[PATCH v2] Btrfs: send, don't error in the presence of subvols/snapshots

[Filipe David Borba Manana <fdmanana@gmail.com>]

If we are doing an incremental send and the base snapshot has a
directory with name X that doesn't exist anymore in the second
snapshot and a new subvolume/snapshot exists in the second snapshot
that has the same name as the directory (name X), the incremental
send would fail with -ENOENT error. This is because it attempts
to lookup for an inode with a number matching the objectid of a
root, which doesn't exist.

Steps to reproduce:

    mkfs.btrfs -f /dev/sdd
    mount /dev/sdd /mnt

    mkdir /mnt/testdir
    btrfs subvolume snapshot -r /mnt /mnt/mysnap1

    rmdir /mnt/testdir
    btrfs subvolume create /mnt/testdir
    btrfs subvolume snapshot -r /mnt /mnt/mysnap2

    btrfs send -p /mnt/mysnap1 /mnt/mysnap2 -f /tmp/send.data

A test case for xfstests follows.

Reported-by: Robert White <rwhite@pobox.com>
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
---

V2: Simpler version.

 fs/btrfs/send.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 1a65a40..2722b26 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -1664,6 +1664,10 @@ static int lookup_dir_item_inode(struct btrfs_root *root,
 		goto out;
 	}
 	btrfs_dir_item_key_to_cpu(path->nodes[0], di, &key);
+	if (key.type == BTRFS_ROOT_ITEM_KEY) {
+		ret = -ENOENT;
+		goto out;
+	}
 	*found_inode = key.objectid;
 	*found_type = btrfs_dir_type(path->nodes[0], di);
 
-- 
1.9.1