1 /* 2 * Copyright (c) 1989 The Regents of the University of California. 3 * All rights reserved. 4 * 5 * %sccs.include.redist.c% 6 * 7 * @(#)vfs_cache.c 7.7 (Berkeley) 08/24/90 8 */ 9 10 #include "param.h" 11 #include "systm.h" 12 #include "time.h" 13 #include "mount.h" 14 #include "vnode.h" 15 #include "namei.h" 16 #include "errno.h" 17 #include "malloc.h" 18 19 /* 20 * Name caching works as follows: 21 * 22 * Names found by directory scans are retained in a cache 23 * for future reference. It is managed LRU, so frequently 24 * used names will hang around. Cache is indexed by hash value 25 * obtained from (vp, name) where vp refers to the directory 26 * containing name. 27 * 28 * For simplicity (and economy of storage), names longer than 29 * a maximum length of NCHNAMLEN are not cached; they occur 30 * infrequently in any case, and are almost never of interest. 31 * 32 * Upon reaching the last segment of a path, if the reference 33 * is for DELETE, or NOCACHE is set (rewrite), and the 34 * name is located in the cache, it will be dropped. 35 */ 36 37 /* 38 * Structures associated with name cacheing. 39 */ 40 union nchash { 41 union nchash *nch_head[2]; 42 struct namecache *nch_chain[2]; 43 } *nchashtbl; 44 #define nch_forw nch_chain[0] 45 #define nch_back nch_chain[1] 46 47 u_long nchash; /* size of hash table - 1 */ 48 long numcache; /* number of cache entries allocated */ 49 struct namecache *nchhead, **nchtail; /* LRU chain pointers */ 50 struct nchstats nchstats; /* cache effectiveness statistics */ 51 52 int doingcache = 1; /* 1 => enable the cache */ 53 54 /* 55 * Look for a the name in the cache. We don't do this 56 * if the segment name is long, simply so the cache can avoid 57 * holding long names (which would either waste space, or 58 * add greatly to the complexity). 59 * 60 * Lookup is called with ni_dvp pointing to the directory to search, 61 * ni_ptr pointing to the name of the entry being sought, ni_namelen 62 * tells the length of the name, and ni_hash contains a hash of 63 * the name. If the lookup succeeds, the vnode is returned in ni_vp 64 * and a status of -1 is returned. If the lookup determines that 65 * the name does not exist (negative cacheing), a status of ENOENT 66 * is returned. If the lookup fails, a status of zero is returned. 67 */ 68 cache_lookup(ndp) 69 register struct nameidata *ndp; 70 { 71 register struct vnode *dvp; 72 register struct namecache *ncp; 73 union nchash *nhp; 74 75 if (!doingcache) 76 return (0); 77 if (ndp->ni_namelen > NCHNAMLEN) { 78 nchstats.ncs_long++; 79 ndp->ni_makeentry = 0; 80 return (0); 81 } 82 dvp = ndp->ni_dvp; 83 nhp = &nchashtbl[ndp->ni_hash & nchash]; 84 for (ncp = nhp->nch_forw; ncp != (struct namecache *)nhp; 85 ncp = ncp->nc_forw) { 86 if (ncp->nc_dvp == dvp && 87 ncp->nc_dvpid == dvp->v_id && 88 ncp->nc_nlen == ndp->ni_namelen && 89 !bcmp(ncp->nc_name, ndp->ni_ptr, (unsigned)ncp->nc_nlen)) 90 break; 91 } 92 if (ncp == (struct namecache *)nhp) { 93 nchstats.ncs_miss++; 94 return (0); 95 } 96 if (!ndp->ni_makeentry) { 97 nchstats.ncs_badhits++; 98 } else if (ncp->nc_vp == NULL) { 99 nchstats.ncs_neghits++; 100 /* 101 * move this slot to end of LRU chain, if not already there 102 */ 103 if (ncp->nc_nxt) { 104 /* remove from LRU chain */ 105 *ncp->nc_prev = ncp->nc_nxt; 106 ncp->nc_nxt->nc_prev = ncp->nc_prev; 107 /* and replace at end of it */ 108 ncp->nc_nxt = NULL; 109 ncp->nc_prev = nchtail; 110 *nchtail = ncp; 111 nchtail = &ncp->nc_nxt; 112 } 113 return (ENOENT); 114 } else if (ncp->nc_vpid != ncp->nc_vp->v_id) { 115 nchstats.ncs_falsehits++; 116 } else { 117 nchstats.ncs_goodhits++; 118 /* 119 * move this slot to end of LRU chain, if not already there 120 */ 121 if (ncp->nc_nxt) { 122 /* remove from LRU chain */ 123 *ncp->nc_prev = ncp->nc_nxt; 124 ncp->nc_nxt->nc_prev = ncp->nc_prev; 125 /* and replace at end of it */ 126 ncp->nc_nxt = NULL; 127 ncp->nc_prev = nchtail; 128 *nchtail = ncp; 129 nchtail = &ncp->nc_nxt; 130 } 131 ndp->ni_vp = ncp->nc_vp; 132 return (-1); 133 } 134 135 /* 136 * Last component and we are renaming or deleting, 137 * the cache entry is invalid, or otherwise don't 138 * want cache entry to exist. 139 */ 140 /* remove from LRU chain */ 141 *ncp->nc_prev = ncp->nc_nxt; 142 if (ncp->nc_nxt) 143 ncp->nc_nxt->nc_prev = ncp->nc_prev; 144 else 145 nchtail = ncp->nc_prev; 146 /* remove from hash chain */ 147 remque(ncp); 148 /* insert at head of LRU list (first to grab) */ 149 ncp->nc_nxt = nchhead; 150 ncp->nc_prev = &nchhead; 151 nchhead->nc_prev = &ncp->nc_nxt; 152 nchhead = ncp; 153 /* and make a dummy hash chain */ 154 ncp->nc_forw = ncp; 155 ncp->nc_back = ncp; 156 return (0); 157 } 158 159 /* 160 * Add an entry to the cache 161 */ 162 cache_enter(ndp) 163 register struct nameidata *ndp; 164 { 165 register struct namecache *ncp; 166 union nchash *nhp; 167 168 if (!doingcache) 169 return; 170 /* 171 * Free the cache slot at head of lru chain. 172 */ 173 if (numcache < desiredvnodes) { 174 ncp = (struct namecache *) 175 malloc((u_long)sizeof *ncp, M_CACHE, M_WAITOK); 176 bzero((char *)ncp, sizeof *ncp); 177 numcache++; 178 } else if (ncp = nchhead) { 179 /* remove from lru chain */ 180 *ncp->nc_prev = ncp->nc_nxt; 181 if (ncp->nc_nxt) 182 ncp->nc_nxt->nc_prev = ncp->nc_prev; 183 else 184 nchtail = ncp->nc_prev; 185 /* remove from old hash chain */ 186 remque(ncp); 187 } else 188 return; 189 /* grab the vnode we just found */ 190 ncp->nc_vp = ndp->ni_vp; 191 if (ndp->ni_vp) 192 ncp->nc_vpid = ndp->ni_vp->v_id; 193 else 194 ncp->nc_vpid = 0; 195 /* fill in cache info */ 196 ncp->nc_dvp = ndp->ni_dvp; 197 ncp->nc_dvpid = ndp->ni_dvp->v_id; 198 ncp->nc_nlen = ndp->ni_namelen; 199 bcopy(ndp->ni_ptr, ncp->nc_name, (unsigned)ncp->nc_nlen); 200 /* link at end of lru chain */ 201 ncp->nc_nxt = NULL; 202 ncp->nc_prev = nchtail; 203 *nchtail = ncp; 204 nchtail = &ncp->nc_nxt; 205 /* and insert on hash chain */ 206 nhp = &nchashtbl[ndp->ni_hash & nchash]; 207 insque(ncp, nhp); 208 } 209 210 /* 211 * Name cache initialization, from vfs_init() when we are booting 212 */ 213 nchinit() 214 { 215 register union nchash *nchp; 216 long nchashsize; 217 218 nchhead = 0; 219 nchtail = &nchhead; 220 nchashsize = roundup((desiredvnodes + 1) * sizeof *nchp / 2, 221 NBPG * CLSIZE); 222 nchashtbl = (union nchash *)malloc((u_long)nchashsize, 223 M_CACHE, M_WAITOK); 224 for (nchash = 1; nchash <= nchashsize / sizeof *nchp; nchash <<= 1) 225 /* void */; 226 nchash = (nchash >> 1) - 1; 227 for (nchp = &nchashtbl[nchash]; nchp >= nchashtbl; nchp--) { 228 nchp->nch_head[0] = nchp; 229 nchp->nch_head[1] = nchp; 230 } 231 } 232 233 /* 234 * Cache flush, a particular vnode; called when a vnode is renamed to 235 * hide entries that would now be invalid 236 */ 237 cache_purge(vp) 238 struct vnode *vp; 239 { 240 union nchash *nhp; 241 struct namecache *ncp; 242 243 vp->v_id = ++nextvnodeid; 244 if (nextvnodeid != 0) 245 return; 246 for (nhp = &nchashtbl[nchash]; nhp >= nchashtbl; nhp--) { 247 for (ncp = nhp->nch_forw; ncp != (struct namecache *)nhp; 248 ncp = ncp->nc_forw) { 249 ncp->nc_vpid = 0; 250 ncp->nc_dvpid = 0; 251 } 252 } 253 vp->v_id = ++nextvnodeid; 254 } 255 256 /* 257 * Cache flush, a whole filesystem; called when filesys is umounted to 258 * remove entries that would now be invalid 259 * 260 * The line "nxtcp = nchhead" near the end is to avoid potential problems 261 * if the cache lru chain is modified while we are dumping the 262 * inode. This makes the algorithm O(n^2), but do you think I care? 263 */ 264 cache_purgevfs(mp) 265 struct mount *mp; 266 { 267 register struct namecache *ncp, *nxtcp; 268 269 for (ncp = nchhead; ncp; ncp = nxtcp) { 270 nxtcp = ncp->nc_nxt; 271 if (ncp->nc_dvp == NULL || ncp->nc_dvp->v_mount != mp) 272 continue; 273 /* free the resources we had */ 274 ncp->nc_vp = NULL; 275 ncp->nc_dvp = NULL; 276 remque(ncp); /* remove entry from its hash chain */ 277 ncp->nc_forw = ncp; /* and make a dummy one */ 278 ncp->nc_back = ncp; 279 /* delete this entry from LRU chain */ 280 *ncp->nc_prev = nxtcp; 281 if (nxtcp) 282 nxtcp->nc_prev = ncp->nc_prev; 283 else 284 nchtail = ncp->nc_prev; 285 /* cause rescan of list, it may have altered */ 286 nxtcp = nchhead; 287 /* put the now-free entry at head of LRU */ 288 ncp->nc_nxt = nxtcp; 289 ncp->nc_prev = &nchhead; 290 nxtcp->nc_prev = &ncp->nc_nxt; 291 nchhead = ncp; 292 } 293 } 294