2 * Copyright (c) 1989, 1993, 1995
3 * The Regents of the University of California. All rights reserved.
5 * This code is derived from software contributed to Berkeley by
6 * Poul-Henning Kamp of the FreeBSD Project.
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 4. Neither the name of the University nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
18 * without specific prior written permission.
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * @(#)vfs_cache.c 8.5 (Berkeley) 3/22/95
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
38 #include <sys/param.h>
39 #include <sys/systm.h>
40 #include <sys/kernel.h>
42 #include <sys/mutex.h>
43 #include <sys/sysctl.h>
44 #include <sys/mount.h>
45 #include <sys/vnode.h>
46 #include <sys/namei.h>
47 #include <sys/malloc.h>
48 #include <sys/syscallsubr.h>
49 #include <sys/sysproto.h>
51 #include <sys/filedesc.h>
52 #include <sys/fnv_hash.h>
57 * This structure describes the elements in the cache of recent
58 * names looked up by namei.
62 LIST_ENTRY(namecache) nc_hash; /* hash chain */
63 LIST_ENTRY(namecache) nc_src; /* source vnode list */
64 TAILQ_ENTRY(namecache) nc_dst; /* destination vnode list */
65 struct vnode *nc_dvp; /* vnode of parent of name */
66 struct vnode *nc_vp; /* vnode the name refers to */
67 u_char nc_flag; /* flag bits */
68 u_char nc_nlen; /* length of name */
69 char nc_name[0]; /* segment name */
73 * Name caching works as follows:
75 * Names found by directory scans are retained in a cache
76 * for future reference. It is managed LRU, so frequently
77 * used names will hang around. Cache is indexed by hash value
78 * obtained from (vp, name) where vp refers to the directory
81 * If it is a "negative" entry, (i.e. for a name that is known NOT to
82 * exist) the vnode pointer will be NULL.
84 * Upon reaching the last segment of a path, if the reference
85 * is for DELETE, or NOCACHE is set (rewrite), and the
86 * name is located in the cache, it will be dropped.
90 * Structures associated with name cacheing.
92 #define NCHHASH(hash) \
93 (&nchashtbl[(hash) & nchash])
94 static LIST_HEAD(nchashhead, namecache) *nchashtbl; /* Hash Table */
95 static TAILQ_HEAD(, namecache) ncneg; /* Hash Table */
96 static u_long nchash; /* size of hash table */
97 SYSCTL_ULONG(_debug, OID_AUTO, nchash, CTLFLAG_RD, &nchash, 0, "");
98 static u_long ncnegfactor = 16; /* ratio of negative entries */
99 SYSCTL_ULONG(_debug, OID_AUTO, ncnegfactor, CTLFLAG_RW, &ncnegfactor, 0, "");
100 static u_long numneg; /* number of cache entries allocated */
101 SYSCTL_ULONG(_debug, OID_AUTO, numneg, CTLFLAG_RD, &numneg, 0, "");
102 static u_long numcache; /* number of cache entries allocated */
103 SYSCTL_ULONG(_debug, OID_AUTO, numcache, CTLFLAG_RD, &numcache, 0, "");
104 static u_long numcachehv; /* number of cache entries with vnodes held */
105 SYSCTL_ULONG(_debug, OID_AUTO, numcachehv, CTLFLAG_RD, &numcachehv, 0, "");
107 static u_long numcachepl; /* number of cache purge for leaf entries */
108 SYSCTL_ULONG(_debug, OID_AUTO, numcachepl, CTLFLAG_RD, &numcachepl, 0, "");
110 struct nchstats nchstats; /* cache effectiveness statistics */
112 static struct mtx cache_lock;
113 MTX_SYSINIT(vfscache, &cache_lock, "Name Cache", MTX_DEF);
115 #define CACHE_LOCK() mtx_lock(&cache_lock)
116 #define CACHE_UNLOCK() mtx_unlock(&cache_lock)
119 * UMA zones for the VFS cache.
121 * The small cache is used for entries with short names, which are the
122 * most common. The large cache is used for entries which are too big to
123 * fit in the small cache.
125 static uma_zone_t cache_zone_small;
126 static uma_zone_t cache_zone_large;
128 #define CACHE_PATH_CUTOFF 32
129 #define CACHE_ZONE_SMALL (sizeof(struct namecache) + CACHE_PATH_CUTOFF)
130 #define CACHE_ZONE_LARGE (sizeof(struct namecache) + NAME_MAX)
132 #define cache_alloc(len) uma_zalloc(((len) <= CACHE_PATH_CUTOFF) ? \
133 cache_zone_small : cache_zone_large, M_WAITOK)
134 #define cache_free(ncp) do { \
136 uma_zfree(((ncp)->nc_nlen <= CACHE_PATH_CUTOFF) ? \
137 cache_zone_small : cache_zone_large, (ncp)); \
140 static int doingcache = 1; /* 1 => enable the cache */
141 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, "");
143 /* Export size information to userland */
144 SYSCTL_INT(_debug, OID_AUTO, vnsize, CTLFLAG_RD, 0, sizeof(struct vnode), "");
145 SYSCTL_INT(_debug, OID_AUTO, ncsize, CTLFLAG_RD, 0, sizeof(struct namecache), "");
148 * The new name cache statistics
150 static SYSCTL_NODE(_vfs, OID_AUTO, cache, CTLFLAG_RW, 0, "Name cache statistics");
151 #define STATNODE(mode, name, var) \
152 SYSCTL_ULONG(_vfs_cache, OID_AUTO, name, mode, var, 0, "");
153 STATNODE(CTLFLAG_RD, numneg, &numneg);
154 STATNODE(CTLFLAG_RD, numcache, &numcache);
155 static u_long numcalls; STATNODE(CTLFLAG_RD, numcalls, &numcalls);
156 static u_long dothits; STATNODE(CTLFLAG_RD, dothits, &dothits);
157 static u_long dotdothits; STATNODE(CTLFLAG_RD, dotdothits, &dotdothits);
158 static u_long numchecks; STATNODE(CTLFLAG_RD, numchecks, &numchecks);
159 static u_long nummiss; STATNODE(CTLFLAG_RD, nummiss, &nummiss);
160 static u_long nummisszap; STATNODE(CTLFLAG_RD, nummisszap, &nummisszap);
161 static u_long numposzaps; STATNODE(CTLFLAG_RD, numposzaps, &numposzaps);
162 static u_long numposhits; STATNODE(CTLFLAG_RD, numposhits, &numposhits);
163 static u_long numnegzaps; STATNODE(CTLFLAG_RD, numnegzaps, &numnegzaps);
164 static u_long numneghits; STATNODE(CTLFLAG_RD, numneghits, &numneghits);
166 SYSCTL_OPAQUE(_vfs_cache, OID_AUTO, nchstats, CTLFLAG_RD, &nchstats,
167 sizeof(nchstats), "LU", "VFS cache effectiveness statistics");
171 static void cache_zap(struct namecache *ncp);
172 static int vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
173 char *buf, char **retbuf, u_int buflen);
175 static MALLOC_DEFINE(M_VFSCACHE, "vfscache", "VFS name cache entries");
178 * Flags in namecache.nc_flag
183 * Grab an atomic snapshot of the name cache hash chain lengths
185 SYSCTL_NODE(_debug, OID_AUTO, hashstat, CTLFLAG_RW, NULL, "hash table stats");
188 sysctl_debug_hashstat_rawnchash(SYSCTL_HANDLER_ARGS)
191 struct nchashhead *ncpp;
192 struct namecache *ncp;
196 n_nchash = nchash + 1; /* nchash is max index, not count */
198 return SYSCTL_OUT(req, 0, n_nchash * sizeof(int));
200 /* Scan hash tables for applicable entries */
201 for (ncpp = nchashtbl; n_nchash > 0; n_nchash--, ncpp++) {
203 LIST_FOREACH(ncp, ncpp, nc_hash) {
206 error = SYSCTL_OUT(req, &count, sizeof(count));
212 SYSCTL_PROC(_debug_hashstat, OID_AUTO, rawnchash, CTLTYPE_INT|CTLFLAG_RD,
213 0, 0, sysctl_debug_hashstat_rawnchash, "S,int", "nchash chain lengths");
216 sysctl_debug_hashstat_nchash(SYSCTL_HANDLER_ARGS)
219 struct nchashhead *ncpp;
220 struct namecache *ncp;
222 int count, maxlength, used, pct;
225 return SYSCTL_OUT(req, 0, 4 * sizeof(int));
227 n_nchash = nchash + 1; /* nchash is max index, not count */
231 /* Scan hash tables for applicable entries */
232 for (ncpp = nchashtbl; n_nchash > 0; n_nchash--, ncpp++) {
234 LIST_FOREACH(ncp, ncpp, nc_hash) {
239 if (maxlength < count)
242 n_nchash = nchash + 1;
243 pct = (used * 100 * 100) / n_nchash;
244 error = SYSCTL_OUT(req, &n_nchash, sizeof(n_nchash));
247 error = SYSCTL_OUT(req, &used, sizeof(used));
250 error = SYSCTL_OUT(req, &maxlength, sizeof(maxlength));
253 error = SYSCTL_OUT(req, &pct, sizeof(pct));
258 SYSCTL_PROC(_debug_hashstat, OID_AUTO, nchash, CTLTYPE_INT|CTLFLAG_RD,
259 0, 0, sysctl_debug_hashstat_nchash, "I", "nchash chain lengths");
264 * Removes a namecache entry from cache, whether it contains an actual
265 * pointer to a vnode or if it is just a negative cache entry.
269 struct namecache *ncp;
273 mtx_assert(&cache_lock, MA_OWNED);
274 CTR2(KTR_VFS, "cache_zap(%p) vp %p", ncp, ncp->nc_vp);
276 LIST_REMOVE(ncp, nc_hash);
277 LIST_REMOVE(ncp, nc_src);
278 if (LIST_EMPTY(&ncp->nc_dvp->v_cache_src)) {
283 TAILQ_REMOVE(&ncp->nc_vp->v_cache_dst, ncp, nc_dst);
284 ncp->nc_vp->v_dd = NULL;
286 TAILQ_REMOVE(&ncneg, ncp, nc_dst);
298 * Test whether this (directory) vnode's namei cache entry contains
299 * subdirectories or not. Used to determine whether the directory is
300 * a leaf in the namei cache or not. Note: the directory may still
301 * contain files in the namei cache.
303 * Returns 0 if the directory is a leaf, -1 if it isn't.
306 cache_leaf_test(struct vnode *vp)
308 struct namecache *ncpc;
313 for (ncpc = LIST_FIRST(&vp->v_cache_src);
315 ncpc = LIST_NEXT(ncpc, nc_src)
317 if (ncpc->nc_vp != NULL && ncpc->nc_vp->v_type == VDIR) {
327 * Lookup an entry in the cache
329 * Lookup is called with dvp pointing to the directory to search,
330 * cnp pointing to the name of the entry being sought. If the lookup
331 * succeeds, the vnode is returned in *vpp, and a status of -1 is
332 * returned. If the lookup determines that the name does not exist
333 * (negative cacheing), a status of ENOENT is returned. If the lookup
334 * fails, a status of zero is returned.
336 * vpp is locked and ref'd on return. If we're looking up DOTDOT, dvp is
337 * unlocked. If we're looking up . an extra ref is taken, but the lock is
338 * not recursively acquired.
342 cache_lookup(dvp, vpp, cnp)
345 struct componentname *cnp;
347 struct namecache *ncp;
352 cnp->cn_flags &= ~MAKEENTRY;
359 if (cnp->cn_nameptr[0] == '.') {
360 if (cnp->cn_namelen == 1) {
362 CTR2(KTR_VFS, "cache_lookup(%p, %s) found via .",
363 dvp, cnp->cn_nameptr);
367 if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
369 if (dvp->v_dd == NULL ||
370 (cnp->cn_flags & MAKEENTRY) == 0) {
375 CTR3(KTR_VFS, "cache_lookup(%p, %s) found %p via ..",
376 dvp, cnp->cn_nameptr, *vpp);
381 hash = fnv_32_buf(cnp->cn_nameptr, cnp->cn_namelen, FNV1_32_INIT);
382 hash = fnv_32_buf(&dvp, sizeof(dvp), hash);
383 LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
385 if (ncp->nc_dvp == dvp && ncp->nc_nlen == cnp->cn_namelen &&
386 !bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen))
390 /* We failed to find an entry */
392 if ((cnp->cn_flags & MAKEENTRY) == 0) {
402 /* We don't want to have an entry, so dump it */
403 if ((cnp->cn_flags & MAKEENTRY) == 0) {
405 nchstats.ncs_badhits++;
411 /* We found a "positive" match, return the vnode */
414 nchstats.ncs_goodhits++;
416 CTR4(KTR_VFS, "cache_lookup(%p, %s) found %p via ncp %p",
417 dvp, cnp->cn_nameptr, *vpp, ncp);
421 /* We found a negative match, and want to create it, so purge */
422 if (cnp->cn_nameiop == CREATE) {
424 nchstats.ncs_badhits++;
432 * We found a "negative" match, so we shift it to the end of
433 * the "negative" cache entries queue to satisfy LRU. Also,
434 * check to see if the entry is a whiteout; indicate this to
435 * the componentname, if so.
437 TAILQ_REMOVE(&ncneg, ncp, nc_dst);
438 TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
439 nchstats.ncs_neghits++;
440 if (ncp->nc_flag & NCF_WHITE)
441 cnp->cn_flags |= ISWHITEOUT;
447 * On success we return a locked and ref'd vnode as per the lookup
450 if (dvp == *vpp) { /* lookup on "." */
455 if (cnp->cn_flags & ISDOTDOT)
456 VOP_UNLOCK(dvp, 0, cnp->cn_thread);
459 error = vget(*vpp, cnp->cn_lkflags | LK_INTERLOCK, cnp->cn_thread);
460 if (cnp->cn_flags & ISDOTDOT)
461 vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY, cnp->cn_thread);
470 * Add an entry to the cache.
473 cache_enter(dvp, vp, cnp)
476 struct componentname *cnp;
478 struct namecache *ncp;
479 struct nchashhead *ncpp;
485 CTR3(KTR_VFS, "cache_enter(%p, %p, %s)", dvp, vp, cnp->cn_nameptr);
486 VNASSERT(vp == NULL || (vp->v_iflag & VI_DOOMED) == 0, vp,
487 ("cahe_enter: Adding a doomed vnode"));
492 if (cnp->cn_nameptr[0] == '.') {
493 if (cnp->cn_namelen == 1) {
497 * For dotdot lookups only cache the v_dd pointer if the
498 * directory has a link back to its parent via v_cache_dst.
499 * Without this an unlinked directory would keep a soft
500 * reference to its parent which could not be NULLd at
501 * cache_purge() time.
503 if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
505 if (!TAILQ_EMPTY(&dvp->v_cache_dst))
514 ncp = cache_alloc(cnp->cn_namelen);
519 ncp->nc_flag = cnp->cn_flags & ISWHITEOUT ? NCF_WHITE : 0;
520 } else if (vp->v_type == VDIR) {
527 * Set the rest of the namecache entry elements, calculate it's
528 * hash key and insert it into the appropriate chain within
529 * the cache entries table.
533 len = ncp->nc_nlen = cnp->cn_namelen;
534 hash = fnv_32_buf(cnp->cn_nameptr, len, FNV1_32_INIT);
535 bcopy(cnp->cn_nameptr, ncp->nc_name, len);
536 hash = fnv_32_buf(&dvp, sizeof(dvp), hash);
537 ncpp = NCHHASH(hash);
538 LIST_INSERT_HEAD(ncpp, ncp, nc_hash);
539 if (LIST_EMPTY(&dvp->v_cache_src)) {
543 LIST_INSERT_HEAD(&dvp->v_cache_src, ncp, nc_src);
545 * If the entry is "negative", we place it into the
546 * "negative" cache queue, otherwise, we place it into the
547 * destination vnode's cache entries queue.
550 TAILQ_INSERT_HEAD(&vp->v_cache_dst, ncp, nc_dst);
552 TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
554 if (numneg * ncnegfactor > numcache) {
555 ncp = TAILQ_FIRST(&ncneg);
566 * Name cache initialization, from vfs_init() when we are booting
569 nchinit(void *dummy __unused)
574 cache_zone_small = uma_zcreate("S VFS Cache", CACHE_ZONE_SMALL, NULL,
575 NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_ZINIT);
576 cache_zone_large = uma_zcreate("L VFS Cache", CACHE_ZONE_LARGE, NULL,
577 NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_ZINIT);
579 nchashtbl = hashinit(desiredvnodes * 2, M_VFSCACHE, &nchash);
581 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nchinit, NULL)
585 * Invalidate all entries to a particular vnode.
592 CTR1(KTR_VFS, "cache_purge(%p)", vp);
594 while (!LIST_EMPTY(&vp->v_cache_src))
595 cache_zap(LIST_FIRST(&vp->v_cache_src));
596 while (!TAILQ_EMPTY(&vp->v_cache_dst))
597 cache_zap(TAILQ_FIRST(&vp->v_cache_dst));
603 * Flush all entries referencing a particular filesystem.
605 * Since we need to check it anyway, we will flush all the invalid
606 * entries at the same time.
612 struct nchashhead *ncpp;
613 struct namecache *ncp, *nnp;
614 struct nchashhead mplist;
619 /* Scan hash tables for applicable entries */
621 for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
622 for (ncp = LIST_FIRST(ncpp); ncp != 0; ncp = nnp) {
623 nnp = LIST_NEXT(ncp, nc_hash);
624 if (ncp->nc_dvp->v_mount == mp) {
625 LIST_REMOVE(ncp, nc_hash);
626 LIST_INSERT_HEAD(&mplist, ncp, nc_hash);
630 while (!LIST_EMPTY(&mplist))
631 cache_zap(LIST_FIRST(&mplist));
636 * Perform canonical checks and cache lookup and pass on to filesystem
637 * through the vop_cachedlookup only if needed.
642 struct vop_lookup_args /* {
644 struct vnode **a_vpp;
645 struct componentname *a_cnp;
650 struct vnode **vpp = ap->a_vpp;
651 struct componentname *cnp = ap->a_cnp;
652 struct ucred *cred = cnp->cn_cred;
653 int flags = cnp->cn_flags;
654 struct thread *td = cnp->cn_thread;
659 if (dvp->v_type != VDIR)
662 if ((flags & ISLASTCN) && (dvp->v_mount->mnt_flag & MNT_RDONLY) &&
663 (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME))
666 error = VOP_ACCESS(dvp, VEXEC, cred, td);
670 error = cache_lookup(dvp, vpp, cnp);
672 return (VOP_CACHEDLOOKUP(dvp, vpp, cnp));
679 #ifndef _SYS_SYSPROTO_H_
680 struct __getcwd_args {
687 * XXX All of these sysctls would probably be more productive dead.
689 static int disablecwd;
690 SYSCTL_INT(_debug, OID_AUTO, disablecwd, CTLFLAG_RW, &disablecwd, 0,
691 "Disable the getcwd syscall");
693 /* Implementation of the getcwd syscall */
697 struct __getcwd_args *uap;
700 return (kern___getcwd(td, uap->buf, UIO_USERSPACE, uap->buflen));
704 kern___getcwd(struct thread *td, u_char *buf, enum uio_seg bufseg, u_int buflen)
707 struct filedesc *fdp;
714 if (buflen > MAXPATHLEN)
717 tmpbuf = malloc(buflen, M_TEMP, M_WAITOK);
718 fdp = td->td_proc->p_fd;
721 error = vn_fullpath1(td, fdp->fd_cdir, fdp->fd_rdir, tmpbuf,
723 FILEDESC_UNLOCK(fdp);
727 if (bufseg == UIO_SYSSPACE)
728 bcopy(bp, buf, strlen(bp) + 1);
730 error = copyout(bp, buf, strlen(bp) + 1);
732 free(tmpbuf, M_TEMP);
737 * Thus begins the fullpath magic.
741 #define STATNODE(name) \
743 SYSCTL_UINT(_vfs_cache, OID_AUTO, name, CTLFLAG_RD, &name, 0, "")
745 static int disablefullpath;
746 SYSCTL_INT(_debug, OID_AUTO, disablefullpath, CTLFLAG_RW, &disablefullpath, 0,
747 "Disable the vn_fullpath function");
749 /* These count for kern___getcwd(), too. */
750 STATNODE(numfullpathcalls);
751 STATNODE(numfullpathfail1);
752 STATNODE(numfullpathfail2);
753 STATNODE(numfullpathfail4);
754 STATNODE(numfullpathfound);
757 * Retrieve the full filesystem path that correspond to a vnode from the name
758 * cache (if available)
761 vn_fullpath(struct thread *td, struct vnode *vn, char **retbuf, char **freebuf)
764 struct filedesc *fdp;
772 buf = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
773 fdp = td->td_proc->p_fd;
776 error = vn_fullpath1(td, vn, fdp->fd_rdir, buf, retbuf, MAXPATHLEN);
777 FILEDESC_UNLOCK(fdp);
788 * The magic behind kern___getcwd() and vn_fullpath().
791 vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
792 char *buf, char **retbuf, u_int buflen)
795 int error, i, slash_prefixed;
796 struct namecache *ncp;
798 mtx_assert(&Giant, MA_OWNED);
800 bp = buf + buflen - 1;
807 if (vp->v_type != VDIR) {
808 ncp = TAILQ_FIRST(&vp->v_cache_dst);
814 for (i = ncp->nc_nlen - 1; i >= 0 && bp > buf; i--)
815 *--bp = ncp->nc_name[i];
825 while (vp != rdir && vp != rootvnode) {
826 if (vp->v_vflag & VV_ROOT) {
827 if (vp->v_mount == NULL) { /* forced unmount */
831 vp = vp->v_mount->mnt_vnodecovered;
834 if (vp->v_dd == NULL) {
839 ncp = TAILQ_FIRST(&vp->v_cache_dst);
845 MPASS(ncp->nc_dvp == vp->v_dd);
846 for (i = ncp->nc_nlen - 1; i >= 0 && bp != buf; i--)
847 *--bp = ncp->nc_name[i];
861 if (!slash_prefixed) {