[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>

1 files changed, 18 insertions, 2 deletions

diff --git a/fs/namei.c b/fs/namei.c
index a7f7f44119b3..fa8df81ce8ca 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1577,19 +1577,35 @@ do_link:
  *
  * 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;