1 /* $OpenBSD: vfs_cache.c,v 1.25 2007/06/21 12:05:14 pedro Exp $ */
2 /* $NetBSD: vfs_cache.c,v 1.13 1996/02/04 02:18:09 christos Exp $ */
3
4 /*
5 * Copyright (c) 1989, 1993
6 * The Regents of the University of California. All rights reserved.
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 * 3. 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 8.3 (Berkeley) 8/22/94
33 */
34
35 #include <sys/param.h>
36 #include <sys/systm.h>
37 #include <sys/time.h>
38 #include <sys/mount.h>
39 #include <sys/vnode.h>
40 #include <sys/namei.h>
41 #include <sys/errno.h>
42 #include <sys/malloc.h>
43 #include <sys/pool.h>
44 #include <sys/hash.h>
45
46 /*
47 * TODO: namecache access should really be locked.
48 */
49
50 /*
51 * Name caching works as follows:
52 *
53 * Names found by directory scans are retained in a cache
54 * for future reference. It is managed LRU, so frequently
55 * used names will hang around. Cache is indexed by hash value
56 * obtained from (vp, name) where vp refers to the directory
57 * containing name.
58 *
59 * For simplicity (and economy of storage), names longer than
60 * a maximum length of NCHNAMLEN are not cached; they occur
61 * infrequently in any case, and are almost never of interest.
62 *
63 * Upon reaching the last segment of a path, if the reference
64 * is for DELETE, or NOCACHE is set (rewrite), and the
65 * name is located in the cache, it will be dropped.
66 */
67
68 /*
69 * Structures associated with name caching.
70 */
71 LIST_HEAD(nchashhead, namecache) *nchashtbl;
72 u_long nchash; /* size of hash table - 1 */
73 long numcache; /* number of cache entries allocated */
74 TAILQ_HEAD(, namecache) nclruhead; /* LRU chain */
75 struct nchstats nchstats; /* cache effectiveness statistics */
76
77 LIST_HEAD(ncvhashhead, namecache) *ncvhashtbl;
78 u_long ncvhash; /* size of hash table - 1 */
79
80 #define NCHASH(dvp, cnp) \
81 hash32_buf(&(dvp)->v_id, sizeof((dvp)->v_id), (cnp)->cn_hash) & nchash
82
83 #define NCVHASH(vp) (vp)->v_id & ncvhash
84
85 int doingcache = 1; /* 1 => enable the cache */
86
87 struct pool nch_pool;
88
89 u_long nextvnodeid;
90
91 /*
92 * Look for a name in the cache. We don't do this if the segment name is
93 * long, simply so the cache can avoid holding long names (which would
94 * either waste space, or add greatly to the complexity).
95 *
96 * Lookup is called with ni_dvp pointing to the directory to search,
97 * ni_ptr pointing to the name of the entry being sought, ni_namelen
98 * tells the length of the name, and ni_hash contains a hash of
99 * the name. If the lookup succeeds, the vnode is returned in ni_vp
100 * and a status of 0 is returned. If the locking fails for whatever
101 * reason, the vnode is unlocked and the error is returned to caller.
102 * If the lookup determines that the name does not exist (negative caching),
103 * a status of ENOENT is returned. If the lookup fails, a status of -1
104 * is returned.
105 */
106 int
107 cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
108 {
109 struct namecache *ncp;
110 struct nchashhead *ncpp;
111 struct vnode *vp;
112 struct proc *p = curproc;
113 u_long vpid;
114 int error;
115
116 *vpp = NULL;
117
118 if (!doingcache) {
119 cnp->cn_flags &= ~MAKEENTRY;
120 return (-1);
121 }
122 if (cnp->cn_namelen > NCHNAMLEN) {
123 nchstats.ncs_long++;
124 cnp->cn_flags &= ~MAKEENTRY;
125 return (-1);
126 }
127
128 ncpp = &nchashtbl[NCHASH(dvp, cnp)];
129 LIST_FOREACH(ncp, ncpp, nc_hash) {
130 if (ncp->nc_dvp == dvp &&
131 ncp->nc_dvpid == dvp->v_id &&
132 ncp->nc_nlen == cnp->cn_namelen &&
133 !memcmp(ncp->nc_name, cnp->cn_nameptr, (u_int)ncp->nc_nlen))
134 break;
135 }
136 if (ncp == NULL) {
137 nchstats.ncs_miss++;
138 return (-1);
139 }
140 if ((cnp->cn_flags & MAKEENTRY) == 0) {
141 nchstats.ncs_badhits++;
142 goto remove;
143 } else if (ncp->nc_vp == NULL) {
144 if (cnp->cn_nameiop != CREATE ||
145 (cnp->cn_flags & ISLASTCN) == 0) {
146 nchstats.ncs_neghits++;
147 /*
148 * Move this slot to end of LRU chain,
149 * if not already there.
150 */
151 if (TAILQ_NEXT(ncp, nc_lru) != NULL) {
152 TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
153 TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
154 }
155 return (ENOENT);
156 } else {
157 nchstats.ncs_badhits++;
158 goto remove;
159 }
160 } else if (ncp->nc_vpid != ncp->nc_vp->v_id) {
161 nchstats.ncs_falsehits++;
162 goto remove;
163 }
164
165 vp = ncp->nc_vp;
166 vpid = vp->v_id;
167 if (vp == dvp) { /* lookup on "." */
168 VREF(dvp);
169 error = 0;
170 } else if (cnp->cn_flags & ISDOTDOT) {
171 VOP_UNLOCK(dvp, 0, p);
172 cnp->cn_flags |= PDIRUNLOCK;
173 error = vget(vp, LK_EXCLUSIVE, p);
174 /*
175 * If the above vget() succeeded and both LOCKPARENT and
176 * ISLASTCN is set, lock the directory vnode as well.
177 */
178 if (!error && (~cnp->cn_flags & (LOCKPARENT|ISLASTCN)) == 0) {
179 if ((error = vn_lock(dvp, LK_EXCLUSIVE, p)) != 0) {
180 vput(vp);
181 return (error);
182 }
183 cnp->cn_flags &= ~PDIRUNLOCK;
184 }
185 } else {
186 error = vget(vp, LK_EXCLUSIVE, p);
187 /*
188 * If the above vget() failed or either of LOCKPARENT or
189 * ISLASTCN is set, unlock the directory vnode.
190 */
191 if (error || (~cnp->cn_flags & (LOCKPARENT|ISLASTCN)) != 0) {
192 VOP_UNLOCK(dvp, 0, p);
193 cnp->cn_flags |= PDIRUNLOCK;
194 }
195 }
196
197 /*
198 * Check that the lock succeeded, and that the capability number did
199 * not change while we were waiting for the lock.
200 */
201 if (error || vpid != vp->v_id) {
202 if (!error) {
203 vput(vp);
204 nchstats.ncs_falsehits++;
205 } else
206 nchstats.ncs_badhits++;
207 /*
208 * The parent needs to be locked when we return to VOP_LOOKUP().
209 * The `.' case here should be extremely rare (if it can happen
210 * at all), so we don't bother optimizing out the unlock/relock.
211 */
212 if (vp == dvp || error ||
213 (~cnp->cn_flags & (LOCKPARENT|ISLASTCN)) != 0) {
214 if ((error = vn_lock(dvp, LK_EXCLUSIVE, p)) != 0)
215 return (error);
216 cnp->cn_flags &= ~PDIRUNLOCK;
217 }
218 return (-1);
219 }
220
221 nchstats.ncs_goodhits++;
222 /*
223 * Move this slot to end of LRU chain, if not already there.
224 */
225 if (TAILQ_NEXT(ncp, nc_lru) != NULL) {
226 TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
227 TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
228 }
229 *vpp = vp;
230 return (0);
231
232 remove:
233 /*
234 * Last component and we are renaming or deleting,
235 * the cache entry is invalid, or otherwise don't
236 * want cache entry to exist.
237 */
238 TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
239 LIST_REMOVE(ncp, nc_hash);
240 ncp->nc_hash.le_prev = NULL;
241
242 if (ncp->nc_vhash.le_prev != NULL) {
243 LIST_REMOVE(ncp, nc_vhash);
244 ncp->nc_vhash.le_prev = NULL;
245 }
246
247 pool_put(&nch_pool, ncp);
248 numcache--;
249 return (-1);
250 }
251
252 /*
253 * Scan cache looking for name of directory entry pointing at vp.
254 *
255 * Fill in dvpp.
256 *
257 * If bufp is non-NULL, also place the name in the buffer which starts
258 * at bufp, immediately before *bpp, and move bpp backwards to point
259 * at the start of it. (Yes, this is a little baroque, but it's done
260 * this way to cater to the whims of getcwd).
261 *
262 * Returns 0 on success, -1 on cache miss, positive errno on failure.
263 *
264 * TODO: should we return *dvpp locked?
265 */
266
267 int
268 cache_revlookup(struct vnode *vp, struct vnode **dvpp, char **bpp, char *bufp)
269 {
270 struct namecache *ncp;
271 struct vnode *dvp;
272 struct ncvhashhead *nvcpp;
273 char *bp;
274
275 if (!doingcache)
276 goto out;
277
278 nvcpp = &ncvhashtbl[NCVHASH(vp)];
279
280 LIST_FOREACH(ncp, nvcpp, nc_vhash) {
281 if (ncp->nc_vp == vp &&
282 ncp->nc_vpid == vp->v_id &&
283 (dvp = ncp->nc_dvp) != NULL &&
284 /* avoid pesky '.' entries.. */
285 dvp != vp && ncp->nc_dvpid == dvp->v_id) {
286
287 #ifdef DIAGNOSTIC
288 if (ncp->nc_nlen == 1 &&
289 ncp->nc_name[0] == '.')
290 panic("cache_revlookup: found entry for .");
291
292 if (ncp->nc_nlen == 2 &&
293 ncp->nc_name[0] == '.' &&
294 ncp->nc_name[1] == '.')
295 panic("cache_revlookup: found entry for ..");
296 #endif
297 nchstats.ncs_revhits++;
298
299 if (bufp != NULL) {
300 bp = *bpp;
301 bp -= ncp->nc_nlen;
302 if (bp <= bufp) {
303 *dvpp = NULL;
304 return (ERANGE);
305 }
306 memcpy(bp, ncp->nc_name, ncp->nc_nlen);
307 *bpp = bp;
308 }
309
310 *dvpp = dvp;
311
312 /*
313 * XXX: Should we vget() here to have more
314 * consistent semantics with cache_lookup()?
315 *
316 * For MP safety it might be necessary to do
317 * this here, while also protecting hash
318 * tables themselves to provide some sort of
319 * sane inter locking.
320 */
321 return (0);
322 }
323 }
324 nchstats.ncs_revmiss++;
325
326 out:
327 *dvpp = NULL;
328 return (-1);
329 }
330
331 /*
332 * Add an entry to the cache
333 */
334 void
335 cache_enter(struct vnode *dvp, struct vnode *vp, struct componentname *cnp)
336 {
337 struct namecache *ncp;
338 struct nchashhead *ncpp;
339 struct ncvhashhead *nvcpp;
340
341 if (!doingcache || cnp->cn_namelen > NCHNAMLEN)
342 return;
343
344 /*
345 * Free the cache slot at head of lru chain.
346 */
347 if (numcache < desiredvnodes) {
348 ncp = pool_get(&nch_pool, PR_WAITOK);
349 bzero((char *)ncp, sizeof *ncp);
350 numcache++;
351 } else if ((ncp = TAILQ_FIRST(&nclruhead)) != NULL) {
352 TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
353 if (ncp->nc_hash.le_prev != NULL) {
354 LIST_REMOVE(ncp, nc_hash);
355 ncp->nc_hash.le_prev = NULL;
356 }
357 if (ncp->nc_vhash.le_prev != NULL) {
358 LIST_REMOVE(ncp, nc_vhash);
359 ncp->nc_vhash.le_prev = NULL;
360 }
361 } else
362 return;
363 /* grab the vnode we just found */
364 ncp->nc_vp = vp;
365 if (vp)
366 ncp->nc_vpid = vp->v_id;
367 /* fill in cache info */
368 ncp->nc_dvp = dvp;
369 ncp->nc_dvpid = dvp->v_id;
370 ncp->nc_nlen = cnp->cn_namelen;
371 bcopy(cnp->cn_nameptr, ncp->nc_name, (unsigned)ncp->nc_nlen);
372 TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
373 ncpp = &nchashtbl[NCHASH(dvp, cnp)];
374 LIST_INSERT_HEAD(ncpp, ncp, nc_hash);
375
376 /*
377 * Create reverse-cache entries (used in getcwd) for
378 * directories.
379 */
380
381 ncp->nc_vhash.le_prev = NULL;
382 ncp->nc_vhash.le_next = NULL;
383
384 if (vp && vp != dvp && vp->v_type == VDIR &&
385 (ncp->nc_nlen > 2 ||
386 (ncp->nc_nlen > 1 && ncp->nc_name[1] != '.') ||
387 (ncp->nc_nlen > 0 && ncp->nc_name[0] != '.'))) {
388 nvcpp = &ncvhashtbl[NCVHASH(vp)];
389 LIST_INSERT_HEAD(nvcpp, ncp, nc_vhash);
390 }
391 }
392
393 /*
394 * Name cache initialization, from vfs_init() when we are booting
395 */
396 void
397 nchinit(void)
398 {
399
400 TAILQ_INIT(&nclruhead);
401 nchashtbl = hashinit(desiredvnodes, M_CACHE, M_WAITOK, &nchash);
402 ncvhashtbl = hashinit(desiredvnodes/8, M_CACHE, M_WAITOK, &ncvhash);
403 pool_init(&nch_pool, sizeof(struct namecache), 0, 0, 0, "nchpl",
404 &pool_allocator_nointr);
405 }
406
407 /*
408 * Cache flush, a particular vnode; called when a vnode is renamed to
409 * hide entries that would now be invalid
410 */
411 void
412 cache_purge(struct vnode *vp)
413 {
414 struct namecache *ncp;
415 struct nchashhead *ncpp;
416
417 vp->v_id = ++nextvnodeid;
418 if (nextvnodeid != 0)
419 return;
420 for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
421 LIST_FOREACH(ncp, ncpp, nc_hash) {
422 ncp->nc_vpid = 0;
423 ncp->nc_dvpid = 0;
424 }
425 }
426 vp->v_id = ++nextvnodeid;
427 }
428
429 /*
430 * Cache flush, a whole filesystem; called when filesys is umounted to
431 * remove entries that would now be invalid
432 */
433 void
434 cache_purgevfs(struct mount *mp)
435 {
436 struct namecache *ncp, *nxtcp;
437
438 for (ncp = TAILQ_FIRST(&nclruhead); ncp != TAILQ_END(&nclruhead);
439 ncp = nxtcp) {
440 nxtcp = TAILQ_NEXT(ncp, nc_lru);
441 if (ncp->nc_dvp == NULL || ncp->nc_dvp->v_mount != mp)
442 continue;
443 /* free the resources we had */
444 ncp->nc_vp = NULL;
445 ncp->nc_dvp = NULL;
446 TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
447 if (ncp->nc_hash.le_prev != NULL) {
448 LIST_REMOVE(ncp, nc_hash);
449 ncp->nc_hash.le_prev = NULL;
450 }
451 if (ncp->nc_vhash.le_prev != NULL) {
452 LIST_REMOVE(ncp, nc_vhash);
453 ncp->nc_vhash.le_prev = NULL;
454 }
455 pool_put(&nch_pool, ncp);
456 numcache--;
457 }
458 }