Merge branch 'work.lookup' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull more ->lookup() cleanups from Al Viro:
 "Some ->lookup() instances are still overcomplicating the life
  for themselves, open-coding the stuff that would be handled by
  d_splice_alias() just fine.

  Simplify a couple of such cases caught this cycle and document
  d_splice_alias() intended use"

* 'work.lookup' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  Document d_splice_alias() calling conventions for ->lookup() users.
  simplify btrfs_lookup()
  clean erofs_lookup()

Documentation/filesystems/porting

@@ -622,3 +622,14 @@ in your dentry operations instead.
 	alloc_file_clone(file, flags, ops) does not affect any caller's references.
 	On success you get a new struct file sharing the mount/dentry with the
 	original, on failure - ERR_PTR().
+--
+[recommended]
+	->lookup() instances doing an equivalent of
+		if (IS_ERR(inode))
+			return ERR_CAST(inode);
+		return d_splice_alias(inode, dentry);
+	don't need to bother with the check - d_splice_alias() will do the
+	right thing when given ERR_PTR(...) as inode.  Moreover, passing NULL
+	inode to d_splice_alias() will also do the right thing (equivalent of
+	d_add(dentry, NULL); return NULL;), so that kind of special cases
+	also doesn't need a separate treatment.

drivers/staging/erofs/namei.c

@@ -223,18 +223,13 @@ static struct dentry *erofs_lookup(struct inode *dir,
 	if (err == -ENOENT) {
 		/* negative dentry */
 		inode = NULL;
-		goto negative_out;
-	} else if (unlikely(err))
-		return ERR_PTR(err);
-
-	debugln("%s, %s (nid %llu) found, d_type %u", __func__,
-		dentry->d_name.name, nid, d_type);
-
-	inode = erofs_iget(dir->i_sb, nid, d_type == EROFS_FT_DIR);
-	if (IS_ERR(inode))
-		return ERR_CAST(inode);
-
-negative_out:
+	} else if (unlikely(err)) {
+		inode = ERR_PTR(err);
+	} else {
+		debugln("%s, %s (nid %llu) found, d_type %u", __func__,
+			dentry->d_name.name, nid, d_type);
+		inode = erofs_iget(dir->i_sb, nid, d_type == EROFS_FT_DIR);
+	}
 	return d_splice_alias(inode, dentry);
 }
 

fs/btrfs/inode.c

@@ -5764,16 +5764,10 @@ static int btrfs_dentry_delete(const struct dentry *dentry)
 static struct dentry *btrfs_lookup(struct inode *dir, struct dentry *dentry,
 				   unsigned int flags)
 {
-	struct inode *inode;
-
-	inode = btrfs_lookup_dentry(dir, dentry);
-	if (IS_ERR(inode)) {
-		if (PTR_ERR(inode) == -ENOENT)
-			inode = NULL;
-		else
-			return ERR_CAST(inode);
-	}
+	struct inode *inode = btrfs_lookup_dentry(dir, dentry);
 
+	if (inode == ERR_PTR(-ENOENT))
+		inode = NULL;
 	return d_splice_alias(inode, dentry);
 }