[PATCH] add some comments to lookup_create()

In a duplicate of lookup_create in the af_unix code Al commented what's going on nicely, so let's bring that over to lookup_create before the copy is going away (I'll send a patch soon) Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>

[PATCH] add some comments to lookup_create()
In a duplicate of lookup_create in the af_unix code Al commented what's going on nicely, so let's bring that over to lookup_create before the copy is going away (I'll send a patch soon) Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Christoph Hellwig · Linus Torvalds
1 parent 70f09f1fdf
Showing 1 changed file with 18 additions and 2 deletions Side-by-side Diff
fs/namei.c
@@ -1577,19 +1577,35 @@
  *
  * Simple function to lookup and return a dentry and create it
  * if it doesn't exist.  Is SMP-safe.
+ *
+ * Returns with nd->dentry->d_inode->i_sem locked.
  */
 struct dentry *lookup_create(struct nameidata *nd, int is_dir)
 {
-	struct dentry *dentry;
+	struct dentry *dentry = ERR_PTR(-EEXIST);
  
 	down(&nd->dentry->d_inode->i_sem);
-	dentry = ERR_PTR(-EEXIST);
+	/*
+	 * Yucky last component or no last component at all?
+	 * (foo/., foo/.., /////)
+	 */
 	if (nd->last_type != LAST_NORM)
 		goto fail;
 	nd->flags &= ~LOOKUP_PARENT;
+
+	/*
+	 * Do the final lookup.
+	 */
 	dentry = lookup_hash(&nd->last, nd->dentry);
 	if (IS_ERR(dentry))
 		goto fail;
+
+	/*
+	 * Special case - lookup gave negative, but... we had foo/bar/
+	 * From the vfs_mknod() POV we just have a negative dentry -
+	 * all is fine. Let's be bastards - you had / on the end, you've
+	 * been asking for (non-existent) directory. -ENOENT for you.
+	 */
 	if (!is_dir && nd->last.name[nd->last.len] && !dentry->d_inode)
 		goto enoent;
 	return dentry;
...	...	@@ -1577,19 +1577,35 @@
1577	1577	*
1578	1578	* Simple function to lookup and return a dentry and create it
1579	1579	* if it doesn't exist. Is SMP-safe.
	1580	+ *
	1581	+ * Returns with nd->dentry->d_inode->i_sem locked.
1580	1582	*/
1581	1583	struct dentry lookup_create(struct nameidata nd, int is_dir)
1582	1584	{
1583		- struct dentry *dentry;
	1585	+ struct dentry *dentry = ERR_PTR(-EEXIST);
1584	1586
1585	1587	down(&nd->dentry->d_inode->i_sem);
1586		- dentry = ERR_PTR(-EEXIST);
	1588	+ /*
	1589	+ * Yucky last component or no last component at all?
	1590	+ * (foo/., foo/.., /////)
	1591	+ */
1587	1592	if (nd->last_type != LAST_NORM)
1588	1593	goto fail;
1589	1594	nd->flags &= ~LOOKUP_PARENT;
	1595	+
	1596	+ /*
	1597	+ * Do the final lookup.
	1598	+ */
1590	1599	dentry = lookup_hash(&nd->last, nd->dentry);
1591	1600	if (IS_ERR(dentry))
1592	1601	goto fail;
	1602	+
	1603	+ /*
	1604	+ * Special case - lookup gave negative, but... we had foo/bar/
	1605	+ * From the vfs_mknod() POV we just have a negative dentry -
	1606	+ * all is fine. Let's be bastards - you had / on the end, you've
	1607	+ * been asking for (non-existent) directory. -ENOENT for you.
	1608	+ */
1593	1609	if (!is_dir && nd->last.name[nd->last.len] && !dentry->d_inode)
1594	1610	goto enoent;
1595	1611	return dentry;