Clearer namei
This commit is contained in:
rsc
parent
806f4c11f7
commit
ab5c2dbb59
1 changed files with 106 additions and 69 deletions
175
fs.c
175
fs.c
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@ -476,6 +476,73 @@ writei(struct inode *ip, char *addr, uint off, uint n)
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}
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}
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// Skip over the next path element in path,
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// saving it in *name and its length in *len.
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// Return a pointer to the element after that
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// (after any trailing slashes).
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// Thus the caller can check whether *path=='\0'
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// to see whether the name just removed was
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// the last one.
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// If there is no name to remove, return 0.
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//
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// Examples:
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// skipelem("a/bb/c") = "bb/c", with *name = "a/bb/c", len=1
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// skipelem("///a/bb") = "b", with *name="a/bb", len=1
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// skipelem("") = skipelem("////") = 0
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//
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static char*
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skipelem(char *path, char **name, int *len)
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{
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while(*path == '/')
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path++;
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if(*path == 0)
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return 0;
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*name = path;
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while(*path != '/' && *path != 0)
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path++;
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*len = path - *name;
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while(*path == '/')
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path++;
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return path;
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}
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// Look for a directory entry in a directory.
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// If not found, return -1.
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// If found:
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// set *poff to the byte offset of the directory entry
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// set *pinum to the inode number
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// return 0.
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static int
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lookup(struct inode *dp, char *name, int namelen, uint *poff, uint *pinum)
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{
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uint off;
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struct buf *bp;
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struct dirent *de;
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if(dp->type != T_DIR)
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return -1;
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for(off = 0; off < dp->size; off += BSIZE){
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bp = bread(dp->dev, bmap(dp, off / BSIZE));
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for(de = (struct dirent*) bp->data;
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de < (struct dirent*) (bp->data + BSIZE);
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de++){
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if(de->inum == 0)
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continue;
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if(memcmp(name, de->name, namelen) == 0 &&
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(namelen == DIRSIZ || de->name[namelen]== 0)){
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// entry matches path element
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*poff = off + (uchar*)de - bp->data;
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*pinum = de->inum;
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brelse(bp);
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return 0;
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}
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}
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brelse(bp);
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}
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return -1;
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}
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// look up a path name, in one of three modes.
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// NAMEI_LOOKUP: return locked target inode.
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// NAMEI_CREATE: return locked parent inode.
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@ -491,12 +558,10 @@ namei(char *path, int mode, uint *ret_off,
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{
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struct inode *dp;
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struct proc *p = curproc[cpu()];
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char *cp = path, *cp1;
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char *name;
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int namelen;
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uint off, dev;
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struct buf *bp;
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struct dirent *ep;
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int i, l, atend;
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uint ninum;
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uint inum;
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if(ret_off)
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*ret_off = 0xffffffff;
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@ -505,91 +570,57 @@ namei(char *path, int mode, uint *ret_off,
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if(ret_ip)
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*ret_ip = 0;
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if(*cp == '/')
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if(*path == '/')
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dp = iget(rootdev, 1);
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else {
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dp = iincref(p->cwd);
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ilock(dp);
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}
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for(;;){
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while(*cp == '/')
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cp++;
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while((path = skipelem(path, &name, &namelen)) != 0){
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// Truncate names in path to DIRSIZ chars.
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if(namelen > DIRSIZ)
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namelen = DIRSIZ;
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if(*cp == '\0'){
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if(mode == NAMEI_LOOKUP)
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if(dp->type != T_DIR)
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goto fail;
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if(lookup(dp, name, namelen, &off, &inum) < 0){
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if(mode == NAMEI_CREATE && *path == '\0'){
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*ret_last = name;
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return dp;
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if(mode == NAMEI_CREATE && ret_ip){
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*ret_ip = dp;
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return 0;
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}
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iput(dp);
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return 0;
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goto fail;
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}
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if(dp->type != T_DIR){
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iput(dp);
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return 0;
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}
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for(i = 0; cp[i] != 0 && cp[i] != '/'; i++)
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;
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l = i;
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if(i > DIRSIZ)
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l = DIRSIZ;
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for(off = 0; off < dp->size; off += BSIZE){
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bp = bread(dp->dev, bmap(dp, off / BSIZE));
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for(ep = (struct dirent*) bp->data;
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ep < (struct dirent*) (bp->data + BSIZE);
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ep++){
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if(ep->inum == 0)
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continue;
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if(memcmp(cp, ep->name, l) == 0 &&
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(l == DIRSIZ || ep->name[l]== 0)){
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// entry matches path element
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off += (uchar*)ep - bp->data;
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ninum = ep->inum;
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brelse(bp);
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cp += i;
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goto found;
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}
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}
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brelse(bp);
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}
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atend = 1;
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for(cp1 = cp; *cp1; cp1++)
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if(*cp1 == '/')
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atend = 0;
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if(mode == NAMEI_CREATE && atend){
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if(*cp == '\0'){
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iput(dp);
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return 0;
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}
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*ret_last = cp;
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return dp;
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}
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iput(dp);
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return 0;
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found:
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if(mode == NAMEI_DELETE && *cp == '\0'){
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if(mode == NAMEI_DELETE && *path == '\0'){
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// can't unlink . and ..
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if((i == 1 && memcmp(cp-1, ".", 1) == 0) ||
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(i == 2 && memcmp(cp-2, "..", 2) == 0)){
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iput(dp);
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return 0;
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if((namelen == 1 && memcmp(name, ".", 1) == 0) ||
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(namelen == 2 && memcmp(name, "..", 2) == 0)){
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goto fail;
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}
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*ret_off = off;
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return dp;
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}
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dev = dp->dev;
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iput(dp);
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dp = iget(dev, ninum);
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dp = iget(dev, inum);
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if(dp->type == 0 || dp->nlink < 1)
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panic("namei");
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}
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if(mode == NAMEI_LOOKUP)
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return dp;
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if(mode == NAMEI_CREATE && ret_ip){
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*ret_ip = dp;
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return 0;
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}
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goto fail;
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fail:
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iput(dp);
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return 0;
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}
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// Write a new directory entry (name, ino) into the directory dp.
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@ -675,6 +706,12 @@ unlink(char *cp)
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if(readi(dp, (char*)&de, off, sizeof(de)) != sizeof(de) || de.inum == 0)
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panic("unlink no entry");
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// Cannot remove "." or ".." - the 2 and 3 count the trailing NUL.
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if(memcmp(de.name, ".", 2) == 0 || memcmp(de.name, "..", 3) == 0){
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iput(dp);
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return -1;
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}
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inum = de.inum;
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