xref: /freebsd/sys/kern/vfs_cache.c (revision 195ebc7e9e4b129de810833791a19dfb4349d6a9)
1 /*-
2  * Copyright (c) 1989, 1993, 1995
3  *	The Regents of the University of California.  All rights reserved.
4  *
5  * This code is derived from software contributed to Berkeley by
6  * Poul-Henning Kamp of the FreeBSD Project.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
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.
19  *
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
30  * SUCH DAMAGE.
31  *
32  *	@(#)vfs_cache.c	8.5 (Berkeley) 3/22/95
33  */
34 
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
37 
38 #include "opt_kdtrace.h"
39 #include "opt_ktrace.h"
40 
41 #include <sys/param.h>
42 #include <sys/filedesc.h>
43 #include <sys/fnv_hash.h>
44 #include <sys/kernel.h>
45 #include <sys/lock.h>
46 #include <sys/malloc.h>
47 #include <sys/mount.h>
48 #include <sys/namei.h>
49 #include <sys/proc.h>
50 #include <sys/rwlock.h>
51 #include <sys/sdt.h>
52 #include <sys/syscallsubr.h>
53 #include <sys/sysctl.h>
54 #include <sys/sysproto.h>
55 #include <sys/systm.h>
56 #include <sys/vnode.h>
57 #ifdef KTRACE
58 #include <sys/ktrace.h>
59 #endif
60 
61 #include <vm/uma.h>
62 
63 SDT_PROVIDER_DECLARE(vfs);
64 SDT_PROBE_DEFINE3(vfs, namecache, enter, done, "struct vnode *", "char *",
65     "struct vnode *");
66 SDT_PROBE_DEFINE2(vfs, namecache, enter_negative, done, "struct vnode *",
67     "char *");
68 SDT_PROBE_DEFINE1(vfs, namecache, fullpath, entry, "struct vnode *");
69 SDT_PROBE_DEFINE3(vfs, namecache, fullpath, hit, "struct vnode *",
70     "struct char *", "struct vnode *");
71 SDT_PROBE_DEFINE1(vfs, namecache, fullpath, miss, "struct vnode *");
72 SDT_PROBE_DEFINE3(vfs, namecache, fullpath, return, "int", "struct vnode *",
73     "struct char *");
74 SDT_PROBE_DEFINE3(vfs, namecache, lookup, hit, "struct vnode *", "char *",
75     "struct vnode *");
76 SDT_PROBE_DEFINE2(vfs, namecache, lookup, hit_negative, "struct vnode *",
77     "char *");
78 SDT_PROBE_DEFINE2(vfs, namecache, lookup, miss, "struct vnode *",
79     "char *");
80 SDT_PROBE_DEFINE1(vfs, namecache, purge, done, "struct vnode *");
81 SDT_PROBE_DEFINE1(vfs, namecache, purge_negative, done, "struct vnode *");
82 SDT_PROBE_DEFINE1(vfs, namecache, purgevfs, done, "struct mount *");
83 SDT_PROBE_DEFINE3(vfs, namecache, zap, done, "struct vnode *", "char *",
84     "struct vnode *");
85 SDT_PROBE_DEFINE2(vfs, namecache, zap_negative, done, "struct vnode *",
86     "char *");
87 
88 /*
89  * This structure describes the elements in the cache of recent
90  * names looked up by namei.
91  */
92 
93 struct	namecache {
94 	LIST_ENTRY(namecache) nc_hash;	/* hash chain */
95 	LIST_ENTRY(namecache) nc_src;	/* source vnode list */
96 	TAILQ_ENTRY(namecache) nc_dst;	/* destination vnode list */
97 	struct	vnode *nc_dvp;		/* vnode of parent of name */
98 	struct	vnode *nc_vp;		/* vnode the name refers to */
99 	u_char	nc_flag;		/* flag bits */
100 	u_char	nc_nlen;		/* length of name */
101 	char	nc_name[0];		/* segment name + nul */
102 };
103 
104 /*
105  * Name caching works as follows:
106  *
107  * Names found by directory scans are retained in a cache
108  * for future reference.  It is managed LRU, so frequently
109  * used names will hang around.  Cache is indexed by hash value
110  * obtained from (vp, name) where vp refers to the directory
111  * containing name.
112  *
113  * If it is a "negative" entry, (i.e. for a name that is known NOT to
114  * exist) the vnode pointer will be NULL.
115  *
116  * Upon reaching the last segment of a path, if the reference
117  * is for DELETE, or NOCACHE is set (rewrite), and the
118  * name is located in the cache, it will be dropped.
119  */
120 
121 /*
122  * Structures associated with name cacheing.
123  */
124 #define NCHHASH(hash) \
125 	(&nchashtbl[(hash) & nchash])
126 static LIST_HEAD(nchashhead, namecache) *nchashtbl;	/* Hash Table */
127 static TAILQ_HEAD(, namecache) ncneg;	/* Hash Table */
128 static u_long	nchash;			/* size of hash table */
129 SYSCTL_ULONG(_debug, OID_AUTO, nchash, CTLFLAG_RD, &nchash, 0, "");
130 static u_long	ncnegfactor = 16;	/* ratio of negative entries */
131 SYSCTL_ULONG(_debug, OID_AUTO, ncnegfactor, CTLFLAG_RW, &ncnegfactor, 0, "");
132 static u_long	numneg;			/* number of cache entries allocated */
133 SYSCTL_ULONG(_debug, OID_AUTO, numneg, CTLFLAG_RD, &numneg, 0, "");
134 static u_long	numcache;		/* number of cache entries allocated */
135 SYSCTL_ULONG(_debug, OID_AUTO, numcache, CTLFLAG_RD, &numcache, 0, "");
136 static u_long	numcachehv;		/* number of cache entries with vnodes held */
137 SYSCTL_ULONG(_debug, OID_AUTO, numcachehv, CTLFLAG_RD, &numcachehv, 0, "");
138 #if 0
139 static u_long	numcachepl;		/* number of cache purge for leaf entries */
140 SYSCTL_ULONG(_debug, OID_AUTO, numcachepl, CTLFLAG_RD, &numcachepl, 0, "");
141 #endif
142 struct	nchstats nchstats;		/* cache effectiveness statistics */
143 
144 static struct rwlock cache_lock;
145 RW_SYSINIT(vfscache, &cache_lock, "Name Cache");
146 
147 #define	CACHE_UPGRADE_LOCK()	rw_try_upgrade(&cache_lock)
148 #define	CACHE_RLOCK()		rw_rlock(&cache_lock)
149 #define	CACHE_RUNLOCK()		rw_runlock(&cache_lock)
150 #define	CACHE_WLOCK()		rw_wlock(&cache_lock)
151 #define	CACHE_WUNLOCK()		rw_wunlock(&cache_lock)
152 
153 /*
154  * UMA zones for the VFS cache.
155  *
156  * The small cache is used for entries with short names, which are the
157  * most common.  The large cache is used for entries which are too big to
158  * fit in the small cache.
159  */
160 static uma_zone_t cache_zone_small;
161 static uma_zone_t cache_zone_large;
162 
163 #define	CACHE_PATH_CUTOFF	35
164 #define	CACHE_ZONE_SMALL	(sizeof(struct namecache) + CACHE_PATH_CUTOFF \
165 				    + 1)
166 #define	CACHE_ZONE_LARGE	(sizeof(struct namecache) + NAME_MAX + 1)
167 
168 #define cache_alloc(len)	uma_zalloc(((len) <= CACHE_PATH_CUTOFF) ? \
169 	cache_zone_small : cache_zone_large, M_WAITOK)
170 #define cache_free(ncp)		do { \
171 	if (ncp != NULL) \
172 		uma_zfree(((ncp)->nc_nlen <= CACHE_PATH_CUTOFF) ? \
173 		    cache_zone_small : cache_zone_large, (ncp)); \
174 } while (0)
175 
176 static int	doingcache = 1;		/* 1 => enable the cache */
177 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, "");
178 
179 /* Export size information to userland */
180 SYSCTL_INT(_debug_sizeof, OID_AUTO, namecache, CTLFLAG_RD, 0,
181 	sizeof(struct namecache), "");
182 
183 /*
184  * The new name cache statistics
185  */
186 static SYSCTL_NODE(_vfs, OID_AUTO, cache, CTLFLAG_RW, 0, "Name cache statistics");
187 #define STATNODE(mode, name, var) \
188 	SYSCTL_ULONG(_vfs_cache, OID_AUTO, name, mode, var, 0, "");
189 STATNODE(CTLFLAG_RD, numneg, &numneg);
190 STATNODE(CTLFLAG_RD, numcache, &numcache);
191 static u_long numcalls; STATNODE(CTLFLAG_RD, numcalls, &numcalls);
192 static u_long dothits; STATNODE(CTLFLAG_RD, dothits, &dothits);
193 static u_long dotdothits; STATNODE(CTLFLAG_RD, dotdothits, &dotdothits);
194 static u_long numchecks; STATNODE(CTLFLAG_RD, numchecks, &numchecks);
195 static u_long nummiss; STATNODE(CTLFLAG_RD, nummiss, &nummiss);
196 static u_long nummisszap; STATNODE(CTLFLAG_RD, nummisszap, &nummisszap);
197 static u_long numposzaps; STATNODE(CTLFLAG_RD, numposzaps, &numposzaps);
198 static u_long numposhits; STATNODE(CTLFLAG_RD, numposhits, &numposhits);
199 static u_long numnegzaps; STATNODE(CTLFLAG_RD, numnegzaps, &numnegzaps);
200 static u_long numneghits; STATNODE(CTLFLAG_RD, numneghits, &numneghits);
201 static u_long numupgrades; STATNODE(CTLFLAG_RD, numupgrades, &numupgrades);
202 
203 SYSCTL_OPAQUE(_vfs_cache, OID_AUTO, nchstats, CTLFLAG_RD | CTLFLAG_MPSAFE,
204 	&nchstats, sizeof(nchstats), "LU", "VFS cache effectiveness statistics");
205 
206 
207 
208 static void cache_zap(struct namecache *ncp);
209 static int vn_vptocnp_locked(struct vnode **vp, char *buf, u_int *buflen);
210 static int vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
211     char *buf, char **retbuf, u_int buflen);
212 
213 static MALLOC_DEFINE(M_VFSCACHE, "vfscache", "VFS name cache entries");
214 
215 /*
216  * Flags in namecache.nc_flag
217  */
218 #define NCF_WHITE	0x01
219 #define NCF_ISDOTDOT	0x02
220 
221 #ifdef DIAGNOSTIC
222 /*
223  * Grab an atomic snapshot of the name cache hash chain lengths
224  */
225 SYSCTL_NODE(_debug, OID_AUTO, hashstat, CTLFLAG_RW, NULL, "hash table stats");
226 
227 static int
228 sysctl_debug_hashstat_rawnchash(SYSCTL_HANDLER_ARGS)
229 {
230 	int error;
231 	struct nchashhead *ncpp;
232 	struct namecache *ncp;
233 	int n_nchash;
234 	int count;
235 
236 	n_nchash = nchash + 1;	/* nchash is max index, not count */
237 	if (!req->oldptr)
238 		return SYSCTL_OUT(req, 0, n_nchash * sizeof(int));
239 
240 	/* Scan hash tables for applicable entries */
241 	for (ncpp = nchashtbl; n_nchash > 0; n_nchash--, ncpp++) {
242 		CACHE_RLOCK();
243 		count = 0;
244 		LIST_FOREACH(ncp, ncpp, nc_hash) {
245 			count++;
246 		}
247 		CACHE_RUNLOCK();
248 		error = SYSCTL_OUT(req, &count, sizeof(count));
249 		if (error)
250 			return (error);
251 	}
252 	return (0);
253 }
254 SYSCTL_PROC(_debug_hashstat, OID_AUTO, rawnchash, CTLTYPE_INT|CTLFLAG_RD|
255 	CTLFLAG_MPSAFE, 0, 0, sysctl_debug_hashstat_rawnchash, "S,int",
256 	"nchash chain lengths");
257 
258 static int
259 sysctl_debug_hashstat_nchash(SYSCTL_HANDLER_ARGS)
260 {
261 	int error;
262 	struct nchashhead *ncpp;
263 	struct namecache *ncp;
264 	int n_nchash;
265 	int count, maxlength, used, pct;
266 
267 	if (!req->oldptr)
268 		return SYSCTL_OUT(req, 0, 4 * sizeof(int));
269 
270 	n_nchash = nchash + 1;	/* nchash is max index, not count */
271 	used = 0;
272 	maxlength = 0;
273 
274 	/* Scan hash tables for applicable entries */
275 	for (ncpp = nchashtbl; n_nchash > 0; n_nchash--, ncpp++) {
276 		count = 0;
277 		CACHE_RLOCK();
278 		LIST_FOREACH(ncp, ncpp, nc_hash) {
279 			count++;
280 		}
281 		CACHE_RUNLOCK();
282 		if (count)
283 			used++;
284 		if (maxlength < count)
285 			maxlength = count;
286 	}
287 	n_nchash = nchash + 1;
288 	pct = (used * 100 * 100) / n_nchash;
289 	error = SYSCTL_OUT(req, &n_nchash, sizeof(n_nchash));
290 	if (error)
291 		return (error);
292 	error = SYSCTL_OUT(req, &used, sizeof(used));
293 	if (error)
294 		return (error);
295 	error = SYSCTL_OUT(req, &maxlength, sizeof(maxlength));
296 	if (error)
297 		return (error);
298 	error = SYSCTL_OUT(req, &pct, sizeof(pct));
299 	if (error)
300 		return (error);
301 	return (0);
302 }
303 SYSCTL_PROC(_debug_hashstat, OID_AUTO, nchash, CTLTYPE_INT|CTLFLAG_RD|
304 	CTLFLAG_MPSAFE, 0, 0, sysctl_debug_hashstat_nchash, "I",
305 	"nchash chain lengths");
306 #endif
307 
308 /*
309  * cache_zap():
310  *
311  *   Removes a namecache entry from cache, whether it contains an actual
312  *   pointer to a vnode or if it is just a negative cache entry.
313  */
314 static void
315 cache_zap(ncp)
316 	struct namecache *ncp;
317 {
318 	struct vnode *vp;
319 
320 	rw_assert(&cache_lock, RA_WLOCKED);
321 	CTR2(KTR_VFS, "cache_zap(%p) vp %p", ncp, ncp->nc_vp);
322 #ifdef KDTRACE_HOOKS
323 	if (ncp->nc_vp != NULL) {
324 		SDT_PROBE(vfs, namecache, zap, done, ncp->nc_dvp,
325 		    ncp->nc_name, ncp->nc_vp, 0, 0);
326 	} else {
327 		SDT_PROBE(vfs, namecache, zap_negative, done, ncp->nc_dvp,
328 		    ncp->nc_name, 0, 0, 0);
329 	}
330 #endif
331 	vp = NULL;
332 	LIST_REMOVE(ncp, nc_hash);
333 	if (ncp->nc_flag & NCF_ISDOTDOT) {
334 		if (ncp == ncp->nc_dvp->v_cache_dd)
335 			ncp->nc_dvp->v_cache_dd = NULL;
336 	} else {
337 		LIST_REMOVE(ncp, nc_src);
338 		if (LIST_EMPTY(&ncp->nc_dvp->v_cache_src)) {
339 			vp = ncp->nc_dvp;
340 			numcachehv--;
341 		}
342 	}
343 	if (ncp->nc_vp) {
344 		TAILQ_REMOVE(&ncp->nc_vp->v_cache_dst, ncp, nc_dst);
345 		if (ncp == ncp->nc_vp->v_cache_dd)
346 			ncp->nc_vp->v_cache_dd = NULL;
347 	} else {
348 		TAILQ_REMOVE(&ncneg, ncp, nc_dst);
349 		numneg--;
350 	}
351 	numcache--;
352 	cache_free(ncp);
353 	if (vp)
354 		vdrop(vp);
355 }
356 
357 /*
358  * Lookup an entry in the cache
359  *
360  * Lookup is called with dvp pointing to the directory to search,
361  * cnp pointing to the name of the entry being sought. If the lookup
362  * succeeds, the vnode is returned in *vpp, and a status of -1 is
363  * returned. If the lookup determines that the name does not exist
364  * (negative cacheing), a status of ENOENT is returned. If the lookup
365  * fails, a status of zero is returned.  If the directory vnode is
366  * recycled out from under us due to a forced unmount, a status of
367  * ENOENT is returned.
368  *
369  * vpp is locked and ref'd on return.  If we're looking up DOTDOT, dvp is
370  * unlocked.  If we're looking up . an extra ref is taken, but the lock is
371  * not recursively acquired.
372  */
373 
374 int
375 cache_lookup(dvp, vpp, cnp)
376 	struct vnode *dvp;
377 	struct vnode **vpp;
378 	struct componentname *cnp;
379 {
380 	struct namecache *ncp;
381 	u_int32_t hash;
382 	int error, ltype, wlocked;
383 
384 	if (!doingcache) {
385 		cnp->cn_flags &= ~MAKEENTRY;
386 		return (0);
387 	}
388 retry:
389 	CACHE_RLOCK();
390 	wlocked = 0;
391 	numcalls++;
392 	error = 0;
393 
394 retry_wlocked:
395 	if (cnp->cn_nameptr[0] == '.') {
396 		if (cnp->cn_namelen == 1) {
397 			*vpp = dvp;
398 			CTR2(KTR_VFS, "cache_lookup(%p, %s) found via .",
399 			    dvp, cnp->cn_nameptr);
400 			dothits++;
401 			SDT_PROBE(vfs, namecache, lookup, hit, dvp, ".",
402 			    *vpp, 0, 0);
403 			goto success;
404 		}
405 		if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
406 			dotdothits++;
407 			if (dvp->v_cache_dd == NULL) {
408 				SDT_PROBE(vfs, namecache, lookup, miss, dvp,
409 				    "..", NULL, 0, 0);
410 				goto unlock;
411 			}
412 			if ((cnp->cn_flags & MAKEENTRY) == 0) {
413 				if (!wlocked && !CACHE_UPGRADE_LOCK())
414 					goto wlock;
415 				if (dvp->v_cache_dd->nc_flag & NCF_ISDOTDOT)
416 					cache_zap(dvp->v_cache_dd);
417 				dvp->v_cache_dd = NULL;
418 				goto unlock;
419 			}
420 			if (dvp->v_cache_dd->nc_flag & NCF_ISDOTDOT)
421 				*vpp = dvp->v_cache_dd->nc_vp;
422 			else
423 				*vpp = dvp->v_cache_dd->nc_dvp;
424 			/* Return failure if negative entry was found. */
425 			if (*vpp == NULL) {
426 				ncp = dvp->v_cache_dd;
427 				goto negative_success;
428 			}
429 			CTR3(KTR_VFS, "cache_lookup(%p, %s) found %p via ..",
430 			    dvp, cnp->cn_nameptr, *vpp);
431 			SDT_PROBE(vfs, namecache, lookup, hit, dvp, "..",
432 			    *vpp, 0, 0);
433 			goto success;
434 		}
435 	}
436 
437 	hash = fnv_32_buf(cnp->cn_nameptr, cnp->cn_namelen, FNV1_32_INIT);
438 	hash = fnv_32_buf(&dvp, sizeof(dvp), hash);
439 	LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
440 		numchecks++;
441 		if (ncp->nc_dvp == dvp && ncp->nc_nlen == cnp->cn_namelen &&
442 		    !bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen))
443 			break;
444 	}
445 
446 	/* We failed to find an entry */
447 	if (ncp == NULL) {
448 		SDT_PROBE(vfs, namecache, lookup, miss, dvp, cnp->cn_nameptr,
449 		    NULL, 0, 0);
450 		if ((cnp->cn_flags & MAKEENTRY) == 0) {
451 			nummisszap++;
452 		} else {
453 			nummiss++;
454 		}
455 		nchstats.ncs_miss++;
456 		goto unlock;
457 	}
458 
459 	/* We don't want to have an entry, so dump it */
460 	if ((cnp->cn_flags & MAKEENTRY) == 0) {
461 		numposzaps++;
462 		nchstats.ncs_badhits++;
463 		if (!wlocked && !CACHE_UPGRADE_LOCK())
464 			goto wlock;
465 		cache_zap(ncp);
466 		CACHE_WUNLOCK();
467 		return (0);
468 	}
469 
470 	/* We found a "positive" match, return the vnode */
471 	if (ncp->nc_vp) {
472 		numposhits++;
473 		nchstats.ncs_goodhits++;
474 		*vpp = ncp->nc_vp;
475 		CTR4(KTR_VFS, "cache_lookup(%p, %s) found %p via ncp %p",
476 		    dvp, cnp->cn_nameptr, *vpp, ncp);
477 		SDT_PROBE(vfs, namecache, lookup, hit, dvp, ncp->nc_name,
478 		    *vpp, 0, 0);
479 		goto success;
480 	}
481 
482 negative_success:
483 	/* We found a negative match, and want to create it, so purge */
484 	if (cnp->cn_nameiop == CREATE) {
485 		numnegzaps++;
486 		nchstats.ncs_badhits++;
487 		if (!wlocked && !CACHE_UPGRADE_LOCK())
488 			goto wlock;
489 		cache_zap(ncp);
490 		CACHE_WUNLOCK();
491 		return (0);
492 	}
493 
494 	if (!wlocked && !CACHE_UPGRADE_LOCK())
495 		goto wlock;
496 	numneghits++;
497 	/*
498 	 * We found a "negative" match, so we shift it to the end of
499 	 * the "negative" cache entries queue to satisfy LRU.  Also,
500 	 * check to see if the entry is a whiteout; indicate this to
501 	 * the componentname, if so.
502 	 */
503 	TAILQ_REMOVE(&ncneg, ncp, nc_dst);
504 	TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
505 	nchstats.ncs_neghits++;
506 	if (ncp->nc_flag & NCF_WHITE)
507 		cnp->cn_flags |= ISWHITEOUT;
508 	SDT_PROBE(vfs, namecache, lookup, hit_negative, dvp, ncp->nc_name,
509 	    0, 0, 0);
510 	CACHE_WUNLOCK();
511 	return (ENOENT);
512 
513 wlock:
514 	/*
515 	 * We need to update the cache after our lookup, so upgrade to
516 	 * a write lock and retry the operation.
517 	 */
518 	CACHE_RUNLOCK();
519 	CACHE_WLOCK();
520 	numupgrades++;
521 	wlocked = 1;
522 	goto retry_wlocked;
523 
524 success:
525 	/*
526 	 * On success we return a locked and ref'd vnode as per the lookup
527 	 * protocol.
528 	 */
529 	if (dvp == *vpp) {   /* lookup on "." */
530 		VREF(*vpp);
531 		if (wlocked)
532 			CACHE_WUNLOCK();
533 		else
534 			CACHE_RUNLOCK();
535 		/*
536 		 * When we lookup "." we still can be asked to lock it
537 		 * differently...
538 		 */
539 		ltype = cnp->cn_lkflags & LK_TYPE_MASK;
540 		if (ltype != VOP_ISLOCKED(*vpp)) {
541 			if (ltype == LK_EXCLUSIVE) {
542 				vn_lock(*vpp, LK_UPGRADE | LK_RETRY);
543 				if ((*vpp)->v_iflag & VI_DOOMED) {
544 					/* forced unmount */
545 					vrele(*vpp);
546 					*vpp = NULL;
547 					return (ENOENT);
548 				}
549 			} else
550 				vn_lock(*vpp, LK_DOWNGRADE | LK_RETRY);
551 		}
552 		return (-1);
553 	}
554 	ltype = 0;	/* silence gcc warning */
555 	if (cnp->cn_flags & ISDOTDOT) {
556 		ltype = VOP_ISLOCKED(dvp);
557 		VOP_UNLOCK(dvp, 0);
558 	}
559 	VI_LOCK(*vpp);
560 	if (wlocked)
561 		CACHE_WUNLOCK();
562 	else
563 		CACHE_RUNLOCK();
564 	error = vget(*vpp, cnp->cn_lkflags | LK_INTERLOCK, cnp->cn_thread);
565 	if (cnp->cn_flags & ISDOTDOT) {
566 		vn_lock(dvp, ltype | LK_RETRY);
567 		if (dvp->v_iflag & VI_DOOMED) {
568 			if (error == 0)
569 				vput(*vpp);
570 			*vpp = NULL;
571 			return (ENOENT);
572 		}
573 	}
574 	if (error) {
575 		*vpp = NULL;
576 		goto retry;
577 	}
578 	if ((cnp->cn_flags & ISLASTCN) &&
579 	    (cnp->cn_lkflags & LK_TYPE_MASK) == LK_EXCLUSIVE) {
580 		ASSERT_VOP_ELOCKED(*vpp, "cache_lookup");
581 	}
582 	return (-1);
583 
584 unlock:
585 	if (wlocked)
586 		CACHE_WUNLOCK();
587 	else
588 		CACHE_RUNLOCK();
589 	return (0);
590 }
591 
592 /*
593  * Add an entry to the cache.
594  */
595 void
596 cache_enter(dvp, vp, cnp)
597 	struct vnode *dvp;
598 	struct vnode *vp;
599 	struct componentname *cnp;
600 {
601 	struct namecache *ncp, *n2;
602 	struct nchashhead *ncpp;
603 	u_int32_t hash;
604 	int flag;
605 	int hold;
606 	int zap;
607 	int len;
608 
609 	CTR3(KTR_VFS, "cache_enter(%p, %p, %s)", dvp, vp, cnp->cn_nameptr);
610 	VNASSERT(vp == NULL || (vp->v_iflag & VI_DOOMED) == 0, vp,
611 	    ("cahe_enter: Adding a doomed vnode"));
612 
613 	if (!doingcache)
614 		return;
615 
616 	/*
617 	 * Avoid blowout in namecache entries.
618 	 */
619 	if (numcache >= desiredvnodes * 2)
620 		return;
621 
622 	flag = 0;
623 	if (cnp->cn_nameptr[0] == '.') {
624 		if (cnp->cn_namelen == 1)
625 			return;
626 		if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
627 			CACHE_WLOCK();
628 			/*
629 			 * If dotdot entry already exists, just retarget it
630 			 * to new parent vnode, otherwise continue with new
631 			 * namecache entry allocation.
632 			 */
633 			if ((ncp = dvp->v_cache_dd) != NULL &&
634 			    ncp->nc_flag & NCF_ISDOTDOT) {
635 				KASSERT(ncp->nc_dvp == dvp,
636 				    ("wrong isdotdot parent"));
637 				if (ncp->nc_vp != NULL)
638 					TAILQ_REMOVE(&ncp->nc_vp->v_cache_dst,
639 					    ncp, nc_dst);
640 				else
641 					TAILQ_REMOVE(&ncneg, ncp, nc_dst);
642 				if (vp != NULL)
643 					TAILQ_INSERT_HEAD(&vp->v_cache_dst,
644 					    ncp, nc_dst);
645 				else
646 					TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
647 				ncp->nc_vp = vp;
648 				CACHE_WUNLOCK();
649 				return;
650 			}
651 			dvp->v_cache_dd = NULL;
652 			SDT_PROBE(vfs, namecache, enter, done, dvp, "..", vp,
653 			    0, 0);
654 			CACHE_WUNLOCK();
655 			flag = NCF_ISDOTDOT;
656 		}
657 	}
658 
659 	hold = 0;
660 	zap = 0;
661 
662 	/*
663 	 * Calculate the hash key and setup as much of the new
664 	 * namecache entry as possible before acquiring the lock.
665 	 */
666 	ncp = cache_alloc(cnp->cn_namelen);
667 	ncp->nc_vp = vp;
668 	ncp->nc_dvp = dvp;
669 	ncp->nc_flag = flag;
670 	len = ncp->nc_nlen = cnp->cn_namelen;
671 	hash = fnv_32_buf(cnp->cn_nameptr, len, FNV1_32_INIT);
672 	strlcpy(ncp->nc_name, cnp->cn_nameptr, len + 1);
673 	hash = fnv_32_buf(&dvp, sizeof(dvp), hash);
674 	CACHE_WLOCK();
675 
676 	/*
677 	 * See if this vnode or negative entry is already in the cache
678 	 * with this name.  This can happen with concurrent lookups of
679 	 * the same path name.
680 	 */
681 	ncpp = NCHHASH(hash);
682 	LIST_FOREACH(n2, ncpp, nc_hash) {
683 		if (n2->nc_dvp == dvp &&
684 		    n2->nc_nlen == cnp->cn_namelen &&
685 		    !bcmp(n2->nc_name, cnp->cn_nameptr, n2->nc_nlen)) {
686 			CACHE_WUNLOCK();
687 			cache_free(ncp);
688 			return;
689 		}
690 	}
691 
692 	if (flag == NCF_ISDOTDOT) {
693 		/*
694 		 * See if we are trying to add .. entry, but some other lookup
695 		 * has populated v_cache_dd pointer already.
696 		 */
697 		if (dvp->v_cache_dd != NULL) {
698 		    CACHE_WUNLOCK();
699 		    cache_free(ncp);
700 		    return;
701 		}
702 		KASSERT(vp == NULL || vp->v_type == VDIR,
703 		    ("wrong vnode type %p", vp));
704 		dvp->v_cache_dd = ncp;
705 	}
706 
707 	numcache++;
708 	if (!vp) {
709 		numneg++;
710 		if (cnp->cn_flags & ISWHITEOUT)
711 			ncp->nc_flag |= NCF_WHITE;
712 	} else if (vp->v_type == VDIR) {
713 		if (flag != NCF_ISDOTDOT) {
714 			if ((n2 = vp->v_cache_dd) != NULL &&
715 			    (n2->nc_flag & NCF_ISDOTDOT) != 0)
716 				cache_zap(n2);
717 			vp->v_cache_dd = ncp;
718 		}
719 	} else {
720 		vp->v_cache_dd = NULL;
721 	}
722 
723 	/*
724 	 * Insert the new namecache entry into the appropriate chain
725 	 * within the cache entries table.
726 	 */
727 	LIST_INSERT_HEAD(ncpp, ncp, nc_hash);
728 	if (flag != NCF_ISDOTDOT) {
729 		if (LIST_EMPTY(&dvp->v_cache_src)) {
730 			hold = 1;
731 			numcachehv++;
732 		}
733 		LIST_INSERT_HEAD(&dvp->v_cache_src, ncp, nc_src);
734 	}
735 
736 	/*
737 	 * If the entry is "negative", we place it into the
738 	 * "negative" cache queue, otherwise, we place it into the
739 	 * destination vnode's cache entries queue.
740 	 */
741 	if (vp) {
742 		TAILQ_INSERT_HEAD(&vp->v_cache_dst, ncp, nc_dst);
743 		SDT_PROBE(vfs, namecache, enter, done, dvp, ncp->nc_name, vp,
744 		    0, 0);
745 	} else {
746 		TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
747 		SDT_PROBE(vfs, namecache, enter_negative, done, dvp,
748 		    ncp->nc_name, 0, 0, 0);
749 	}
750 	if (numneg * ncnegfactor > numcache) {
751 		ncp = TAILQ_FIRST(&ncneg);
752 		zap = 1;
753 	}
754 	if (hold)
755 		vhold(dvp);
756 	if (zap)
757 		cache_zap(ncp);
758 	CACHE_WUNLOCK();
759 }
760 
761 /*
762  * Name cache initialization, from vfs_init() when we are booting
763  */
764 static void
765 nchinit(void *dummy __unused)
766 {
767 
768 	TAILQ_INIT(&ncneg);
769 
770 	cache_zone_small = uma_zcreate("S VFS Cache", CACHE_ZONE_SMALL, NULL,
771 	    NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_ZINIT);
772 	cache_zone_large = uma_zcreate("L VFS Cache", CACHE_ZONE_LARGE, NULL,
773 	    NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_ZINIT);
774 
775 	nchashtbl = hashinit(desiredvnodes * 2, M_VFSCACHE, &nchash);
776 }
777 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nchinit, NULL);
778 
779 
780 /*
781  * Invalidate all entries to a particular vnode.
782  */
783 void
784 cache_purge(vp)
785 	struct vnode *vp;
786 {
787 
788 	CTR1(KTR_VFS, "cache_purge(%p)", vp);
789 	SDT_PROBE(vfs, namecache, purge, done, vp, 0, 0, 0, 0);
790 	CACHE_WLOCK();
791 	while (!LIST_EMPTY(&vp->v_cache_src))
792 		cache_zap(LIST_FIRST(&vp->v_cache_src));
793 	while (!TAILQ_EMPTY(&vp->v_cache_dst))
794 		cache_zap(TAILQ_FIRST(&vp->v_cache_dst));
795 	if (vp->v_cache_dd != NULL) {
796 		KASSERT(vp->v_cache_dd->nc_flag & NCF_ISDOTDOT,
797 		   ("lost dotdot link"));
798 		cache_zap(vp->v_cache_dd);
799 	}
800 	KASSERT(vp->v_cache_dd == NULL, ("incomplete purge"));
801 	CACHE_WUNLOCK();
802 }
803 
804 /*
805  * Invalidate all negative entries for a particular directory vnode.
806  */
807 void
808 cache_purge_negative(vp)
809 	struct vnode *vp;
810 {
811 	struct namecache *cp, *ncp;
812 
813 	CTR1(KTR_VFS, "cache_purge_negative(%p)", vp);
814 	SDT_PROBE(vfs, namecache, purge_negative, done, vp, 0, 0, 0, 0);
815 	CACHE_WLOCK();
816 	LIST_FOREACH_SAFE(cp, &vp->v_cache_src, nc_src, ncp) {
817 		if (cp->nc_vp == NULL)
818 			cache_zap(cp);
819 	}
820 	CACHE_WUNLOCK();
821 }
822 
823 /*
824  * Flush all entries referencing a particular filesystem.
825  */
826 void
827 cache_purgevfs(mp)
828 	struct mount *mp;
829 {
830 	struct nchashhead *ncpp;
831 	struct namecache *ncp, *nnp;
832 
833 	/* Scan hash tables for applicable entries */
834 	SDT_PROBE(vfs, namecache, purgevfs, done, mp, 0, 0, 0, 0);
835 	CACHE_WLOCK();
836 	for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
837 		LIST_FOREACH_SAFE(ncp, ncpp, nc_hash, nnp) {
838 			if (ncp->nc_dvp->v_mount == mp)
839 				cache_zap(ncp);
840 		}
841 	}
842 	CACHE_WUNLOCK();
843 }
844 
845 /*
846  * Perform canonical checks and cache lookup and pass on to filesystem
847  * through the vop_cachedlookup only if needed.
848  */
849 
850 int
851 vfs_cache_lookup(ap)
852 	struct vop_lookup_args /* {
853 		struct vnode *a_dvp;
854 		struct vnode **a_vpp;
855 		struct componentname *a_cnp;
856 	} */ *ap;
857 {
858 	struct vnode *dvp;
859 	int error;
860 	struct vnode **vpp = ap->a_vpp;
861 	struct componentname *cnp = ap->a_cnp;
862 	struct ucred *cred = cnp->cn_cred;
863 	int flags = cnp->cn_flags;
864 	struct thread *td = cnp->cn_thread;
865 
866 	*vpp = NULL;
867 	dvp = ap->a_dvp;
868 
869 	if (dvp->v_type != VDIR)
870 		return (ENOTDIR);
871 
872 	if ((flags & ISLASTCN) && (dvp->v_mount->mnt_flag & MNT_RDONLY) &&
873 	    (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME))
874 		return (EROFS);
875 
876 	error = VOP_ACCESS(dvp, VEXEC, cred, td);
877 	if (error)
878 		return (error);
879 
880 	error = cache_lookup(dvp, vpp, cnp);
881 	if (error == 0)
882 		return (VOP_CACHEDLOOKUP(dvp, vpp, cnp));
883 	if (error == -1)
884 		return (0);
885 	return (error);
886 }
887 
888 
889 #ifndef _SYS_SYSPROTO_H_
890 struct  __getcwd_args {
891 	u_char	*buf;
892 	u_int	buflen;
893 };
894 #endif
895 
896 /*
897  * XXX All of these sysctls would probably be more productive dead.
898  */
899 static int disablecwd;
900 SYSCTL_INT(_debug, OID_AUTO, disablecwd, CTLFLAG_RW, &disablecwd, 0,
901    "Disable the getcwd syscall");
902 
903 /* Implementation of the getcwd syscall. */
904 int
905 __getcwd(td, uap)
906 	struct thread *td;
907 	struct __getcwd_args *uap;
908 {
909 
910 	return (kern___getcwd(td, uap->buf, UIO_USERSPACE, uap->buflen));
911 }
912 
913 int
914 kern___getcwd(struct thread *td, u_char *buf, enum uio_seg bufseg, u_int buflen)
915 {
916 	char *bp, *tmpbuf;
917 	struct filedesc *fdp;
918 	struct vnode *cdir, *rdir;
919 	int error, vfslocked;
920 
921 	if (disablecwd)
922 		return (ENODEV);
923 	if (buflen < 2)
924 		return (EINVAL);
925 	if (buflen > MAXPATHLEN)
926 		buflen = MAXPATHLEN;
927 
928 	tmpbuf = malloc(buflen, M_TEMP, M_WAITOK);
929 	fdp = td->td_proc->p_fd;
930 	FILEDESC_SLOCK(fdp);
931 	cdir = fdp->fd_cdir;
932 	VREF(cdir);
933 	rdir = fdp->fd_rdir;
934 	VREF(rdir);
935 	FILEDESC_SUNLOCK(fdp);
936 	error = vn_fullpath1(td, cdir, rdir, tmpbuf, &bp, buflen);
937 	vfslocked = VFS_LOCK_GIANT(rdir->v_mount);
938 	vrele(rdir);
939 	VFS_UNLOCK_GIANT(vfslocked);
940 	vfslocked = VFS_LOCK_GIANT(cdir->v_mount);
941 	vrele(cdir);
942 	VFS_UNLOCK_GIANT(vfslocked);
943 
944 	if (!error) {
945 		if (bufseg == UIO_SYSSPACE)
946 			bcopy(bp, buf, strlen(bp) + 1);
947 		else
948 			error = copyout(bp, buf, strlen(bp) + 1);
949 #ifdef KTRACE
950 	if (KTRPOINT(curthread, KTR_NAMEI))
951 		ktrnamei(bp);
952 #endif
953 	}
954 	free(tmpbuf, M_TEMP);
955 	return (error);
956 }
957 
958 /*
959  * Thus begins the fullpath magic.
960  */
961 
962 #undef STATNODE
963 #define STATNODE(name)							\
964 	static u_int name;						\
965 	SYSCTL_UINT(_vfs_cache, OID_AUTO, name, CTLFLAG_RD, &name, 0, "")
966 
967 static int disablefullpath;
968 SYSCTL_INT(_debug, OID_AUTO, disablefullpath, CTLFLAG_RW, &disablefullpath, 0,
969 	"Disable the vn_fullpath function");
970 
971 /* These count for kern___getcwd(), too. */
972 STATNODE(numfullpathcalls);
973 STATNODE(numfullpathfail1);
974 STATNODE(numfullpathfail2);
975 STATNODE(numfullpathfail4);
976 STATNODE(numfullpathfound);
977 
978 /*
979  * Retrieve the full filesystem path that correspond to a vnode from the name
980  * cache (if available)
981  */
982 int
983 vn_fullpath(struct thread *td, struct vnode *vn, char **retbuf, char **freebuf)
984 {
985 	char *buf;
986 	struct filedesc *fdp;
987 	struct vnode *rdir;
988 	int error, vfslocked;
989 
990 	if (disablefullpath)
991 		return (ENODEV);
992 	if (vn == NULL)
993 		return (EINVAL);
994 
995 	buf = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
996 	fdp = td->td_proc->p_fd;
997 	FILEDESC_SLOCK(fdp);
998 	rdir = fdp->fd_rdir;
999 	VREF(rdir);
1000 	FILEDESC_SUNLOCK(fdp);
1001 	error = vn_fullpath1(td, vn, rdir, buf, retbuf, MAXPATHLEN);
1002 	vfslocked = VFS_LOCK_GIANT(rdir->v_mount);
1003 	vrele(rdir);
1004 	VFS_UNLOCK_GIANT(vfslocked);
1005 
1006 	if (!error)
1007 		*freebuf = buf;
1008 	else
1009 		free(buf, M_TEMP);
1010 	return (error);
1011 }
1012 
1013 /*
1014  * This function is similar to vn_fullpath, but it attempts to lookup the
1015  * pathname relative to the global root mount point.  This is required for the
1016  * auditing sub-system, as audited pathnames must be absolute, relative to the
1017  * global root mount point.
1018  */
1019 int
1020 vn_fullpath_global(struct thread *td, struct vnode *vn,
1021     char **retbuf, char **freebuf)
1022 {
1023 	char *buf;
1024 	int error;
1025 
1026 	if (disablefullpath)
1027 		return (ENODEV);
1028 	if (vn == NULL)
1029 		return (EINVAL);
1030 	buf = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
1031 	error = vn_fullpath1(td, vn, rootvnode, buf, retbuf, MAXPATHLEN);
1032 	if (!error)
1033 		*freebuf = buf;
1034 	else
1035 		free(buf, M_TEMP);
1036 	return (error);
1037 }
1038 
1039 int
1040 vn_vptocnp(struct vnode **vp, char *buf, u_int *buflen)
1041 {
1042 	int error;
1043 
1044 	CACHE_RLOCK();
1045 	error = vn_vptocnp_locked(vp, buf, buflen);
1046 	if (error == 0) {
1047 		/*
1048 		 * vn_vptocnp_locked() dropped hold acquired by
1049 		 * VOP_VPTOCNP immediately after locking the
1050 		 * cache. Since we are going to drop the cache rlock,
1051 		 * re-hold the result.
1052 		 */
1053 		vhold(*vp);
1054 		CACHE_RUNLOCK();
1055 	}
1056 	return (error);
1057 }
1058 
1059 static int
1060 vn_vptocnp_locked(struct vnode **vp, char *buf, u_int *buflen)
1061 {
1062 	struct vnode *dvp;
1063 	struct namecache *ncp;
1064 	int error, vfslocked;
1065 
1066 	TAILQ_FOREACH(ncp, &((*vp)->v_cache_dst), nc_dst) {
1067 		if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
1068 			break;
1069 	}
1070 	if (ncp != NULL) {
1071 		if (*buflen < ncp->nc_nlen) {
1072 			CACHE_RUNLOCK();
1073 			numfullpathfail4++;
1074 			error = ENOMEM;
1075 			SDT_PROBE(vfs, namecache, fullpath, return, error,
1076 			    vp, NULL, 0, 0);
1077 			return (error);
1078 		}
1079 		*buflen -= ncp->nc_nlen;
1080 		memcpy(buf + *buflen, ncp->nc_name, ncp->nc_nlen);
1081 		SDT_PROBE(vfs, namecache, fullpath, hit, ncp->nc_dvp,
1082 		    ncp->nc_name, vp, 0, 0);
1083 		*vp = ncp->nc_dvp;
1084 		return (0);
1085 	}
1086 	SDT_PROBE(vfs, namecache, fullpath, miss, vp, 0, 0, 0, 0);
1087 
1088 	vhold(*vp);
1089 	CACHE_RUNLOCK();
1090 	vfslocked = VFS_LOCK_GIANT((*vp)->v_mount);
1091 	vn_lock(*vp, LK_SHARED | LK_RETRY);
1092 	error = VOP_VPTOCNP(*vp, &dvp, buf, buflen);
1093 	VOP_UNLOCK(*vp, 0);
1094 	vdrop(*vp);
1095 	VFS_UNLOCK_GIANT(vfslocked);
1096 	if (error) {
1097 		numfullpathfail2++;
1098 		SDT_PROBE(vfs, namecache, fullpath, return,  error, vp,
1099 		    NULL, 0, 0);
1100 		return (error);
1101 	}
1102 
1103 	*vp = dvp;
1104 	CACHE_RLOCK();
1105 	if ((*vp)->v_iflag & VI_DOOMED) {
1106 		/* forced unmount */
1107 		CACHE_RUNLOCK();
1108 		vdrop(*vp);
1109 		error = ENOENT;
1110 		SDT_PROBE(vfs, namecache, fullpath, return, error, vp,
1111 		    NULL, 0, 0);
1112 		return (error);
1113 	}
1114 	vdrop(*vp);
1115 
1116 	return (0);
1117 }
1118 
1119 /*
1120  * The magic behind kern___getcwd() and vn_fullpath().
1121  */
1122 static int
1123 vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
1124     char *buf, char **retbuf, u_int buflen)
1125 {
1126 	int error, slash_prefixed;
1127 #ifdef KDTRACE_HOOKS
1128 	struct vnode *startvp = vp;
1129 #endif
1130 
1131 	buflen--;
1132 	buf[buflen] = '\0';
1133 	error = 0;
1134 	slash_prefixed = 0;
1135 
1136 	SDT_PROBE(vfs, namecache, fullpath, entry, vp, 0, 0, 0, 0);
1137 	numfullpathcalls++;
1138 	CACHE_RLOCK();
1139 	if (vp->v_type != VDIR) {
1140 		error = vn_vptocnp_locked(&vp, buf, &buflen);
1141 		if (error)
1142 			return (error);
1143 		if (buflen == 0)
1144 			return (ENOMEM);
1145 		buf[--buflen] = '/';
1146 		slash_prefixed = 1;
1147 	}
1148 	while (vp != rdir && vp != rootvnode) {
1149 		if (vp->v_vflag & VV_ROOT) {
1150 			if (vp->v_iflag & VI_DOOMED) {	/* forced unmount */
1151 				CACHE_RUNLOCK();
1152 				error = ENOENT;
1153 				SDT_PROBE(vfs, namecache, fullpath, return,
1154 				    error, vp, NULL, 0, 0);
1155 				break;
1156 			}
1157 			vp = vp->v_mount->mnt_vnodecovered;
1158 			continue;
1159 		}
1160 		if (vp->v_type != VDIR) {
1161 			CACHE_RUNLOCK();
1162 			numfullpathfail1++;
1163 			error = ENOTDIR;
1164 			SDT_PROBE(vfs, namecache, fullpath, return,
1165 			    error, vp, NULL, 0, 0);
1166 			break;
1167 		}
1168 		error = vn_vptocnp_locked(&vp, buf, &buflen);
1169 		if (error)
1170 			break;
1171 		if (buflen == 0) {
1172 			error = ENOMEM;
1173 			SDT_PROBE(vfs, namecache, fullpath, return, error,
1174 			    startvp, NULL, 0, 0);
1175 			break;
1176 		}
1177 		buf[--buflen] = '/';
1178 		slash_prefixed = 1;
1179 	}
1180 	if (error)
1181 		return (error);
1182 	if (!slash_prefixed) {
1183 		if (buflen == 0) {
1184 			CACHE_RUNLOCK();
1185 			numfullpathfail4++;
1186 			SDT_PROBE(vfs, namecache, fullpath, return, ENOMEM,
1187 			    startvp, NULL, 0, 0);
1188 			return (ENOMEM);
1189 		}
1190 		buf[--buflen] = '/';
1191 	}
1192 	numfullpathfound++;
1193 	CACHE_RUNLOCK();
1194 
1195 	SDT_PROBE(vfs, namecache, fullpath, return, 0, startvp, buf + buflen,
1196 	    0, 0);
1197 	*retbuf = buf + buflen;
1198 	return (0);
1199 }
1200 
1201 int
1202 vn_commname(struct vnode *vp, char *buf, u_int buflen)
1203 {
1204 	struct namecache *ncp;
1205 	int l;
1206 
1207 	CACHE_RLOCK();
1208 	TAILQ_FOREACH(ncp, &vp->v_cache_dst, nc_dst)
1209 		if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
1210 			break;
1211 	if (ncp == NULL) {
1212 		CACHE_RUNLOCK();
1213 		return (ENOENT);
1214 	}
1215 	l = min(ncp->nc_nlen, buflen - 1);
1216 	memcpy(buf, ncp->nc_name, l);
1217 	CACHE_RUNLOCK();
1218 	buf[l] = '\0';
1219 	return (0);
1220 }
1221