| 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 7.15 (Berkeley) %G% |
| 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 | struct namecache **nchashtbl; |
| 41 | u_long nchash; /* size of hash table - 1 */ |
| 42 | long numcache; /* number of cache entries allocated */ |
| 43 | struct namecache *nchhead, **nchtail; /* LRU chain pointers */ |
| 44 | struct nchstats nchstats; /* cache effectiveness statistics */ |
| 45 | |
| 46 | int doingcache = 1; /* 1 => enable the cache */ |
| 47 | |
| 48 | /* |
| 49 | * Look for a the name in the cache. We don't do this |
| 50 | * if the segment name is long, simply so the cache can avoid |
| 51 | * holding long names (which would either waste space, or |
| 52 | * add greatly to the complexity). |
| 53 | * |
| 54 | * Lookup is called with ni_dvp pointing to the directory to search, |
| 55 | * ni_ptr pointing to the name of the entry being sought, ni_namelen |
| 56 | * tells the length of the name, and ni_hash contains a hash of |
| 57 | * the name. If the lookup succeeds, the vnode is returned in ni_vp |
| 58 | * and a status of -1 is returned. If the lookup determines that |
| 59 | * the name does not exist (negative cacheing), a status of ENOENT |
| 60 | * is returned. If the lookup fails, a status of zero is returned. |
| 61 | */ |
| 62 | int |
| 63 | cache_lookup(dvp, vpp, cnp) |
| 64 | struct vnode *dvp; |
| 65 | struct vnode **vpp; |
| 66 | struct componentname *cnp; |
| 67 | { |
| 68 | register struct namecache *ncp, *ncq, **ncpp; |
| 69 | |
| 70 | if (!doingcache) |
| 71 | return (0); |
| 72 | if (cnp->cn_namelen > NCHNAMLEN) { |
| 73 | nchstats.ncs_long++; |
| 74 | cnp->cn_flags &= ~MAKEENTRY; |
| 75 | return (0); |
| 76 | } |
| 77 | ncpp = &nchashtbl[cnp->cn_hash & nchash]; |
| 78 | for (ncp = *ncpp; ncp; ncp = ncp->nc_forw) { |
| 79 | if (ncp->nc_dvp == dvp && |
| 80 | ncp->nc_dvpid == dvp->v_id && |
| 81 | ncp->nc_nlen == cnp->cn_namelen && |
| 82 | !bcmp(ncp->nc_name, cnp->cn_nameptr, (u_int)ncp->nc_nlen)) |
| 83 | break; |
| 84 | } |
| 85 | if (ncp == NULL) { |
| 86 | nchstats.ncs_miss++; |
| 87 | return (0); |
| 88 | } |
| 89 | if (!(cnp->cn_flags & MAKEENTRY)) { |
| 90 | nchstats.ncs_badhits++; |
| 91 | } else if (ncp->nc_vp == NULL) { |
| 92 | if (cnp->cn_nameiop != CREATE) { |
| 93 | nchstats.ncs_neghits++; |
| 94 | /* |
| 95 | * Move this slot to end of LRU chain, |
| 96 | * if not already there. |
| 97 | */ |
| 98 | if (ncp->nc_nxt) { |
| 99 | /* remove from LRU chain */ |
| 100 | *ncp->nc_prev = ncp->nc_nxt; |
| 101 | ncp->nc_nxt->nc_prev = ncp->nc_prev; |
| 102 | /* and replace at end of it */ |
| 103 | ncp->nc_nxt = NULL; |
| 104 | ncp->nc_prev = nchtail; |
| 105 | *nchtail = ncp; |
| 106 | nchtail = &ncp->nc_nxt; |
| 107 | } |
| 108 | return (ENOENT); |
| 109 | } |
| 110 | } else if (ncp->nc_vpid != ncp->nc_vp->v_id) { |
| 111 | nchstats.ncs_falsehits++; |
| 112 | } else { |
| 113 | nchstats.ncs_goodhits++; |
| 114 | /* |
| 115 | * move this slot to end of LRU chain, if not already there |
| 116 | */ |
| 117 | if (ncp->nc_nxt) { |
| 118 | /* remove from LRU chain */ |
| 119 | *ncp->nc_prev = ncp->nc_nxt; |
| 120 | ncp->nc_nxt->nc_prev = ncp->nc_prev; |
| 121 | /* and replace at end of it */ |
| 122 | ncp->nc_nxt = NULL; |
| 123 | ncp->nc_prev = nchtail; |
| 124 | *nchtail = ncp; |
| 125 | nchtail = &ncp->nc_nxt; |
| 126 | } |
| 127 | *vpp = ncp->nc_vp; |
| 128 | return (-1); |
| 129 | } |
| 130 | |
| 131 | /* |
| 132 | * Last component and we are renaming or deleting, |
| 133 | * the cache entry is invalid, or otherwise don't |
| 134 | * want cache entry to exist. |
| 135 | */ |
| 136 | /* remove from LRU chain */ |
| 137 | if (ncq = ncp->nc_nxt) |
| 138 | ncq->nc_prev = ncp->nc_prev; |
| 139 | else |
| 140 | nchtail = ncp->nc_prev; |
| 141 | *ncp->nc_prev = ncq; |
| 142 | /* remove from hash chain */ |
| 143 | if (ncq = ncp->nc_forw) |
| 144 | ncq->nc_back = ncp->nc_back; |
| 145 | *ncp->nc_back = ncq; |
| 146 | /* and make a dummy hash chain */ |
| 147 | ncp->nc_forw = NULL; |
| 148 | ncp->nc_back = NULL; |
| 149 | /* insert at head of LRU list (first to grab) */ |
| 150 | if (ncq = nchhead) |
| 151 | ncq->nc_prev = &ncp->nc_nxt; |
| 152 | else |
| 153 | nchtail = &ncp->nc_nxt; |
| 154 | nchhead = ncp; |
| 155 | ncp->nc_nxt = ncq; |
| 156 | ncp->nc_prev = &nchhead; |
| 157 | return (0); |
| 158 | } |
| 159 | |
| 160 | /* |
| 161 | * Add an entry to the cache |
| 162 | */ |
| 163 | cache_enter(dvp, vp, cnp) |
| 164 | struct vnode *dvp; |
| 165 | struct vnode *vp; |
| 166 | struct componentname *cnp; |
| 167 | { |
| 168 | register struct namecache *ncp, *ncq, **ncpp; |
| 169 | |
| 170 | #ifdef DIAGNOSTIC |
| 171 | if (cnp->cn_namelen > NCHNAMLEN) |
| 172 | panic("cache_enter: name too long"); |
| 173 | #endif |
| 174 | if (!doingcache) |
| 175 | return; |
| 176 | /* |
| 177 | * Free the cache slot at head of lru chain. |
| 178 | */ |
| 179 | if (numcache < desiredvnodes) { |
| 180 | ncp = (struct namecache *) |
| 181 | malloc((u_long)sizeof *ncp, M_CACHE, M_WAITOK); |
| 182 | bzero((char *)ncp, sizeof *ncp); |
| 183 | numcache++; |
| 184 | } else if (ncp = nchhead) { |
| 185 | /* remove from lru chain */ |
| 186 | if (ncq = ncp->nc_nxt) |
| 187 | ncq->nc_prev = ncp->nc_prev; |
| 188 | else |
| 189 | nchtail = ncp->nc_prev; |
| 190 | *ncp->nc_prev = ncq; |
| 191 | /* remove from old hash chain, if on one */ |
| 192 | if (ncp->nc_back) { |
| 193 | if (ncq = ncp->nc_forw) |
| 194 | ncq->nc_back = ncp->nc_back; |
| 195 | *ncp->nc_back = ncq; |
| 196 | ncp->nc_forw = NULL; |
| 197 | ncp->nc_back = NULL; |
| 198 | } |
| 199 | } else |
| 200 | return; |
| 201 | /* grab the vnode we just found */ |
| 202 | ncp->nc_vp = vp; |
| 203 | if (vp) |
| 204 | ncp->nc_vpid = vp->v_id; |
| 205 | else |
| 206 | ncp->nc_vpid = 0; |
| 207 | /* fill in cache info */ |
| 208 | ncp->nc_dvp = dvp; |
| 209 | ncp->nc_dvpid = dvp->v_id; |
| 210 | ncp->nc_nlen = cnp->cn_namelen; |
| 211 | bcopy(cnp->cn_nameptr, ncp->nc_name, (unsigned)ncp->nc_nlen); |
| 212 | /* link at end of lru chain */ |
| 213 | ncp->nc_nxt = NULL; |
| 214 | ncp->nc_prev = nchtail; |
| 215 | *nchtail = ncp; |
| 216 | nchtail = &ncp->nc_nxt; |
| 217 | /* and insert on hash chain */ |
| 218 | ncpp = &nchashtbl[cnp->cn_hash & nchash]; |
| 219 | if (ncq = *ncpp) |
| 220 | ncq->nc_back = &ncp->nc_forw; |
| 221 | ncp->nc_forw = ncq; |
| 222 | ncp->nc_back = ncpp; |
| 223 | *ncpp = ncp; |
| 224 | } |
| 225 | |
| 226 | /* |
| 227 | * Name cache initialization, from vfs_init() when we are booting |
| 228 | */ |
| 229 | nchinit() |
| 230 | { |
| 231 | |
| 232 | nchtail = &nchhead; |
| 233 | nchashtbl = hashinit(desiredvnodes, M_CACHE, &nchash); |
| 234 | } |
| 235 | |
| 236 | /* |
| 237 | * Cache flush, a particular vnode; called when a vnode is renamed to |
| 238 | * hide entries that would now be invalid |
| 239 | */ |
| 240 | cache_purge(vp) |
| 241 | struct vnode *vp; |
| 242 | { |
| 243 | struct namecache *ncp, **ncpp; |
| 244 | |
| 245 | vp->v_id = ++nextvnodeid; |
| 246 | if (nextvnodeid != 0) |
| 247 | return; |
| 248 | for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) { |
| 249 | for (ncp = *ncpp; ncp; ncp = ncp->nc_forw) { |
| 250 | ncp->nc_vpid = 0; |
| 251 | ncp->nc_dvpid = 0; |
| 252 | } |
| 253 | } |
| 254 | vp->v_id = ++nextvnodeid; |
| 255 | } |
| 256 | |
| 257 | /* |
| 258 | * Cache flush, a whole filesystem; called when filesys is umounted to |
| 259 | * remove entries that would now be invalid |
| 260 | * |
| 261 | * The line "nxtcp = nchhead" near the end is to avoid potential problems |
| 262 | * if the cache lru chain is modified while we are dumping the |
| 263 | * inode. This makes the algorithm O(n^2), but do you think I care? |
| 264 | */ |
| 265 | cache_purgevfs(mp) |
| 266 | struct mount *mp; |
| 267 | { |
| 268 | register struct namecache *ncp, *nxtcp; |
| 269 | |
| 270 | for (ncp = nchhead; ncp; ncp = nxtcp) { |
| 271 | if (ncp->nc_dvp == NULL || ncp->nc_dvp->v_mount != mp) { |
| 272 | nxtcp = ncp->nc_nxt; |
| 273 | continue; |
| 274 | } |
| 275 | /* free the resources we had */ |
| 276 | ncp->nc_vp = NULL; |
| 277 | ncp->nc_dvp = NULL; |
| 278 | /* remove from old hash chain, if on one */ |
| 279 | if (ncp->nc_back) { |
| 280 | if (nxtcp = ncp->nc_forw) |
| 281 | nxtcp->nc_back = ncp->nc_back; |
| 282 | *ncp->nc_back = nxtcp; |
| 283 | ncp->nc_forw = NULL; |
| 284 | ncp->nc_back = NULL; |
| 285 | } |
| 286 | /* delete this entry from LRU chain */ |
| 287 | if (nxtcp = ncp->nc_nxt) |
| 288 | nxtcp->nc_prev = ncp->nc_prev; |
| 289 | else |
| 290 | nchtail = ncp->nc_prev; |
| 291 | *ncp->nc_prev = nxtcp; |
| 292 | /* cause rescan of list, it may have altered */ |
| 293 | /* also put the now-free entry at head of LRU */ |
| 294 | if (nxtcp = nchhead) |
| 295 | nxtcp->nc_prev = &ncp->nc_nxt; |
| 296 | else |
| 297 | nchtail = &ncp->nc_nxt; |
| 298 | nchhead = ncp; |
| 299 | ncp->nc_nxt = nxtcp; |
| 300 | ncp->nc_prev = &nchhead; |
| 301 | } |
| 302 | } |