Annotation of sys/kern/vfs_cache.c, Revision 1.1.1.1
1.1 nbrk 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: }
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