namei returns locked parent dir inode for create / unlink

don't hold fd table lock across idecref() (latter does block i/o)
idecref calls iput() in case last ref -> freeing inode
dir size is 512 * # blocks, so readi/writei &c work
unlink deletes dirent even if ip->nlink > 0

Notes

@@ -365,3 +365,18 @@ two bugs in unlink: don't just return if nlink > 0,
   and search for name, not inum
 is there a create/create race for same file name?
   resulting in two entries w/ same name in directory?
+
+namei
+  return just inode
+  return offset in dir where found, w/ dir locked, for unlink
+  return dir locked, for mknod
+
+is the offset alone useful? how do I read/write it?
+
+test: one process unlinks a file while another links to it
+test: simultaneous create of same file
+test: one process opens a file while another deletes it
+
+oy, mkfs wants dir size to be last written entry, but i
+  want it to be nblocks*512
+  maybe fix kernel code to handle former

defs.h

@@ -116,7 +116,7 @@ void ilock(struct inode *ip);
 void iunlock(struct inode *ip);
 void idecref(struct inode *ip);
 void iput(struct inode *ip);
-struct inode * namei(char *path, uint *);
+struct inode * namei(char *path, int, uint *);
 void stati(struct inode *ip, struct stat *st);
 int readi(struct inode *ip, char *xdst, uint off, uint n);
 int writei(struct inode *ip, char *addr, uint off, uint n);

fd.c

@@ -108,18 +108,22 @@ fd_close(struct fd *fd)
     panic("fd_close");
 
   if(--fd->ref == 0){
-    if(fd->type == FD_PIPE){
+    struct fd dummy = *fd;
-      pipe_close(fd->pipe, fd->writeable);
+
-    } else if(fd->type == FD_FILE){
+    fd->ref = 0;
-      idecref(fd->ip);
+    fd->type = FD_CLOSED;
+    release(&fd_table_lock);
+
+    if(dummy.type == FD_PIPE){
+      pipe_close(dummy.pipe, dummy.writeable);
+    } else if(dummy.type == FD_FILE){
+      idecref(dummy.ip);
     } else {
       panic("fd_close");
     }
-    fd->ref = 0;
+  } else {
-    fd->type = FD_CLOSED;
+    release(&fd_table_lock);
   }
-  
-  release(&fd_table_lock);
 }
 
 int

fs.c

@@ -286,14 +286,8 @@ iput(struct inode *ip)
 void
 idecref(struct inode *ip)
 {
-  acquire(&inode_table_lock);
+  ilock(ip);
-
+  iput(ip);
-  if(ip->count < 1)
-    panic("idecref");
-
-  ip->count -= 1;
-
-  release(&inode_table_lock);
 }
 
 void
@@ -376,34 +370,37 @@ writei(struct inode *ip, char *addr, uint off, uint n)
   }
 }
 
+// look up a path name, in one of three modes.
+// NAMEI_LOOKUP: return locked target inode.
+// NAMEI_CREATE: return locked parent inode.
+//   but return 0 if name does exist.
+// NAMEI_DELETE: return locked parent inode, offset of dirent in *ret_off.
+//   return 0 if name doesn't exist.
 struct inode *
-namei(char *path, uint *ret_pinum)
+namei(char *path, int mode, uint *ret_off)
 {
   struct inode *dp;
-  char *cp = path;
+  char *cp = path, *cp1;
   uint off, dev;
   struct buf *bp;
   struct dirent *ep;
-  int i;
+  int i, atend;
   unsigned ninum;
-  unsigned pinum;
   
   dp = iget(rootdev, 1);
-  pinum = dp->inum;
 
   while(*cp == '/')
     cp++;
 
   while(1){
-    if(*cp == '\0') {
+    if(*cp == '\0'){
-      if (ret_pinum)
+      if(mode == NAMEI_LOOKUP)
-	*ret_pinum = pinum;
+        return dp;
-      return dp;
+      iput(dp);
+      return 0;
     }
 
     if(dp->type != T_DIR){
-      if (ret_pinum)
-	*ret_pinum = pinum;
       iput(dp);
       return 0;
     }
@@ -419,6 +416,7 @@ namei(char *path, uint *ret_pinum)
           if(cp[i] != ep->name[i])
             break;
         if((cp[i] == '\0' || cp[i] == '/') && (i >= DIRSIZ || ep->name[i] == '\0')){
+          off += (uchar*)ep - bp->data;
           ninum = ep->inum;
           brelse(bp);
           cp += i;
@@ -427,14 +425,22 @@ namei(char *path, uint *ret_pinum)
       }
       brelse(bp);
     }
+    atend = 1;
+    for(cp1 = cp; *cp1; cp1++)
+      if(*cp1 == '/')
+        atend = 0;
+    if(mode == NAMEI_CREATE && atend)
+      return dp;
+
     iput(dp);
-    if (ret_pinum)
-      *ret_pinum = pinum;
     return 0;
 
   found:
+    if(mode == NAMEI_DELETE && *cp == '\0'){
+      *ret_off = off;
+      return dp;
+    }
     dev = dp->dev;
-    pinum = dp->inum;
     iput(dp);
     dp = iget(dev, ninum);
     if(dp->type == 0 || dp->nlink < 1)
@@ -453,6 +459,9 @@ wdir(struct inode *dp, char *name, uint ino)
   int i;
   int lb;
 
+  if(dp->size % BSIZE)
+    dp->size += (BSIZE - dp->size % BSIZE);
+
   for(off = 0; off < dp->size; off += BSIZE) {
     bp = bread(dp->dev, bmap(dp, off / BSIZE));
     for(ep = (struct dirent *) bp->data;
@@ -469,14 +478,16 @@ wdir(struct inode *dp, char *name, uint ino)
   }
   dp->addrs[lb] = balloc(dp->dev);
   bp = bread(dp->dev, dp->addrs[lb]);
+  memset(bp->data, 0, BSIZE);
   ep = (struct dirent *) (bp->data);
+  dp->size += BSIZE;
+
  found:
   ep->inum = ino;
   for(i = 0; i < DIRSIZ && name[i]; i++)
     ep->name[i] = name[i];
   for( ; i < DIRSIZ; i++)
     ep->name[i] = '\0';
-  dp->size += sizeof(struct dirent);
   bwrite (bp, bmap(dp, off/BSIZE));   // write directory block
   brelse(bp);
   iupdate(dp);
@@ -486,15 +497,12 @@ struct inode *
 mknod(char *cp, short type, short major, short minor)
 {
   struct inode *ip, *dp;
-  uint pinum = 0;
 
   cprintf("mknod: %s %d %d %d\n", cp, type, major, minor);
 
-  if ((ip = namei(cp, &pinum)) != 0) {
+  if ((dp = namei(cp, NAMEI_CREATE, 0)) == 0)
-    iput(ip);
     return 0;
-  }
+
-  dp = iget(rootdev, pinum);
   ip = ialloc(dp->dev, type);
   if (ip == 0) {
     iput(dp);
@@ -515,74 +523,81 @@ mknod(char *cp, short type, short major, short minor)
 int
 unlink(char *cp)
 {
-  struct inode *ip;
+  struct inode *ip, *dp;
-  struct inode *dp;
+  struct dirent de;
-  struct dirent *ep = 0;
+  uint off, inum, cc;
-  int off;
-  struct buf *bp = 0;
-  uint pinum;
   
+  cprintf("unlink(%s)\n", cp);
 
-  if ((ip = namei(cp, &pinum)) == 0) {
+  if ((dp = namei(cp, NAMEI_DELETE, &off)) == 0) {
     cprintf("unlink(%s) it doesn't exist\n", cp);
     return -1;
   }
 
-  ip->nlink--;
+  if((cc = readi(dp, (char*)&de, off, sizeof(de))) != sizeof(de) ||
-  if (ip->nlink > 0) {
+     de.inum == 0){
-    iput(ip);
+    cprintf("off %d dp->size %d cc %d de.inum %d",
-    return 0;
+            off, dp->size, cc, de.inum);
+    panic("unlink no entry");
   }
+  inum = de.inum;
+  cprintf("dinum %d off %d de %s/%d\n", 
+          dp->inum, off, de.name, de.inum);
 
-  dp = iget(rootdev, pinum);
+  memset(&de, 0, sizeof(de));
-  for(off = 0; off < dp->size; off += BSIZE) {
+  if(writei(dp, (char*)&de, off, sizeof(de)) != sizeof(de))
-    bp = bread(dp->dev, bmap(dp, off / BSIZE));
+    panic("unlink dir write");
-    for(ep = (struct dirent *) bp->data;
-	ep < (struct dirent *) (bp->data + BSIZE);
-	ep++){
-      if(ep->inum == ip->inum) {
-	goto found;
-      }
-    }
-    brelse(bp);
-  }
-  panic("unlink: entry doesn't exist\n");
 
- found:
+  iupdate(dp);
-  ep->inum = 0;
-  memset(ep->name, '\0', DIRSIZ);
-  bwrite (bp, bmap(dp, off/BSIZE));   // write directory block
-  brelse(bp);
-  dp->size -= sizeof(struct dirent);
-  iupdate (dp);
   iput(dp);
+
+  ip = iget(dp->dev, inum);
+  if(ip == 0)
+    panic("unlink no inode");
+
+  ip->nlink--;
+
+  iupdate(ip);
   iput(ip);
+
   return 0;
 }
 
 int
 link(char *name1, char *name2)
 {
-  struct inode *ip, *dp, *xip;
+  struct inode *ip, *dp;
-  uint pinum = 0;
 
   cprintf("link(%s, %s)\n", name1, name2);
 
-  if ((xip = namei(name2, &pinum)) != 0) {
+  if ((ip = namei(name1, NAMEI_LOOKUP, 0)) == 0){
-    cprintf("  failed %s exists\n", name2);
-    iput(xip);
-    return -1;
-  }
-
-  if ((ip = namei(name1, &pinum)) == 0){
     cprintf("  failed %s does not exist\n", name1);
     return -1;
   }
+  if(ip->type == T_DIR){
+    cprintf("  failed %s is a dir\n", name1);
+    iput(ip);
+    return -1;
+  }
 
+  iunlock(ip);
+
+  if ((dp = namei(name2, NAMEI_CREATE, 0)) == 0) {
+    cprintf("  failed %s exists\n", name2);
+    idecref(ip);
+    return -1;
+  }
+  if(dp->dev != ip->dev){
+    cprintf("  cross-device link\n");
+    idecref(ip);
+    iput(dp);
+    return -1;
+  }
+  
+  ilock(ip);
   ip->nlink += 1;
   iupdate (ip);
 
-  dp = iget(rootdev, pinum);
   wdir(dp, name2, ip->inum);
   iput(dp);
   iput(ip);

fsvar.h

@@ -14,3 +14,7 @@ struct inode {
 };
 
 extern uint rootdev;
+
+#define NAMEI_LOOKUP 1
+#define NAMEI_CREATE 2
+#define NAMEI_DELETE 3

syscall.c

@@ -228,7 +228,7 @@ sys_open(void)
     return -1;
   if((l = checkstring(arg0)) < 0)
     return -1;
-  if((ip = namei(cp->mem + arg0, 0)) == 0) {
+  if((ip = namei(cp->mem + arg0, NAMEI_LOOKUP, 0)) == 0) {
     if (arg1 & O_CREATE) {
       if (l >= DIRSIZ)
 	return -1;
@@ -356,7 +356,7 @@ sys_exec(void)
     return -1;
   if(checkstring(arg0) < 0)
     return -1;
-  ip = namei(cp->mem + arg0, 0);
+  ip = namei(cp->mem + arg0, NAMEI_LOOKUP, 0);
   if(ip == 0)
     return -1;
 
@@ -494,7 +494,7 @@ sys_block(void)
           ip->type, ip->nlink, ip->size, ip->addrs[0]);
   iput(ip);
 
-  ip = namei(".././//./../usertests", 0);
+  ip = namei(".././//./../usertests", NAMEI_LOOKUP, 0);
   if(ip){
     cprintf("namei(usertests): %d %d %d %d %d %d %d %d\n",
             ip->dev, ip->inum, ip->count, ip->busy,

usertests.c

@@ -231,7 +231,7 @@ void
 createdelete()
 {
   int pid, i, fd;
-  int n = 10; // for now, fit in one directory block
+  int n = 20;
   char name[32];
 
   pid = fork();