Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/kern/vfs_cache.c
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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 * 3. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)vfs_cache.c 8.5 (Berkeley) 3/22/95 37 * $FreeBSD$ 38 */ 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/kernel.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 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 * If it is a "negative" entry, (i.e. for a name that is known NOT to 60 * exist) the vnode pointer will be NULL. 61 * 62 * Upon reaching the last segment of a path, if the reference 63 * is for DELETE, or NOCACHE is set (rewrite), and the 64 * name is located in the cache, it will be dropped. 65 */ 66 67 /* 68 * Structures associated with name cacheing. 69 */ 70 #define NCHHASH(dvp, cnp) \ 71 (&nchashtbl[((dvp)->v_id + (cnp)->cn_hash) & nchash]) 72 static LIST_HEAD(nchashhead, namecache) *nchashtbl; /* Hash Table */ 73 static TAILQ_HEAD(, namecache) ncneg; /* Hash Table */ 74 static u_long nchash; /* size of hash table */ 75 SYSCTL_INT(_debug, OID_AUTO, nchash, CTLFLAG_RD, &nchash, 0, ""); 76 static u_long ncnegfactor = 16; /* ratio of negative entries */ 77 SYSCTL_INT(_debug, OID_AUTO, ncnegfactor, CTLFLAG_RW, &ncnegfactor, 0, ""); 78 static u_long numneg; /* number of cache entries allocated */ 79 SYSCTL_INT(_debug, OID_AUTO, numneg, CTLFLAG_RD, &numneg, 0, ""); 80 static u_long numcache; /* number of cache entries allocated */ 81 SYSCTL_INT(_debug, OID_AUTO, numcache, CTLFLAG_RD, &numcache, 0, ""); 82 struct nchstats nchstats; /* cache effectiveness statistics */ 83 84 static int doingcache = 1; /* 1 => enable the cache */ 85 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, ""); 86 SYSCTL_INT(_debug, OID_AUTO, vnsize, CTLFLAG_RD, 0, sizeof(struct vnode), ""); 87 SYSCTL_INT(_debug, OID_AUTO, ncsize, CTLFLAG_RD, 0, sizeof(struct namecache), ""); 88 89 /* 90 * The new name cache statistics 91 */ 92 SYSCTL_NODE(_vfs, OID_AUTO, cache, CTLFLAG_RW, 0, "Name cache statistics"); 93 #define STATNODE(mode, name, var) \ 94 SYSCTL_INT(_vfs_cache, OID_AUTO, name, mode, var, 0, ""); 95 STATNODE(CTLFLAG_RD, numneg, &numneg); 96 STATNODE(CTLFLAG_RD, numcache, &numcache); 97 static u_long numcalls; STATNODE(CTLFLAG_RD, numcalls, &numcalls); 98 static u_long dothits; STATNODE(CTLFLAG_RD, dothits, &dothits); 99 static u_long dotdothits; STATNODE(CTLFLAG_RD, dotdothits, &dotdothits); 100 static u_long numchecks; STATNODE(CTLFLAG_RD, numchecks, &numchecks); 101 static u_long nummiss; STATNODE(CTLFLAG_RD, nummiss, &nummiss); 102 static u_long nummisszap; STATNODE(CTLFLAG_RD, nummisszap, &nummisszap); 103 static u_long numposzaps; STATNODE(CTLFLAG_RD, numposzaps, &numposzaps); 104 static u_long numposhits; STATNODE(CTLFLAG_RD, numposhits, &numposhits); 105 static u_long numnegzaps; STATNODE(CTLFLAG_RD, numnegzaps, &numnegzaps); 106 static u_long numneghits; STATNODE(CTLFLAG_RD, numneghits, &numneghits); 107 108 /* 109 * Max aliases to a name, avoids DoS of the system via hardlinks 110 */ 111 static int ncmaxaliases = 4; 112 SYSCTL_INT(_vfs_cache, OID_AUTO, maxaliases, CTLFLAG_RW, &ncmaxaliases, 4, 113 "Maximum amount of cache entries that can point to a particular file"); 114 115 static void cache_zap __P((struct namecache *ncp)); 116 117 /* 118 * Flags in namecache.nc_flag 119 */ 120 #define NCF_WHITE 1 121 /* 122 * Delete an entry from its hash list and move it to the front 123 * of the LRU list for immediate reuse. 124 */ 125 static void 126 cache_zap(ncp) 127 struct namecache *ncp; 128 { 129 LIST_REMOVE(ncp, nc_hash); 130 LIST_REMOVE(ncp, nc_src); 131 if (LIST_EMPTY(&ncp->nc_dvp->v_cache_src)) 132 vdrop(ncp->nc_dvp); 133 if (ncp->nc_vp) { 134 TAILQ_REMOVE(&ncp->nc_vp->v_cache_dst, ncp, nc_dst); 135 ncp->nc_vp->v_cache_dst_count--; 136 } else { 137 TAILQ_REMOVE(&ncneg, ncp, nc_dst); 138 numneg--; 139 } 140 numcache--; 141 free(ncp, M_CACHE); 142 } 143 144 /* 145 * Lookup an entry in the cache 146 * 147 * We don't do this if the segment name is long, simply so the cache 148 * can avoid holding long names (which would either waste space, or 149 * add greatly to the complexity). 150 * 151 * Lookup is called with dvp pointing to the directory to search, 152 * cnp pointing to the name of the entry being sought. If the lookup 153 * succeeds, the vnode is returned in *vpp, and a status of -1 is 154 * returned. If the lookup determines that the name does not exist 155 * (negative cacheing), a status of ENOENT is returned. If the lookup 156 * fails, a status of zero is returned. 157 */ 158 159 int 160 cache_lookup(dvp, vpp, cnp) 161 struct vnode *dvp; 162 struct vnode **vpp; 163 struct componentname *cnp; 164 { 165 register struct namecache *ncp; 166 167 if (!doingcache) { 168 cnp->cn_flags &= ~MAKEENTRY; 169 return (0); 170 } 171 172 numcalls++; 173 174 if (cnp->cn_nameptr[0] == '.') { 175 if (cnp->cn_namelen == 1) { 176 *vpp = dvp; 177 dothits++; 178 return (-1); 179 } 180 if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') { 181 dotdothits++; 182 if (dvp->v_dd->v_id != dvp->v_ddid || 183 (cnp->cn_flags & MAKEENTRY) == 0) { 184 dvp->v_ddid = 0; 185 return (0); 186 } 187 *vpp = dvp->v_dd; 188 return (-1); 189 } 190 } 191 192 LIST_FOREACH(ncp, (NCHHASH(dvp, cnp)), nc_hash) { 193 numchecks++; 194 if (ncp->nc_dvp == dvp && ncp->nc_nlen == cnp->cn_namelen && 195 !bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen)) 196 break; 197 } 198 199 /* We failed to find an entry */ 200 if (ncp == 0) { 201 if ((cnp->cn_flags & MAKEENTRY) == 0) { 202 nummisszap++; 203 } else { 204 nummiss++; 205 } 206 nchstats.ncs_miss++; 207 return (0); 208 } 209 210 /* We don't want to have an entry, so dump it */ 211 if ((cnp->cn_flags & MAKEENTRY) == 0) { 212 numposzaps++; 213 nchstats.ncs_badhits++; 214 cache_zap(ncp); 215 return (0); 216 } 217 218 /* We found a "positive" match, return the vnode */ 219 if (ncp->nc_vp) { 220 numposhits++; 221 nchstats.ncs_goodhits++; 222 *vpp = ncp->nc_vp; 223 return (-1); 224 } 225 226 /* We found a negative match, and want to create it, so purge */ 227 if (cnp->cn_nameiop == CREATE) { 228 numnegzaps++; 229 nchstats.ncs_badhits++; 230 cache_zap(ncp); 231 return (0); 232 } 233 234 numneghits++; 235 /* 236 * We found a "negative" match, ENOENT notifies client of this match. 237 * The nc_vpid field records whether this is a whiteout. 238 */ 239 TAILQ_REMOVE(&ncneg, ncp, nc_dst); 240 TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst); 241 nchstats.ncs_neghits++; 242 if (ncp->nc_flag & NCF_WHITE) 243 cnp->cn_flags |= ISWHITEOUT; 244 return (ENOENT); 245 } 246 247 /* 248 * Add an entry to the cache. 249 */ 250 void 251 cache_enter(dvp, vp, cnp) 252 struct vnode *dvp; 253 struct vnode *vp; 254 struct componentname *cnp; 255 { 256 register struct namecache *ncp; 257 register struct nchashhead *ncpp; 258 259 if (!doingcache) 260 return; 261 262 if (cnp->cn_nameptr[0] == '.') { 263 if (cnp->cn_namelen == 1) { 264 return; 265 } 266 if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') { 267 if (vp) { 268 dvp->v_dd = vp; 269 dvp->v_ddid = vp->v_id; 270 } else { 271 dvp->v_dd = dvp; 272 dvp->v_ddid = 0; 273 } 274 return; 275 } 276 } 277 278 ncp = (struct namecache *) 279 malloc(sizeof *ncp + cnp->cn_namelen, M_CACHE, M_WAITOK); 280 bzero((char *)ncp, sizeof *ncp); 281 numcache++; 282 if (!vp) { 283 numneg++; 284 ncp->nc_flag = cnp->cn_flags & ISWHITEOUT ? NCF_WHITE : 0; 285 } else if (vp->v_type == VDIR) { 286 vp->v_dd = dvp; 287 vp->v_ddid = dvp->v_id; 288 } 289 290 /* 291 * Fill in cache info, if vp is NULL this is a "negative" cache entry. 292 * For negative entries, we have to record whether it is a whiteout. 293 * the whiteout flag is stored in the nc_vpid field which is 294 * otherwise unused. 295 */ 296 ncp->nc_vp = vp; 297 ncp->nc_dvp = dvp; 298 ncp->nc_nlen = cnp->cn_namelen; 299 bcopy(cnp->cn_nameptr, ncp->nc_name, ncp->nc_nlen); 300 ncpp = NCHHASH(dvp, cnp); 301 LIST_INSERT_HEAD(ncpp, ncp, nc_hash); 302 if (LIST_EMPTY(&dvp->v_cache_src)) 303 vhold(dvp); 304 LIST_INSERT_HEAD(&dvp->v_cache_src, ncp, nc_src); 305 if (vp) { 306 while (vp->v_cache_dst_count > ncmaxaliases) 307 cache_zap(TAILQ_LAST(&vp->v_cache_dst, cdst)); 308 vp->v_cache_dst_count++; 309 TAILQ_INSERT_HEAD(&vp->v_cache_dst, ncp, nc_dst); 310 } else { 311 TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst); 312 } 313 if (numneg*ncnegfactor > numcache) { 314 ncp = TAILQ_FIRST(&ncneg); 315 cache_zap(ncp); 316 } 317 } 318 319 /* 320 * Name cache initialization, from vfs_init() when we are booting 321 */ 322 void 323 nchinit() 324 { 325 326 TAILQ_INIT(&ncneg); 327 nchashtbl = hashinit(desiredvnodes*2, M_CACHE, &nchash); 328 } 329 330 /* 331 * Invalidate all entries to a particular vnode. 332 * 333 * Remove all entries in the namecache relating to this vnode and 334 * change the v_id. We take the v_id from a global counter, since 335 * it becomes a handy sequence number in crash-dumps that way. 336 * No valid vnode will ever have (v_id == 0). 337 * 338 * XXX: Only time and the size of v_id prevents this from failing: 339 * XXX: In theory we should hunt down all (struct vnode*, v_id) 340 * XXX: soft references and nuke them, at least on the global 341 * XXX: v_id wraparound. The period of resistance can be extended 342 * XXX: by incrementing each vnodes v_id individually instead of 343 * XXX: using the global v_id. 344 */ 345 346 void 347 cache_purge(vp) 348 struct vnode *vp; 349 { 350 static u_long nextid; 351 352 while (!LIST_EMPTY(&vp->v_cache_src)) 353 cache_zap(LIST_FIRST(&vp->v_cache_src)); 354 while (!TAILQ_EMPTY(&vp->v_cache_dst)) 355 cache_zap(TAILQ_FIRST(&vp->v_cache_dst)); 356 357 do 358 nextid++; 359 while (nextid == vp->v_id || !nextid); 360 vp->v_id = nextid; 361 vp->v_dd = vp; 362 vp->v_ddid = 0; 363 } 364 365 /* 366 * Flush all entries referencing a particular filesystem. 367 * 368 * Since we need to check it anyway, we will flush all the invalid 369 * entries at the same time. 370 */ 371 void 372 cache_purgevfs(mp) 373 struct mount *mp; 374 { 375 struct nchashhead *ncpp; 376 struct namecache *ncp, *nnp; 377 378 /* Scan hash tables for applicable entries */ 379 for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) { 380 for (ncp = LIST_FIRST(ncpp); ncp != 0; ncp = nnp) { 381 nnp = LIST_NEXT(ncp, nc_hash); 382 if (ncp->nc_dvp->v_mount == mp) { 383 cache_zap(ncp); 384 } 385 } 386 } 387 } 388 389 /* 390 * Perform canonical checks and cache lookup and pass on to filesystem 391 * through the vop_cachedlookup only if needed. 392 */ 393 394 int 395 vfs_cache_lookup(ap) 396 struct vop_lookup_args /* { 397 struct vnode *a_dvp; 398 struct vnode **a_vpp; 399 struct componentname *a_cnp; 400 } */ *ap; 401 { 402 struct vnode *vdp; 403 struct vnode *pdp; 404 int lockparent; 405 int error; 406 struct vnode **vpp = ap->a_vpp; 407 struct componentname *cnp = ap->a_cnp; 408 struct ucred *cred = cnp->cn_cred; 409 int flags = cnp->cn_flags; 410 struct proc *p = cnp->cn_proc; 411 u_long vpid; /* capability number of vnode */ 412 413 *vpp = NULL; 414 vdp = ap->a_dvp; 415 lockparent = flags & LOCKPARENT; 416 417 if (vdp->v_type != VDIR) 418 return (ENOTDIR); 419 420 if ((flags & ISLASTCN) && (vdp->v_mount->mnt_flag & MNT_RDONLY) && 421 (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) 422 return (EROFS); 423 424 error = VOP_ACCESS(vdp, VEXEC, cred, cnp->cn_proc); 425 426 if (error) 427 return (error); 428 429 error = cache_lookup(vdp, vpp, cnp); 430 431 if (!error) 432 return (VOP_CACHEDLOOKUP(ap->a_dvp, ap->a_vpp, ap->a_cnp)); 433 434 if (error == ENOENT) 435 return (error); 436 437 pdp = vdp; 438 vdp = *vpp; 439 vpid = vdp->v_id; 440 if (pdp == vdp) { /* lookup on "." */ 441 VREF(vdp); 442 error = 0; 443 } else if (flags & ISDOTDOT) { 444 VOP_UNLOCK(pdp, 0, p); 445 error = vget(vdp, LK_EXCLUSIVE, p); 446 if (!error && lockparent && (flags & ISLASTCN)) 447 error = vn_lock(pdp, LK_EXCLUSIVE, p); 448 } else { 449 error = vget(vdp, LK_EXCLUSIVE, p); 450 if (!lockparent || error || !(flags & ISLASTCN)) 451 VOP_UNLOCK(pdp, 0, p); 452 } 453 /* 454 * Check that the capability number did not change 455 * while we were waiting for the lock. 456 */ 457 if (!error) { 458 if (vpid == vdp->v_id) 459 return (0); 460 vput(vdp); 461 if (lockparent && pdp != vdp && (flags & ISLASTCN)) 462 VOP_UNLOCK(pdp, 0, p); 463 } 464 error = vn_lock(pdp, LK_EXCLUSIVE, p); 465 if (error) 466 return (error); 467 return (VOP_CACHEDLOOKUP(ap->a_dvp, ap->a_vpp, ap->a_cnp)); 468 }
Cache object: ca81b45dee981fe4e1fa5e59cb6dbd5b
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