1 /* $OpenBSD: vfs_cache.c,v 1.26 2008/05/06 20:57:19 thib 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|PR_ZERO); 349 numcache++; 350 } else if ((ncp = TAILQ_FIRST(&nclruhead)) != NULL) { 351 TAILQ_REMOVE(&nclruhead, ncp, nc_lru); 352 if (ncp->nc_hash.le_prev != NULL) { 353 LIST_REMOVE(ncp, nc_hash); 354 ncp->nc_hash.le_prev = NULL; 355 } 356 if (ncp->nc_vhash.le_prev != NULL) { 357 LIST_REMOVE(ncp, nc_vhash); 358 ncp->nc_vhash.le_prev = NULL; 359 } 360 } else 361 return; 362 /* grab the vnode we just found */ 363 ncp->nc_vp = vp; 364 if (vp) 365 ncp->nc_vpid = vp->v_id; 366 /* fill in cache info */ 367 ncp->nc_dvp = dvp; 368 ncp->nc_dvpid = dvp->v_id; 369 ncp->nc_nlen = cnp->cn_namelen; 370 bcopy(cnp->cn_nameptr, ncp->nc_name, (unsigned)ncp->nc_nlen); 371 TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru); 372 ncpp = &nchashtbl[NCHASH(dvp, cnp)]; 373 LIST_INSERT_HEAD(ncpp, ncp, nc_hash); 374 375 /* 376 * Create reverse-cache entries (used in getcwd) for 377 * directories. 378 */ 379 380 ncp->nc_vhash.le_prev = NULL; 381 ncp->nc_vhash.le_next = NULL; 382 383 if (vp && vp != dvp && vp->v_type == VDIR && 384 (ncp->nc_nlen > 2 || 385 (ncp->nc_nlen > 1 && ncp->nc_name[1] != '.') || 386 (ncp->nc_nlen > 0 && ncp->nc_name[0] != '.'))) { 387 nvcpp = &ncvhashtbl[NCVHASH(vp)]; 388 LIST_INSERT_HEAD(nvcpp, ncp, nc_vhash); 389 } 390 } 391 392 /* 393 * Name cache initialization, from vfs_init() when we are booting 394 */ 395 void 396 nchinit(void) 397 { 398 399 TAILQ_INIT(&nclruhead); 400 nchashtbl = hashinit(desiredvnodes, M_CACHE, M_WAITOK, &nchash); 401 ncvhashtbl = hashinit(desiredvnodes/8, M_CACHE, M_WAITOK, &ncvhash); 402 pool_init(&nch_pool, sizeof(struct namecache), 0, 0, 0, "nchpl", 403 &pool_allocator_nointr); 404 } 405 406 /* 407 * Cache flush, a particular vnode; called when a vnode is renamed to 408 * hide entries that would now be invalid 409 */ 410 void 411 cache_purge(struct vnode *vp) 412 { 413 struct namecache *ncp; 414 struct nchashhead *ncpp; 415 416 vp->v_id = ++nextvnodeid; 417 if (nextvnodeid != 0) 418 return; 419 for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) { 420 LIST_FOREACH(ncp, ncpp, nc_hash) { 421 ncp->nc_vpid = 0; 422 ncp->nc_dvpid = 0; 423 } 424 } 425 vp->v_id = ++nextvnodeid; 426 } 427 428 /* 429 * Cache flush, a whole filesystem; called when filesys is umounted to 430 * remove entries that would now be invalid 431 */ 432 void 433 cache_purgevfs(struct mount *mp) 434 { 435 struct namecache *ncp, *nxtcp; 436 437 for (ncp = TAILQ_FIRST(&nclruhead); ncp != TAILQ_END(&nclruhead); 438 ncp = nxtcp) { 439 nxtcp = TAILQ_NEXT(ncp, nc_lru); 440 if (ncp->nc_dvp == NULL || ncp->nc_dvp->v_mount != mp) 441 continue; 442 /* free the resources we had */ 443 ncp->nc_vp = NULL; 444 ncp->nc_dvp = NULL; 445 TAILQ_REMOVE(&nclruhead, ncp, nc_lru); 446 if (ncp->nc_hash.le_prev != NULL) { 447 LIST_REMOVE(ncp, nc_hash); 448 ncp->nc_hash.le_prev = NULL; 449 } 450 if (ncp->nc_vhash.le_prev != NULL) { 451 LIST_REMOVE(ncp, nc_vhash); 452 ncp->nc_vhash.le_prev = NULL; 453 } 454 pool_put(&nch_pool, ncp); 455 numcache--; 456 } 457 } 458