        CACHE_RUNLOCK();
                /*
                 * 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 ((*vpp)->v_iflag & VI_DOOMED) {
                                        /* forced unmount */
                                        vrele(*vpp);
                                        *vpp = NULL;
                                        return (ENOENT);
                                }
                        } else
                                vn_lock(*vpp, LK_DOWNGRADE | LK_RETRY);
                }
                return (-1);
        }
        ltype = 0;      /* silence gcc warning */
        if (cnp->cn_flags & ISDOTDOT) {
                ltype = VOP_ISLOCKED(dvp);
                VOP_UNLOCK(dvp, 0);
        }
        VI_LOCK(*vpp);
        if (wlocked)
                CACHE_WUNLOCK();
        else
                CACHE_RUNLOCK();
        error = vget(*vpp, cnp->cn_lkflags | LK_INTERLOCK, cnp->cn_thread);
        if (cnp->cn_flags & ISDOTDOT) {
                vn_lock(dvp, ltype | LK_RETRY);
                if (dvp->v_iflag & VI_DOOMED) {
                        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);

unlock:
        if (wlocked)
                CACHE_WUNLOCK();
        else
                CACHE_RUNLOCK();
        return (0);
}

/*
 * Add an entry to the cache.
 */
void
cache_enter_time(dvp, vp, cnp, tsp, dtsp)
        struct vnode *dvp;
        struct vnode *vp;
        struct componentname *cnp;
        struct timespec *tsp;
        struct timespec *dtsp;
{
        struct namecache *ncp, *n2;
        struct namecache_ts *n3;
        struct nchashhead *ncpp;
        uint32_t hash;
        int flag;
        int hold;
        int zap;
        int len;

        CTR3(KTR_VFS, "cache_enter(%p, %p, %s)", dvp, vp, cnp->cn_nameptr);
        VNASSERT(vp == NULL || (vp->v_iflag & VI_DOOMED) == 0, vp,
            ("cache_enter: Adding a doomed vnode"));
        VNASSERT(dvp == NULL || (dvp->v_iflag & VI_DOOMED) == 0, dvp,
            ("cache_enter: Doomed vnode used as src"));

        if (!doingcache)
                return;

        /*
         * Avoid blowout in namecache entries.
         */
        if (numcache >= desiredvnodes * ncsizefactor)
                return;

        flag = 0;
        if (cnp->cn_nameptr[0] == '.') {
                if (cnp->cn_namelen == 1)
                        return;
                if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
                        CACHE_WLOCK();
                        /*
                         * If dotdot entry already exists, just retarget it
                         * to new parent vnode, otherwise continue with new
                         * namecache entry allocation.
                         */
                        if ((ncp = dvp->v_cache_dd) != NULL &&
                            ncp->nc_flag & NCF_ISDOTDOT) {
                                KASSERT(ncp->nc_dvp == dvp,
                                    ("wrong isdotdot parent"));
                                if (ncp->nc_vp != NULL) {
                                        TAILQ_REMOVE(&ncp->nc_vp->v_cache_dst,
                                            ncp, nc_dst);
                                } else {
                                        TAILQ_REMOVE(&ncneg, ncp, nc_dst);
                                        numneg--;
                                }
                                if (vp != NULL) {
                                        TAILQ_INSERT_HEAD(&vp->v_cache_dst,
                                            ncp, nc_dst);
                                } else {
                                        TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
                                        numneg++;
                                }
                                ncp->nc_vp = vp;
                                CACHE_WUNLOCK();
                                return;
                        }
                        dvp->v_cache_dd = NULL;
                        SDT_PROBE3(vfs, namecache, enter, done, dvp, "..", vp);
                        CACHE_WUNLOCK();
                        flag = NCF_ISDOTDOT;
                }
        }

        hold = 0;
        zap = 0;

        /*
         * 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_vp = vp;
        ncp->nc_dvp = dvp;
        ncp->nc_flag = flag;
        if (tsp != NULL) {
                n3 = (struct namecache_ts *)ncp;
                n3->nc_time = *tsp;
                n3->nc_ticks = ticks;
                n3->nc_flag |= NCF_TS;
                if (dtsp != NULL) {
                        n3->nc_dotdottime = *dtsp;
                        n3->nc_flag |= NCF_DTS;
                }
        }
        len = ncp->nc_nlen = cnp->cn_namelen;
        hash = fnv_32_buf(cnp->cn_nameptr, len, FNV1_32_INIT);
        strlcpy(nc_get_name(ncp), cnp->cn_nameptr, len + 1);
        hash = fnv_32_buf(&dvp, sizeof(dvp), hash);
        CACHE_WLOCK();

        /*
         * 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(nc_get_name(n2), cnp->cn_nameptr, n2->nc_nlen)) {
                        if (tsp != NULL) {
                                KASSERT((n2->nc_flag & NCF_TS) != 0,
                                    ("no NCF_TS"));
                                n3 = (struct namecache_ts *)n2;
                                n3->nc_time =
                                    ((struct namecache_ts *)ncp)->nc_time;
                                n3->nc_ticks =
                                    ((struct namecache_ts *)ncp)->nc_ticks;
                                if (dtsp != NULL) {
                                        n3->nc_dotdottime =
                                            ((struct namecache_ts *)ncp)->
                                            nc_dotdottime;
                                        n3->nc_flag |= NCF_DTS;
                                }
                        }
                        CACHE_WUNLOCK();
                        cache_free(ncp);
                        return;
                }
        }

        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) {
                    CACHE_WUNLOCK();
                    cache_free(ncp);
                    return;
                }
                KASSERT(vp == NULL || vp->v_type == VDIR,
                    ("wrong vnode type %p", vp));
                dvp->v_cache_dd = ncp;
        }

        numcache++;
        if (!vp) {
                numneg++;
                if (cnp->cn_flags & ISWHITEOUT)
                        ncp->nc_flag |= NCF_WHITE;
        } else 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 ((n2 = vp->v_cache_dd) != NULL &&
                            (n2->nc_flag & NCF_ISDOTDOT) != 0)
                                cache_zap(n2);
                        vp->v_cache_dd = ncp;
                }
        } else {
                vp->v_cache_dd = NULL;
        }

        /*
         * Insert the new namecache entry into the appropriate chain
         * within the cache entries table.
         */
        LIST_INSERT_HEAD(ncpp, ncp, nc_hash);
        if (flag != NCF_ISDOTDOT) {
                if (LIST_EMPTY(&dvp->v_cache_src)) {
                        hold = 1;
                        numcachehv++;
                }
                LIST_INSERT_HEAD(&dvp->v_cache_src, ncp, nc_src);
        }

        /*
         * 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) {
                TAILQ_INSERT_HEAD(&vp->v_cache_dst, ncp, nc_dst);
                SDT_PROBE3(vfs, namecache, enter, done, dvp, nc_get_name(ncp),
                    vp);
        } else {
                TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
                SDT_PROBE2(vfs, namecache, enter_negative, done, dvp,
                    nc_get_name(ncp));
        }
        if (numneg * ncnegfactor > numcache) {
                ncp = TAILQ_FIRST(&ncneg);
                KASSERT(ncp->nc_vp == NULL, ("ncp %p vp %p on ncneg",
                    ncp, ncp->nc_vp));
                zap = 1;
        }
        if (hold)
                vhold(dvp);
        if (zap)
                cache_zap(ncp);
        CACHE_WUNLOCK();
}

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

        TAILQ_INIT(&ncneg);

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

        nchashtbl = hashinit(desiredvnodes * 2, M_VFSCACHE, &nchash);
}
SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nchinit, NULL);


/*
 * Invalidate all entries to a particular vnode.
 */
void
cache_purge(vp)
        struct vnode *vp;
{

        CTR1(KTR_VFS, "cache_purge(%p)", vp);
        SDT_PROBE1(vfs, namecache, purge, done, vp);
        CACHE_WLOCK();
        while (!LIST_EMPTY(&vp->v_cache_src))
                cache_zap(LIST_FIRST(&vp->v_cache_src));
        while (!TAILQ_EMPTY(&vp->v_cache_dst))
                cache_zap(TAILQ_FIRST(&vp->v_cache_dst));
        if (vp->v_cache_dd != NULL) {
                KASSERT(vp->v_cache_dd->nc_flag & NCF_ISDOTDOT,
                   ("lost dotdot link"));
                cache_zap(vp->v_cache_dd);
        }
        KASSERT(vp->v_cache_dd == NULL, ("incomplete purge"));
        CACHE_WUNLOCK();
}

/*
 * Invalidate all negative entries for a particular directory vnode.
 */
void
cache_purge_negative(vp)
        struct vnode *vp;
{
        struct namecache *cp, *ncp;

        CTR1(KTR_VFS, "cache_purge_negative(%p)", vp);
        SDT_PROBE1(vfs, namecache, purge_negative, done, vp);
        CACHE_WLOCK();
        LIST_FOREACH_SAFE(cp, &vp->v_cache_src, nc_src, ncp) {
                if (cp->nc_vp == NULL)
                        cache_zap(cp);
        }
        CACHE_WUNLOCK();
}

/*
 * Flush all entries referencing a particular filesystem.
 */
void
cache_purgevfs(mp)
        struct mount *mp;
{
        struct nchashhead *ncpp;
        struct namecache *ncp, *nnp;

        /* Scan hash tables for applicable entries */
        SDT_PROBE1(vfs, namecache, purgevfs, done, mp);
        CACHE_WLOCK();
        for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
                LIST_FOREACH_SAFE(ncp, ncpp, nc_hash, nnp) {
                        if (ncp->nc_dvp->v_mount == mp)
                                cache_zap(ncp);
                }
        }
        CACHE_WUNLOCK();
}

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

int
vfs_cache_lookup(ap)
        struct vop_lookup_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
        } */ *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);
        if (error == 0)
                return (VOP_CACHEDLOOKUP(dvp, vpp, cnp));
        if (error == -1)
                return (0);
        return (error);
}

/*
 * XXX All of these sysctls would probably be more productive dead.
 */
static int disablecwd;
SYSCTL_INT(_debug, OID_AUTO, disablecwd, CTLFLAG_RW, &disablecwd, 0,
   "Disable the getcwd syscall");

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

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

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

        if (disablecwd)
                return (ENODEV);
        if (buflen < 2)
                return (EINVAL);
        if (buflen > MAXPATHLEN)
                buflen = MAXPATHLEN;

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

        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);
}

/*
 * Thus begins the fullpath magic.
 */

#undef STATNODE
#define STATNODE(name, descr)                                           \
        static u_int name;                                              \
        SYSCTL_UINT(_vfs_cache, OID_AUTO, name, CTLFLAG_RD, &name, 0, descr)

static int disablefullpath;
SYSCTL_INT(_debug, OID_AUTO, disablefullpath, CTLFLAG_RW, &disablefullpath, 0,
    "Disable the vn_fullpath function");

/* These count for kern___getcwd(), too. */
STATNODE(numfullpathcalls, "Number of fullpath search calls");
STATNODE(numfullpathfail1, "Number of fullpath search errors (ENOTDIR)");
STATNODE(numfullpathfail2,
    "Number of fullpath search errors (VOP_VPTOCNP failures)");
STATNODE(numfullpathfail4, "Number of fullpath search errors (ENOMEM)");
STATNODE(numfullpathfound, "Number of successful fullpath calls");

/*
 * 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, vfslocked;

        if (disablefullpath)
                return (ENODEV);
        if (vn == NULL)
                return (EINVAL);

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

        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 (disablefullpath)
                return (ENODEV);
        if (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, u_int *buflen)
{
        int error;

        CACHE_RLOCK();
        error = vn_vptocnp_locked(vp, cred, buf, buflen);
        if (error == 0)
                CACHE_RUNLOCK();
        return (error);
}

static int
vn_vptocnp_locked(struct vnode **vp, struct ucred *cred, char *buf,
    u_int *buflen)
{
        struct vnode *dvp;
        struct namecache *ncp;
        int error, vfslocked;

        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) {
                        CACHE_RUNLOCK();
                        vfslocked = VFS_LOCK_GIANT((*vp)->v_mount);
                        vrele(*vp);
                        VFS_UNLOCK_GIANT(vfslocked);
                        numfullpathfail4++;
                        error = ENOMEM;
                        SDT_PROBE3(vfs, namecache, fullpath, return, error,
                            vp, NULL);
                        return (error);
                }
                *buflen -= ncp->nc_nlen;
                memcpy(buf + *buflen, nc_get_name(ncp), ncp->nc_nlen);
                SDT_PROBE3(vfs, namecache, fullpath, hit, ncp->nc_dvp,
                    nc_get_name(ncp), vp);
                dvp = *vp;
                *vp = ncp->nc_dvp;
                vref(*vp);
                CACHE_RUNLOCK();
                vfslocked = VFS_LOCK_GIANT(dvp->v_mount);
                vrele(dvp);
                VFS_UNLOCK_GIANT(vfslocked);
                CACHE_RLOCK();
                return (0);
        }
        SDT_PROBE1(vfs, namecache, fullpath, miss, vp);

        CACHE_RUNLOCK();
        vfslocked = VFS_LOCK_GIANT((*vp)->v_mount);
        vn_lock(*vp, LK_SHARED | LK_RETRY);
        error = VOP_VPTOCNP(*vp, &dvp, cred, buf, buflen);
        vput(*vp);
        VFS_UNLOCK_GIANT(vfslocked);
        if (error) {
                numfullpathfail2++;
                SDT_PROBE3(vfs, namecache, fullpath, return,  error, vp, NULL);
                return (error);
        }

        *vp = dvp;
        CACHE_RLOCK();
        if (dvp->v_iflag & VI_DOOMED) {
                /* forced unmount */
                CACHE_RUNLOCK();
                vfslocked = VFS_LOCK_GIANT(dvp->v_mount);
                vrele(dvp);
                VFS_UNLOCK_GIANT(vfslocked);
                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, u_int buflen)
{
        int error, slash_prefixed, vfslocked;
#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);
        numfullpathcalls++;
        vref(vp);
        CACHE_RLOCK();
        if (vp->v_type != VDIR) {
                error = vn_vptocnp_locked(&vp, td->td_ucred, buf, &buflen);
                if (error)
                        return (error);
                if (buflen == 0) {
                        CACHE_RUNLOCK();
                        vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                        vrele(vp);
                        VFS_UNLOCK_GIANT(vfslocked);
                        return (ENOMEM);
                }
                buf[--buflen] = '/';
                slash_prefixed = 1;
        }
        while (vp != rdir && vp != rootvnode) {
                if (vp->v_vflag & VV_ROOT) {
                        if (vp->v_iflag & VI_DOOMED) {  /* forced unmount */
                                CACHE_RUNLOCK();
                                vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                                vrele(vp);
                                VFS_UNLOCK_GIANT(vfslocked);
                                error = ENOENT;
                                SDT_PROBE3(vfs, namecache, fullpath, return,
                                    error, vp, NULL);
                                break;
                        }
                        vp1 = vp->v_mount->mnt_vnodecovered;
                        vref(vp1);
                        CACHE_RUNLOCK();
                        vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                        vrele(vp);
                        VFS_UNLOCK_GIANT(vfslocked);
                        vp = vp1;
                        CACHE_RLOCK();
                        continue;
                }
                if (vp->v_type != VDIR) {
                        CACHE_RUNLOCK();
                        vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                        vrele(vp);
                        VFS_UNLOCK_GIANT(vfslocked);
                        numfullpathfail1++;
                        error = ENOTDIR;
                        SDT_PROBE3(vfs, namecache, fullpath, return,
                            error, vp, NULL);
                        break;
                }
                error = vn_vptocnp_locked(&vp, td->td_ucred, buf, &buflen);
                if (error)
                        break;
                if (buflen == 0) {
                        CACHE_RUNLOCK();
                        vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                        vrele(vp);
                        VFS_UNLOCK_GIANT(vfslocked);
                        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) {
                        CACHE_RUNLOCK();
                        vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                        vrele(vp);
                        VFS_UNLOCK_GIANT(vfslocked);
                        numfullpathfail4++;
                        SDT_PROBE3(vfs, namecache, fullpath, return, ENOMEM,
                            startvp, NULL);
                        return (ENOMEM);
                }
                buf[--buflen] = '/';
        }
        numfullpathfound++;
        CACHE_RUNLOCK();
        vfslocked = VFS_LOCK_GIANT(vp->v_mount);
        vrele(vp);
        VFS_UNLOCK_GIANT(vfslocked);

        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;

        ASSERT_VOP_LOCKED(vp, "vn_dir_dd_ino");
        CACHE_RLOCK();
        TAILQ_FOREACH(ncp, &(vp->v_cache_dst), nc_dst) {
                if ((ncp->nc_flag & NCF_ISDOTDOT) != 0)
                        continue;
                ddvp = ncp->nc_dvp;
                VI_LOCK(ddvp);
                CACHE_RUNLOCK();
                if (vget(ddvp, LK_INTERLOCK | LK_SHARED | LK_NOWAIT, curthread))
                        return (NULL);
                return (ddvp);
        }
        CACHE_RUNLOCK();
        return (NULL);
}

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

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

/* ABI compat shims for old kernel modules. */
#undef cache_enter
#undef cache_lookup

void    cache_enter(struct vnode *dvp, struct vnode *vp,
            struct componentname *cnp);
int     cache_lookup(struct vnode *dvp, struct vnode **vpp,
            struct componentname *cnp);

void
cache_enter(struct vnode *dvp, struct vnode *vp, struct componentname *cnp)
{

        cache_enter_time(dvp, vp, cnp, NULL, NULL);
}

int
cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
{

        return (cache_lookup_times(dvp, vpp, cnp, NULL, NULL));
}

/*
 * 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 and GIANT lock held.
 * Vnode is re-locked on success or ENODEV, otherwise unlocked.
 *
 * If sysctl debug.disablefullpath is set, ENODEV is returned,
 * vnode is left locked and path remain untouched.
 *
 * 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, vfslocked;

        VFS_ASSERT_GIANT(vp->v_mount);
        ASSERT_VOP_ELOCKED(vp, __func__);

        /* Return ENODEV if sysctl debug.disablefullpath==1 */
        if (disablefullpath)
                return (ENODEV);

        /* Construct global filesystem path from vp. */
        VOP_UNLOCK(vp, 0);
        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 | MPSAFE | AUDITVNODE1,
            UIO_SYSSPACE, path, td);
        error = namei(&nd);
        if (error != 0) {
                vrele(vp);
                goto out;
        }
        vfslocked = NDHASGIANT(&nd);
        NDFREE(&nd, NDF_ONLY_PNBUF);
        vp1 = nd.ni_vp;
        vrele(vp);
        if (vp1 == vp)
                strcpy(path, rpath);
        else {
                vput(vp1);
                error = ENOENT;
        }
        VFS_UNLOCK_GIANT(vfslocked);

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