vfs_cache.c revision 6952
1/* 2 * Copyright (c) 1989, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)vfs_cache.c 8.3 (Berkeley) 8/22/94 34 * $Id: vfs_cache.c,v 1.6 1995/03/08 01:08:03 phk Exp $ 35 */ 36 37#include <sys/param.h> 38#include <sys/systm.h> 39#include <sys/time.h> 40#include <sys/mount.h> 41#include <sys/vnode.h> 42#include <sys/namei.h> 43#include <sys/errno.h> 44#include <sys/malloc.h> 45 46/* 47 * Name caching works as follows: 48 * 49 * Names found by directory scans are retained in a cache 50 * for future reference. It is managed LRU, so frequently 51 * used names will hang around. Cache is indexed by hash value 52 * obtained from (vp, name) where vp refers to the directory 53 * containing name. 54 * 55 * For simplicity (and economy of storage), names longer than 56 * a maximum length of NCHNAMLEN are not cached; they occur 57 * infrequently in any case, and are almost never of interest. 58 * 59 * Upon reaching the last segment of a path, if the reference 60 * is for DELETE, or NOCACHE is set (rewrite), and the 61 * name is located in the cache, it will be dropped. 62 */ 63 64/* 65 * Structures associated with name cacheing. 66 */ 67LIST_HEAD(nchashhead, namecache) *nchashtbl; /* Hash Table */ 68u_long nchash; /* size of hash table - 1 */ 69long numcache; /* number of cache entries allocated */ 70TAILQ_HEAD(, namecache) nclruhead; /* LRU chain */ 71struct nchstats nchstats; /* cache effectiveness statistics */ 72 73int doingcache = 1; /* 1 => enable the cache */ 74 75/* 76 * Look for a the name in the cache. We don't do this 77 * if the segment name is long, simply so the cache can avoid 78 * holding long names (which would either waste space, or 79 * add greatly to the complexity). 80 * 81 * Lookup is called with ni_dvp pointing to the directory to search, 82 * ni_ptr pointing to the name of the entry being sought, ni_namelen 83 * tells the length of the name, and ni_hash contains a hash of 84 * the name. If the lookup succeeds, the vnode is returned in ni_vp 85 * and a status of -1 is returned. If the lookup determines that 86 * the name does not exist (negative cacheing), a status of ENOENT 87 * is returned. If the lookup fails, a status of zero is returned. 88 */ 89int 90cache_lookup(dvp, vpp, cnp) 91 struct vnode *dvp; 92 struct vnode **vpp; 93 struct componentname *cnp; 94{ 95 register struct namecache *ncp,*nnp; 96 register struct nchashhead *ncpp; 97 98 if (!doingcache) { 99 cnp->cn_flags &= ~MAKEENTRY; 100 return (0); 101 } 102 if (cnp->cn_namelen > NCHNAMLEN) { 103 nchstats.ncs_long++; 104 cnp->cn_flags &= ~MAKEENTRY; 105 return (0); 106 } 107 ncpp = &nchashtbl[(dvp->v_id + cnp->cn_hash) & nchash]; 108 for (ncp = ncpp->lh_first; ncp != 0; ncp = nnp) { 109 if (ncp->nc_dvp == dvp && 110 ncp->nc_dvpid == dvp->v_id && 111 ncp->nc_nlen == cnp->cn_namelen && 112 !bcmp(ncp->nc_name, cnp->cn_nameptr, (u_int)ncp->nc_nlen)) 113 break; 114 nnp = ncp->nc_hash.le_next; 115 /* If one of the vp's went stale, don't bother anymore. */ 116 if ((ncp->nc_dvpid != ncp->nc_dvp->v_id) || 117 (ncp->nc_vp && (ncp->nc_vpid != ncp->nc_vp->v_id))) { 118 LIST_REMOVE(ncp, nc_hash); 119 ncp->nc_hash.le_prev = 0; 120 TAILQ_REMOVE(&nclruhead, ncp, nc_lru); 121 TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru); 122 } 123 } 124 if (ncp == 0) { 125 nchstats.ncs_miss++; 126 return (0); 127 } 128 if ((cnp->cn_flags & MAKEENTRY) == 0) { 129 nchstats.ncs_badhits++; 130 } else if (ncp->nc_vp == NULL) { 131 if (cnp->cn_nameiop != CREATE) { 132 nchstats.ncs_neghits++; 133 /* 134 * Move this slot to end of LRU chain, 135 * if not already there. 136 */ 137 if (ncp->nc_lru.tqe_next != 0) { 138 TAILQ_REMOVE(&nclruhead, ncp, nc_lru); 139 TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru); 140 } 141 return (ENOENT); 142 } 143 } else if (ncp->nc_vpid != ncp->nc_vp->v_id) { 144 nchstats.ncs_falsehits++; 145 } else { 146 nchstats.ncs_goodhits++; 147 /* 148 * move this slot to end of LRU chain, if not already there 149 */ 150 if (ncp->nc_lru.tqe_next != 0) { 151 TAILQ_REMOVE(&nclruhead, ncp, nc_lru); 152 TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru); 153 } 154 *vpp = ncp->nc_vp; 155 return (-1); 156 } 157 158 /* 159 * Last component and we are renaming or deleting, 160 * the cache entry is invalid, or otherwise don't 161 * want cache entry to exist. 162 */ 163 TAILQ_REMOVE(&nclruhead, ncp, nc_lru); 164 LIST_REMOVE(ncp, nc_hash); 165 ncp->nc_hash.le_prev = 0; 166 TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru); 167 return (0); 168} 169 170/* 171 * Add an entry to the cache 172 */ 173void 174cache_enter(dvp, vp, cnp) 175 struct vnode *dvp; 176 struct vnode *vp; 177 struct componentname *cnp; 178{ 179 register struct namecache *ncp; 180 register struct nchashhead *ncpp; 181 182#ifdef DIAGNOSTIC 183 if (cnp->cn_namelen > NCHNAMLEN) 184 panic("cache_enter: name too long"); 185#endif 186 if (!doingcache) 187 return; 188 /* 189 * Free the cache slot at head of lru chain. 190 */ 191 if (numcache < desiredvnodes) { 192 ncp = (struct namecache *) 193 malloc((u_long)sizeof *ncp, M_CACHE, M_WAITOK); 194 bzero((char *)ncp, sizeof *ncp); 195 numcache++; 196 } else if (ncp = nclruhead.tqh_first) { 197 TAILQ_REMOVE(&nclruhead, ncp, nc_lru); 198 if (ncp->nc_hash.le_prev != 0) { 199 LIST_REMOVE(ncp, nc_hash); 200 ncp->nc_hash.le_prev = 0; 201 } 202 } else 203 return; 204 /* grab the vnode we just found */ 205 ncp->nc_vp = vp; 206 if (vp) 207 ncp->nc_vpid = vp->v_id; 208 else 209 ncp->nc_vpid = 0; 210 /* fill in cache info */ 211 ncp->nc_dvp = dvp; 212 ncp->nc_dvpid = dvp->v_id; 213 ncp->nc_nlen = cnp->cn_namelen; 214 bcopy(cnp->cn_nameptr, ncp->nc_name, (unsigned)ncp->nc_nlen); 215 TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru); 216 ncpp = &nchashtbl[(dvp->v_id + cnp->cn_hash) & nchash]; 217 LIST_INSERT_HEAD(ncpp, ncp, nc_hash); 218} 219 220/* 221 * Name cache initialization, from vfs_init() when we are booting 222 */ 223void 224nchinit() 225{ 226 227 TAILQ_INIT(&nclruhead); 228 nchashtbl = hashinit(desiredvnodes, M_CACHE, &nchash); 229} 230 231/* 232 * Cache flush, a particular vnode; called when a vnode is renamed to 233 * hide entries that would now be invalid 234 */ 235void 236cache_purge(vp) 237 struct vnode *vp; 238{ 239 struct namecache *ncp; 240 struct nchashhead *ncpp; 241 242 vp->v_id = ++nextvnodeid; 243 if (nextvnodeid != 0) 244 return; 245 for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) { 246 for (ncp = ncpp->lh_first; ncp != 0; ncp = ncp->nc_hash.le_next) { 247 ncp->nc_vpid = 0; 248 ncp->nc_dvpid = 0; 249 } 250 } 251 vp->v_id = ++nextvnodeid; 252} 253 254/* 255 * Cache flush, a whole filesystem; called when filesys is umounted to 256 * remove entries that would now be invalid 257 * 258 * The line "nxtcp = nchhead" near the end is to avoid potential problems 259 * if the cache lru chain is modified while we are dumping the 260 * inode. This makes the algorithm O(n^2), but do you think I care? 261 */ 262void 263cache_purgevfs(mp) 264 struct mount *mp; 265{ 266 register struct namecache *ncp, *nxtcp; 267 268 for (ncp = nclruhead.tqh_first; ncp != 0; ncp = nxtcp) { 269 if (ncp->nc_dvp == NULL || ncp->nc_dvp->v_mount != mp) { 270 nxtcp = ncp->nc_lru.tqe_next; 271 continue; 272 } 273 /* free the resources we had */ 274 ncp->nc_vp = NULL; 275 ncp->nc_dvp = NULL; 276 TAILQ_REMOVE(&nclruhead, ncp, nc_lru); 277 if (ncp->nc_hash.le_prev != 0) { 278 LIST_REMOVE(ncp, nc_hash); 279 ncp->nc_hash.le_prev = 0; 280 } 281 /* cause rescan of list, it may have altered */ 282 nxtcp = nclruhead.tqh_first; 283 TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru); 284 } 285} 286