From ab5c2dbb592fde4219fd3b2bf8d82e2299f6f9c9 Mon Sep 17 00:00:00 2001 From: rsc Date: Thu, 9 Aug 2007 19:05:00 +0000 Subject: [PATCH] Clearer namei --- fs.c | 175 ++++++++++++++++++++++++++++++++++++----------------------- 1 file changed, 106 insertions(+), 69 deletions(-) diff --git a/fs.c b/fs.c index d3d10e1..c62ce67 100644 --- a/fs.c +++ b/fs.c @@ -476,6 +476,73 @@ writei(struct inode *ip, char *addr, uint off, uint n) } } +// Skip over the next path element in path, +// saving it in *name and its length in *len. +// Return a pointer to the element after that +// (after any trailing slashes). +// Thus the caller can check whether *path=='\0' +// to see whether the name just removed was +// the last one. +// If there is no name to remove, return 0. +// +// Examples: +// skipelem("a/bb/c") = "bb/c", with *name = "a/bb/c", len=1 +// skipelem("///a/bb") = "b", with *name="a/bb", len=1 +// skipelem("") = skipelem("////") = 0 +// +static char* +skipelem(char *path, char **name, int *len) +{ + while(*path == '/') + path++; + if(*path == 0) + return 0; + *name = path; + while(*path != '/' && *path != 0) + path++; + *len = path - *name; + while(*path == '/') + path++; + return path; +} + +// Look for a directory entry in a directory. +// If not found, return -1. +// If found: +// set *poff to the byte offset of the directory entry +// set *pinum to the inode number +// return 0. +static int +lookup(struct inode *dp, char *name, int namelen, uint *poff, uint *pinum) +{ + uint off; + struct buf *bp; + struct dirent *de; + + if(dp->type != T_DIR) + return -1; + + for(off = 0; off < dp->size; off += BSIZE){ + bp = bread(dp->dev, bmap(dp, off / BSIZE)); + for(de = (struct dirent*) bp->data; + de < (struct dirent*) (bp->data + BSIZE); + de++){ + if(de->inum == 0) + continue; + if(memcmp(name, de->name, namelen) == 0 && + (namelen == DIRSIZ || de->name[namelen]== 0)){ + // entry matches path element + *poff = off + (uchar*)de - bp->data; + *pinum = de->inum; + brelse(bp); + return 0; + } + } + brelse(bp); + } + return -1; +} + // look up a path name, in one of three modes. // NAMEI_LOOKUP: return locked target inode. // NAMEI_CREATE: return locked parent inode. @@ -491,12 +558,10 @@ namei(char *path, int mode, uint *ret_off, { struct inode *dp; struct proc *p = curproc[cpu()]; - char *cp = path, *cp1; + char *name; + int namelen; uint off, dev; - struct buf *bp; - struct dirent *ep; - int i, l, atend; - uint ninum; + uint inum; if(ret_off) *ret_off = 0xffffffff; @@ -505,91 +570,57 @@ namei(char *path, int mode, uint *ret_off, if(ret_ip) *ret_ip = 0; - if(*cp == '/') + if(*path == '/') dp = iget(rootdev, 1); else { dp = iincref(p->cwd); ilock(dp); } - for(;;){ - while(*cp == '/') - cp++; + while((path = skipelem(path, &name, &namelen)) != 0){ + // Truncate names in path to DIRSIZ chars. + if(namelen > DIRSIZ) + namelen = DIRSIZ; - if(*cp == '\0'){ - if(mode == NAMEI_LOOKUP) + if(dp->type != T_DIR) + goto fail; + + if(lookup(dp, name, namelen, &off, &inum) < 0){ + if(mode == NAMEI_CREATE && *path == '\0'){ + *ret_last = name; return dp; - if(mode == NAMEI_CREATE && ret_ip){ - *ret_ip = dp; - return 0; } - iput(dp); - return 0; + goto fail; } - if(dp->type != T_DIR){ - iput(dp); - return 0; - } - - for(i = 0; cp[i] != 0 && cp[i] != '/'; i++) - ; - l = i; - if(i > DIRSIZ) - l = DIRSIZ; - - for(off = 0; off < dp->size; off += BSIZE){ - bp = bread(dp->dev, bmap(dp, off / BSIZE)); - for(ep = (struct dirent*) bp->data; - ep < (struct dirent*) (bp->data + BSIZE); - ep++){ - if(ep->inum == 0) - continue; - if(memcmp(cp, ep->name, l) == 0 && - (l == DIRSIZ || ep->name[l]== 0)){ - // entry matches path element - off += (uchar*)ep - bp->data; - ninum = ep->inum; - brelse(bp); - cp += i; - goto found; - } - } - brelse(bp); - } - atend = 1; - for(cp1 = cp; *cp1; cp1++) - if(*cp1 == '/') - atend = 0; - if(mode == NAMEI_CREATE && atend){ - if(*cp == '\0'){ - iput(dp); - return 0; - } - *ret_last = cp; - return dp; - } - - iput(dp); - return 0; - - found: - if(mode == NAMEI_DELETE && *cp == '\0'){ + if(mode == NAMEI_DELETE && *path == '\0'){ // can't unlink . and .. - if((i == 1 && memcmp(cp-1, ".", 1) == 0) || - (i == 2 && memcmp(cp-2, "..", 2) == 0)){ - iput(dp); - return 0; + if((namelen == 1 && memcmp(name, ".", 1) == 0) || + (namelen == 2 && memcmp(name, "..", 2) == 0)){ + goto fail; } *ret_off = off; return dp; } + dev = dp->dev; iput(dp); - dp = iget(dev, ninum); + dp = iget(dev, inum); if(dp->type == 0 || dp->nlink < 1) panic("namei"); } + + if(mode == NAMEI_LOOKUP) + return dp; + if(mode == NAMEI_CREATE && ret_ip){ + *ret_ip = dp; + return 0; + } + goto fail; + +fail: + iput(dp); + return 0; } // Write a new directory entry (name, ino) into the directory dp. @@ -675,6 +706,12 @@ unlink(char *cp) if(readi(dp, (char*)&de, off, sizeof(de)) != sizeof(de) || de.inum == 0) panic("unlink no entry"); + + // Cannot remove "." or ".." - the 2 and 3 count the trailing NUL. + if(memcmp(de.name, ".", 2) == 0 || memcmp(de.name, "..", 3) == 0){ + iput(dp); + return -1; + } inum = de.inum;