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Annotation of Net2/isofs/isofs_lookup.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1989 The Regents of the University of California.
        !             3:  * 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:  *     @(#)ufs_lookup.c        7.33 (Berkeley) 5/19/91
        !            34:  */
        !            35: 
        !            36: #include "param.h"
        !            37: #include "namei.h"
        !            38: #include "buf.h"
        !            39: #include "file.h"
        !            40: #include "vnode.h"
        !            41: #include "mount.h"
        !            42: 
        !            43: #include "iso.h"
        !            44: #include "isofs_node.h"
        !            45: 
        !            46: struct nchstats nchstats;
        !            47: 
        !            48: /*
        !            49:  * Convert a component of a pathname into a pointer to a locked inode.
        !            50:  * This is a very central and rather complicated routine.
        !            51:  * If the file system is not maintained in a strict tree hierarchy,
        !            52:  * this can result in a deadlock situation (see comments in code below).
        !            53:  *
        !            54:  * The flag argument is LOOKUP, CREATE, RENAME, or DELETE depending on
        !            55:  * whether the name is to be looked up, created, renamed, or deleted.
        !            56:  * When CREATE, RENAME, or DELETE is specified, information usable in
        !            57:  * creating, renaming, or deleting a directory entry may be calculated.
        !            58:  * If flag has LOCKPARENT or'ed into it and the target of the pathname
        !            59:  * exists, lookup returns both the target and its parent directory locked.
        !            60:  * When creating or renaming and LOCKPARENT is specified, the target may
        !            61:  * not be ".".  When deleting and LOCKPARENT is specified, the target may
        !            62:  * be "."., but the caller must check to ensure it does an vrele and iput
        !            63:  * instead of two iputs.
        !            64:  *
        !            65:  * Overall outline of ufs_lookup:
        !            66:  *
        !            67:  *     check accessibility of directory
        !            68:  *     look for name in cache, if found, then if at end of path
        !            69:  *       and deleting or creating, drop it, else return name
        !            70:  *     search for name in directory, to found or notfound
        !            71:  * notfound:
        !            72:  *     if creating, return locked directory, leaving info on available slots
        !            73:  *     else return error
        !            74:  * found:
        !            75:  *     if at end of path and deleting, return information to allow delete
        !            76:  *     if at end of path and rewriting (RENAME and LOCKPARENT), lock target
        !            77:  *       inode and return info to allow rewrite
        !            78:  *     if not at end, add name to cache; if at end and neither creating
        !            79:  *       nor deleting, add name to cache
        !            80:  *
        !            81:  * NOTE: (LOOKUP | LOCKPARENT) currently returns the parent inode unlocked.
        !            82:  */
        !            83: isofs_lookup(vdp, ndp, p)
        !            84:        register struct vnode *vdp;
        !            85:        register struct nameidata *ndp;
        !            86:        struct proc *p;
        !            87: {
        !            88:        register struct iso_node *dp;   /* the directory we are searching */
        !            89:        register struct iso_mnt *imp;   /* file system that directory is in */
        !            90:        struct buf *bp = 0;             /* a buffer of directory entries */
        !            91:        register struct iso_directory_record *ep;
        !            92:                                        /* the current directory entry */
        !            93:        int entryoffsetinblock;         /* offset of ep in bp's buffer */
        !            94:        enum {NONE, COMPACT, FOUND} slotstatus;
        !            95:        int slotoffset = -1;            /* offset of area with free space */
        !            96:        int slotsize;                   /* size of area at slotoffset */
        !            97:        int slotfreespace;              /* amount of space free in slot */
        !            98:        int slotneeded;                 /* size of the entry we're seeking */
        !            99:        int numdirpasses;               /* strategy for directory search */
        !           100:        int endsearch;                  /* offset to end directory search */
        !           101:        struct iso_node *pdp;           /* saved dp during symlink work */
        !           102:        struct iso_node *tdp;           /* returned by iget */
        !           103:        int flag;                       /* LOOKUP, CREATE, RENAME, or DELETE */
        !           104:        int lockparent;                 /* 1 => lockparent flag is set */
        !           105:        int wantparent;                 /* 1 => wantparent or lockparent flag */
        !           106:        int error;
        !           107: 
        !           108:        int reclen;
        !           109:        int namelen;
        !           110: 
        !           111:        ndp->ni_dvp = vdp;
        !           112:        ndp->ni_vp = NULL;
        !           113:        dp = VTOI(vdp);
        !           114:        imp = dp->i_mnt;
        !           115:        lockparent = ndp->ni_nameiop & LOCKPARENT;
        !           116:        flag = ndp->ni_nameiop & OPMASK;
        !           117:        wantparent = ndp->ni_nameiop & (LOCKPARENT|WANTPARENT);
        !           118: 
        !           119:        /*
        !           120:         * Check accessiblity of directory.
        !           121:         */
        !           122:        if ((dp->iso_flags & 2) == 0)
        !           123:                return (ENOTDIR);
        !           124: 
        !           125:        /*
        !           126:         * We now have a segment name to search for, and a directory to search.
        !           127:         *
        !           128:         * Before tediously performing a linear scan of the directory,
        !           129:         * check the name cache to see if the directory/name pair
        !           130:         * we are looking for is known already.
        !           131:         */
        !           132:        if (error = cache_lookup(ndp)) {
        !           133:                int vpid;       /* capability number of vnode */
        !           134: 
        !           135:                if (error == ENOENT)
        !           136:                        return (error);
        !           137: #ifdef PARANOID
        !           138:                if (vdp == ndp->ni_rdir && ndp->ni_isdotdot)
        !           139:                        panic("ufs_lookup: .. through root");
        !           140: #endif
        !           141:                /*
        !           142:                 * Get the next vnode in the path.
        !           143:                 * See comment below starting `Step through' for
        !           144:                 * an explaination of the locking protocol.
        !           145:                 */
        !           146:                pdp = dp;
        !           147:                dp = VTOI(ndp->ni_vp);
        !           148:                vdp = ndp->ni_vp;
        !           149:                vpid = vdp->v_id;
        !           150:                if (pdp == dp) {
        !           151:                        VREF(vdp);
        !           152:                        error = 0;
        !           153:                } else if (ndp->ni_isdotdot) {
        !           154:                        ISO_IUNLOCK(pdp);
        !           155:                        error = vget(vdp);
        !           156:                        if (!error && lockparent && *ndp->ni_next == '\0')
        !           157:                                ISO_ILOCK(pdp);
        !           158:                } else {
        !           159:                        error = vget(vdp);
        !           160:                        if (!lockparent || error || *ndp->ni_next != '\0')
        !           161:                                ISO_IUNLOCK(pdp);
        !           162:                }
        !           163:                /*
        !           164:                 * Check that the capability number did not change
        !           165:                 * while we were waiting for the lock.
        !           166:                 */
        !           167:                if (!error) {
        !           168:                        if (vpid == vdp->v_id)
        !           169:                                return (0);
        !           170:                        iso_iput(dp);
        !           171:                        if (lockparent && pdp != dp && *ndp->ni_next == '\0')
        !           172:                                ISO_IUNLOCK(pdp);
        !           173:                }
        !           174:                ISO_ILOCK(pdp);
        !           175:                dp = pdp;
        !           176:                vdp = ITOV(dp);
        !           177:                ndp->ni_vp = NULL;
        !           178:        }
        !           179: 
        !           180:        /*
        !           181:         * If there is cached information on a previous search of
        !           182:         * this directory, pick up where we last left off.
        !           183:         * We cache only lookups as these are the most common
        !           184:         * and have the greatest payoff. Caching CREATE has little
        !           185:         * benefit as it usually must search the entire directory
        !           186:         * to determine that the entry does not exist. Caching the
        !           187:         * location of the last DELETE or RENAME has not reduced
        !           188:         * profiling time and hence has been removed in the interest
        !           189:         * of simplicity.
        !           190:         */
        !           191:        if (flag != LOOKUP || dp->i_diroff == 0 || dp->i_diroff > dp->i_size) {
        !           192:                ndp->ni_ufs.ufs_offset = 0;
        !           193:                numdirpasses = 1;
        !           194:        } else {
        !           195:                ndp->ni_ufs.ufs_offset = dp->i_diroff;
        !           196:                entryoffsetinblock = iso_blkoff(imp, ndp->ni_ufs.ufs_offset);
        !           197:                if (entryoffsetinblock != 0) {
        !           198:                        if (error = iso_blkatoff(dp, ndp->ni_ufs.ufs_offset,
        !           199:                            (char **)0, &bp))
        !           200:                                return (error);
        !           201:                }
        !           202:                numdirpasses = 2;
        !           203:                nchstats.ncs_2passes++;
        !           204:        }
        !           205:        endsearch = roundup(dp->i_size, imp->logical_block_size);
        !           206: 
        !           207: searchloop:
        !           208:        while (ndp->ni_ufs.ufs_offset < endsearch) {
        !           209:                /*
        !           210:                 * If offset is on a block boundary,
        !           211:                 * read the next directory block.
        !           212:                 * Release previous if it exists.
        !           213:                 */
        !           214:                if (iso_blkoff(imp, ndp->ni_ufs.ufs_offset) == 0) {
        !           215:                        if (bp != NULL)
        !           216:                                brelse(bp);
        !           217:                        if (error = iso_blkatoff(dp, ndp->ni_ufs.ufs_offset,
        !           218:                                                 (char **)0, &bp))
        !           219:                                return (error);
        !           220:                        entryoffsetinblock = 0;
        !           221:                }
        !           222:                /*
        !           223:                 * Get pointer to next entry.
        !           224:                 */
        !           225: 
        !           226:                ep = (struct iso_directory_record *)
        !           227:                        (bp->b_un.b_addr + entryoffsetinblock);
        !           228: 
        !           229:                reclen = isonum_711 (ep->length);
        !           230:                if (reclen == 0) {
        !           231:                        /* skip to next block, if any */
        !           232:                        ndp->ni_ufs.ufs_offset =
        !           233:                                roundup (ndp->ni_ufs.ufs_offset,
        !           234:                                         imp->logical_block_size);
        !           235:                        continue;
        !           236:                }
        !           237: 
        !           238:                if (reclen < sizeof (struct iso_directory_record))
        !           239:                        /* illegal entry, stop */
        !           240:                        break;
        !           241: 
        !           242:                if (entryoffsetinblock + reclen >= imp->logical_block_size)
        !           243:                        /* entries are not allowed to cross boundaries */
        !           244:                        break;
        !           245: 
        !           246:                /*
        !           247:                 * Check for a name match.
        !           248:                 */
        !           249:                namelen = isonum_711 (ep->name_len);
        !           250: 
        !           251:                if (reclen < sizeof (struct iso_directory_record) + namelen)
        !           252:                        /* illegal entry, stop */
        !           253:                        break;
        !           254: 
        !           255:                if ((namelen == 1
        !           256:                     && ((ndp->ni_namelen == 1
        !           257:                          && ndp->ni_ptr[0] == '.'
        !           258:                          && ep->name[0] == 0)
        !           259:                         || (ndp->ni_isdotdot && ep->name[0] == 1)))
        !           260:                    || (namelen >= ndp->ni_namelen
        !           261:                        && isofncmp(ndp->ni_ptr, ndp->ni_namelen, ep->name,
        !           262:                                namelen))) {
        !           263:                        /*
        !           264:                         * Save directory entry's inode number and
        !           265:                         * reclen in ndp->ni_ufs area, and release
        !           266:                         * directory buffer.
        !           267:                         */
        !           268:                        ndp->ni_ufs.ufs_ino = isonum_733 (ep->extent);
        !           269:                        brelse(bp);
        !           270:                        goto found;
        !           271:                }
        !           272:                ndp->ni_ufs.ufs_offset += reclen;
        !           273:                entryoffsetinblock += reclen;
        !           274:        }
        !           275: /* notfound: */
        !           276:        /*
        !           277:         * If we started in the middle of the directory and failed
        !           278:         * to find our target, we must check the beginning as well.
        !           279:         */
        !           280:        if (numdirpasses == 2) {
        !           281:                numdirpasses--;
        !           282:                ndp->ni_ufs.ufs_offset = 0;
        !           283:                endsearch = dp->i_diroff;
        !           284:                goto searchloop;
        !           285:        }
        !           286:        if (bp != NULL)
        !           287:                brelse(bp);
        !           288:        /*
        !           289:         * Insert name into cache (as non-existent) if appropriate.
        !           290:         */
        !           291:        if (ndp->ni_makeentry)
        !           292:                cache_enter(ndp);
        !           293:        return (ENOENT);
        !           294: 
        !           295: found:
        !           296:        if (numdirpasses == 2)
        !           297:                nchstats.ncs_pass2++;
        !           298: 
        !           299:        /*
        !           300:         * Found component in pathname.
        !           301:         * If the final component of path name, save information
        !           302:         * in the cache as to where the entry was found.
        !           303:         */
        !           304:        if (*ndp->ni_next == '\0' && flag == LOOKUP)
        !           305:                dp->i_diroff = ndp->ni_ufs.ufs_offset
        !           306:                        &~ (imp->logical_block_size - 1);
        !           307: 
        !           308:        /*
        !           309:         * Step through the translation in the name.  We do not `iput' the
        !           310:         * directory because we may need it again if a symbolic link
        !           311:         * is relative to the current directory.  Instead we save it
        !           312:         * unlocked as "pdp".  We must get the target inode before unlocking
        !           313:         * the directory to insure that the inode will not be removed
        !           314:         * before we get it.  We prevent deadlock by always fetching
        !           315:         * inodes from the root, moving down the directory tree. Thus
        !           316:         * when following backward pointers ".." we must unlock the
        !           317:         * parent directory before getting the requested directory.
        !           318:         * There is a potential race condition here if both the current
        !           319:         * and parent directories are removed before the `iget' for the
        !           320:         * inode associated with ".." returns.  We hope that this occurs
        !           321:         * infrequently since we cannot avoid this race condition without
        !           322:         * implementing a sophisticated deadlock detection algorithm.
        !           323:         * Note also that this simple deadlock detection scheme will not
        !           324:         * work if the file system has any hard links other than ".."
        !           325:         * that point backwards in the directory structure.
        !           326:         */
        !           327:        pdp = dp;
        !           328:        if (ndp->ni_isdotdot) {
        !           329:                ISO_IUNLOCK(pdp);       /* race to get the inode */
        !           330:                if (error = iso_iget(dp, ndp->ni_ufs.ufs_ino, &tdp, ep)) {
        !           331:                        ISO_ILOCK(pdp);
        !           332:                        return (error);
        !           333:                }
        !           334:                if (lockparent && *ndp->ni_next == '\0')
        !           335:                        ISO_ILOCK(pdp);
        !           336:                ndp->ni_vp = ITOV(tdp);
        !           337:        } else if (dp->i_number == ndp->ni_ufs.ufs_ino) {
        !           338:                VREF(vdp);      /* we want ourself, ie "." */
        !           339:                ndp->ni_vp = vdp;
        !           340:        } else {
        !           341:                if (error = iso_iget(dp, ndp->ni_ufs.ufs_ino, &tdp, ep))
        !           342:                        return (error);
        !           343:                if (!lockparent || *ndp->ni_next != '\0')
        !           344:                        ISO_IUNLOCK(pdp);
        !           345:                ndp->ni_vp = ITOV(tdp);
        !           346:        }
        !           347: 
        !           348:        /*
        !           349:         * Insert name into cache if appropriate.
        !           350:         */
        !           351:        if (ndp->ni_makeentry)
        !           352:                cache_enter(ndp);
        !           353:        return (0);
        !           354: }
        !           355: 
        !           356: 
        !           357: /*
        !           358:  * Return buffer with contents of block "offset"
        !           359:  * from the beginning of directory "ip".  If "res"
        !           360:  * is non-zero, fill it in with a pointer to the
        !           361:  * remaining space in the directory.
        !           362:  */
        !           363: iso_blkatoff(ip, offset, res, bpp)
        !           364:        struct iso_node *ip;
        !           365:        off_t offset;
        !           366:        char **res;
        !           367:        struct buf **bpp;
        !           368: {
        !           369:        register struct iso_mnt *imp = ip->i_mnt;
        !           370:        daddr_t lbn = iso_lblkno (imp, offset);
        !           371:        int bsize = iso_blksize (imp, ip, lbn);
        !           372:        struct buf *bp;
        !           373:        int error;
        !           374: 
        !           375:        *bpp = 0;
        !           376:        if (error = bread(ITOV(ip), lbn, bsize, NOCRED, &bp)) {
        !           377:                brelse(bp);
        !           378:                return (error);
        !           379:        }
        !           380:        if (res)
        !           381:                *res = bp->b_un.b_addr + iso_blkoff(imp, offset);
        !           382:        *bpp = bp;
        !           383: 
        !           384:        return (0);
        !           385: }
        !           386: 
        !           387: 

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