FreeBSD/Linux Kernel Cross Reference
sys/kern/vfs_cache.c

     /*-
      * 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("$FreeBSD: releng/11.1/sys/kern/vfs_cache.c 318367 2017-05-16 19:35:25Z mjg $");
    
    #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/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
    
    #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_DEFINE3(vfs, namecache, zap_negative, done, "struct vnode *",
        "char *", "int");
    SDT_PROBE_DEFINE3(vfs, namecache, shrink_negative, done, "struct vnode *",
        "char *", "int");
    
    /*
     * 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 */
                   u_int   nu_neghits;     /* negative entry hits */
           } 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 {
           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 */
                   u_int   nu_neghits;     /* negative entry hits */
           } n_un;
           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 */
   };
   
   #define nc_vp           n_un.nu_vp
   #define nc_neghits      n_un.nu_neghits
   
   /*
    * 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 (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.
    *
    * 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 = 16; /* 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 */
   SYSCTL_ULONG(_debug, OID_AUTO, numneg, CTLFLAG_RD, &numneg, 0,
       "Number of negative entries in namecache");
   static u_long __exclusive_cache_line    numcache;/* number of cache entries allocated */
   SYSCTL_ULONG(_debug, OID_AUTO, numcache, CTLFLAG_RD, &numcache, 0,
       "Number of namecache entries");
   static u_long __exclusive_cache_line    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");
   u_int __read_mostly     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      ncneghitsrequeue = 8;
   SYSCTL_UINT(_vfs, OID_AUTO, ncneghitsrequeue, CTLFLAG_RW, &ncneghitsrequeue, 0,
       "Number of hits to requeue a negative entry in the LRU list");
   
   struct nchstats nchstats;               /* cache effectiveness statistics */
   
   static struct mtx       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;
   
   #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)
   {
   
           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_flag & NCF_DVDROP) != 0)
                   vdrop(ncp->nc_dvp);
           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 __read_mostly        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_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(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");
   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 cache_lock_vnodes_cel_3_failures;
   STATNODE_ULONG(cache_lock_vnodes_cel_3_failures,
       "Number of times 3-way vnode locking failed");
   
   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, u_int 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
   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(nc_get_name(ncp), 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(x, y)        _cache_sort((void **)(x), (void **)(y))
   static void
   _cache_sort(void **p1, void **p2)
   {
           void *tmp;
   
           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(&vlp1, &vlp2);
           MPASS(vlp2 != NULL);
   
           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_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.
    * Partial LRU for the hot list is maintained by requeueing them every
    * ncneghitsrequeue hits.
    *
    * 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;
           u_int hits;
   
           MPASS(ncp->nc_flag & NCF_NEGATIVE);
           hits = atomic_fetchadd_int(&ncp->nc_neghits, 1);
           if (ncp->nc_flag & NCF_HOTNEGATIVE) {
                   if ((hits % ncneghitsrequeue) != 0)
                           return;
                   mtx_lock(&ncneg_hot.nl_lock);
                   if (ncp->nc_flag & NCF_HOTNEGATIVE) {
                           TAILQ_REMOVE(&ncneg_hot.nl_list, ncp, nc_dst);
                           TAILQ_INSERT_TAIL(&ncneg_hot.nl_list, ncp, nc_dst);
                           mtx_unlock(&ncneg_hot.nl_lock);
                           return;
                   }
                   /*
                    * The shrinker cleared the flag and removed the entry from
                    * the hot list. Put it back.
                    */
           } else {
                   mtx_lock(&ncneg_hot.nl_lock);
           }
           neglist = NCP2NEGLIST(ncp);
           mtx_lock(&neglist->nl_lock);
           if (!(ncp->nc_flag & NCF_HOTNEGATIVE)) {
                   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);
           } 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;
   
           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_trylock(&ncneg_shrink_lock))
                   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;
                   mtx_unlock(&neglist->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);
           if (ncp == NULL) {
                   mtx_unlock(&ncneg_hot.nl_lock);
                   goto out;
           }
   
           MPASS(ncp->nc_flag & NCF_NEGATIVE);
           dvlp = VP2VNODELOCK(ncp->nc_dvp);
           blp = NCP2BUCKETLOCK(ncp);
           mtx_unlock(&neglist->nl_lock);
           mtx_unlock(&ncneg_hot.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;
                   goto out_unlock_all;
           }
           SDT_PROBE3(vfs, namecache, shrink_negative, done, ncp->nc_dvp,
               nc_get_name(ncp), ncp->nc_neghits);
   
           cache_zap_locked(ncp, true);
   out_unlock_all:
           mtx_unlock(&neglist->nl_lock);
           rw_wunlock(blp);
           mtx_unlock(dvlp);
   out:
           mtx_unlock(&ncneg_shrink_lock);
           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);
           if (!(ncp->nc_flag & NCF_NEGATIVE)) {
                   SDT_PROBE3(vfs, namecache, zap, done, ncp->nc_dvp,
                       nc_get_name(ncp), ncp->nc_vp);
           } else {
                   SDT_PROBE3(vfs, namecache, zap_negative, done, ncp->nc_dvp,
                       nc_get_name(ncp), ncp->nc_neghits);
           }
           LIST_REMOVE(ncp, nc_hash);
           if (!(ncp->nc_flag & NCF_NEGATIVE)) {
                   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 {
                   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;
                           atomic_subtract_rel_long(&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(&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
   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(&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);
   }
   
   static int
   cache_zap_rlocked_bucket(struct namecache *ncp, struct rwlock *blp)
   {
           struct mtx *dvlp, *vlp;
   
          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);
          }
  
          rw_runlock(blp);
          return (EAGAIN);
  }
  
  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(&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);
                  mtx_assert(vlp, MA_NOTOWNED);
          } else {
                  mtx_unlock(vlp);
          }
  }
  
  /*
   * 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 caching), 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(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, ltype;
  
          if (__predict_false(!doingcache)) {
                  cnp->cn_flags &= ~MAKEENTRY;
                  return (0);
          }
  retry:
          blp = NULL;
          dvlp = VP2VNODELOCK(dvp);
          error = 0;
          counter_u64_add(numcalls, 1);
  
          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);
                          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 ((*vpp)->v_iflag & VI_DOOMED) {
                                                  /* forced unmount */
                                                  vrele(*vpp);
                                                  *vpp = NULL;
                                                  return (ENOENT);
                                          }
                                  } else
                                          vn_lock(*vpp, LK_DOWNGRADE | LK_RETRY);
                          }
                          return (-1);
                  }
                  if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
                          counter_u64_add(dotdothits, 1);
                          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);
                                  return (0);
                          }
                          if ((cnp->cn_flags & MAKEENTRY) == 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);
                          }
                          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)
                                  *tsp = ((struct namecache_ts *)ncp)->
                                      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(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) {
                          counter_u64_add(nummisszap, 1);
                  } else {
                          counter_u64_add(nummiss, 1);
                  }
                  goto unlock;
          }
  
          /* We don't want to have an entry, so dump it */
          if ((cnp->cn_flags & MAKEENTRY) == 0) {
                  counter_u64_add(numposzaps, 1);
                  goto zap_and_exit;
          }
  
          /* We found a "positive" match, return the vnode */
          if (!(ncp->nc_flag & NCF_NEGATIVE)) {
                  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, 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) {
                  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,
              nc_get_name(ncp));
          cache_out_ts(ncp, tsp, ticksp);
          cache_lookup_unlock(blp, dvlp);
          return (ENOENT);
  
  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, 0);
          }
          vhold(*vpp);
          cache_lookup_unlock(blp, dvlp);
          error = vget(*vpp, cnp->cn_lkflags | LK_VNHELD, 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:
          cache_lookup_unlock(blp, dvlp);
          return (0);
  
  zap_and_exit:
          if (blp != NULL)
                  error = cache_zap_rlocked_bucket(ncp, blp);
          else
                  error = cache_zap_locked_vnode(ncp, dvp);
          if (error != 0) {
                  zap_and_exit_bucket_fail++;
                  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(&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(&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);
  }
  
  /*
   * 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 *n3;
          struct nchashhead *ncpp;
          struct neglist *neglist;
          uint32_t hash;
          int flag;
          int len;
          bool neg_locked;
  
          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 (__predict_false(!doingcache))
                  return;
  
          /*
           * Avoid blowout in namecache entries.
           */
          if (__predict_false(numcache >= desiredvnodes * ncsizefactor))
                  return;
  
          cache_celockstate_init(&cel);
          ndd = NULL;
          flag = 0;
          if (cnp->cn_nameptr[0] == '.') {
                  if (cnp->cn_namelen == 1)
                          return;
                  if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
                          len = cnp->cn_namelen;
                          hash = cache_get_hash(cnp->cn_nameptr, len, dvp);
                          cache_enter_lock_dd(&cel, dvp, vp, hash);
                          /*
                           * 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"));
                                  neg_locked = false;
                                  if (ncp->nc_flag & NCF_NEGATIVE || vp == NULL) {
                                          neglist = NCP2NEGLIST(ncp);
                                          mtx_lock(&ncneg_hot.nl_lock);
                                          mtx_lock(&neglist->nl_lock);
                                          neg_locked = true;
                                  }
                                  if (!(ncp->nc_flag & NCF_NEGATIVE)) {
                                          TAILQ_REMOVE(&ncp->nc_vp->v_cache_dst,
                                              ncp, nc_dst);
                                  } else {
                                          cache_negative_remove(ncp, true);
                                  }
                                  if (vp != NULL) {
                                          TAILQ_INSERT_HEAD(&vp->v_cache_dst,
                                              ncp, nc_dst);
                                          ncp->nc_flag &= ~(NCF_NEGATIVE|NCF_HOTNEGATIVE);
                                  } else {
                                          ncp->nc_flag &= ~(NCF_HOTNEGATIVE);
                                          ncp->nc_flag |= NCF_NEGATIVE;
                                          cache_negative_insert(ncp, true);
                                  }
                                  if (neg_locked) {
                                          mtx_unlock(&neglist->nl_lock);
                                          mtx_unlock(&ncneg_hot.nl_lock);
                                  }
                                  ncp->nc_vp = vp;
                                  cache_enter_unlock(&cel);
                                  return;
                          }
                          dvp->v_cache_dd = NULL;
                          cache_enter_unlock(&cel);
                          cache_celockstate_init(&cel);
                          SDT_PROBE3(vfs, namecache, enter, done, dvp, "..", vp);
                          flag = NCF_ISDOTDOT;
                  }
          }
  
          /*
           * 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) {
                  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 = cache_get_hash(cnp->cn_nameptr, len, dvp);
          strlcpy(nc_get_name(ncp), 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(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;
                                          if (ncp->nc_flag & NCF_NEGATIVE)
                                                  mtx_lock(&ncneg_hot.nl_lock);
                                          n3->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;
          }
  
          atomic_add_rel_long(&numcache, 1);
          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);
                          atomic_add_rel_long(&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, nc_get_name(ncp),
                      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,
                      nc_get_name(ncp));
          }
          cache_enter_unlock(&cel);
          if (numneg * ncnegfactor > numcache)
                  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_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);
          ncbuckethash = cache_roundup_2(mp_ncpus * 64) - 1;
          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 = cache_roundup_2(mp_ncpus * 64) - 1;
          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;
  
          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);
  
          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);
  }
  SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nchinit, NULL);
  
  void
  cache_changesize(int newmaxvnodes)
  {
          struct nchashhead *new_nchashtbl, *old_nchashtbl;
          u_long new_nchash, old_nchash;
          struct namecache *ncp;
          uint32_t hash;
          int i;
  
          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(nc_get_name(ncp), ncp->nc_nlen,
                              ncp->nc_dvp);
                          LIST_REMOVE(ncp, nc_hash);
                          LIST_INSERT_HEAD(NCHHASH(hash), ncp, nc_hash);
                  }
          }
          cache_unlock_all_buckets();
          cache_unlock_all_vnodes();
          free(old_nchashtbl, M_VFSCACHE);
  }
  
  /*
   * Invalidate all entries 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);
          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);
  }
  
  /*
   * XXX All of these sysctls would probably be more productive dead.
   */
  static int __read_mostly disablecwd;
  SYSCTL_INT(_debug, OID_AUTO, disablecwd, CTLFLAG_RW, &disablecwd, 0,
     "Disable the getcwd syscall");
  
  /* 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, u_int buflen,
      u_int path_max)
  {
          char *bp, *tmpbuf;
          struct filedesc *fdp;
          struct vnode *cdir, *rdir;
          int error;
  
          if (__predict_false(disablecwd))
                  return (ENODEV);
          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);
  }
  
  /*
   * Thus begins the fullpath magic.
   */
  
  static int __read_mostly disablefullpath;
  SYSCTL_INT(_debug, OID_AUTO, disablefullpath, CTLFLAG_RW, &disablefullpath, 0,
      "Disable the vn_fullpath function");
  
  /*
   * 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(disablefullpath))
                  return (ENODEV);
          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(disablefullpath))
                  return (ENODEV);
          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, u_int *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, 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);
                  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 (dvp->v_iflag & VI_DOOMED) {
                  /* 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, u_int 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 ((vp->v_iflag & VI_DOOMED) != 0 ||
                              (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;
  
          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;
                  vhold(ddvp);
                  mtx_unlock(vlp);
                  if (vget(ddvp, LK_SHARED | LK_NOWAIT | LK_VNHELD, curthread))
                          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, nc_get_name(ncp), l);
          mtx_unlock(vlp);
          buf[l] = '\0';
          return (0);
  }
  
  /* ABI compat shims for old kernel modules. */
  #undef cache_enter
  
  void    cache_enter(struct vnode *dvp, struct vnode *vp,
              struct componentname *cnp);
  
  void
  cache_enter(struct vnode *dvp, struct vnode *vp, struct componentname *cnp)
  {
  
          cache_enter_time(dvp, vp, 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.
   * 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;
  
          ASSERT_VOP_ELOCKED(vp, __func__);
  
          /* Return ENODEV if sysctl debug.disablefullpath==1 */
          if (__predict_false(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 | 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);
  }

Cache object: 03ba2c83eded711d21b8508e149b4cc1