Btrfs-progs: let btrfs-image actually work on a balanced fs

We use the read extent buffer infrastructure to read the super block when we are
creating a btrfs-image.  This works out fine most of the time except when the fs
has been balanced, then it fails to map the super block.  So we could fix
btrfs-image to read in the super in a special way, but thats more code.  So
instead just check in the eb reading code if we are reading the super and then
don't bother mapping the block, just read the actual offset.  This fixed some
poor guy who was trying to btrfs-image his fs that had been balanced.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.cz>

1 files changed, 2 insertions, 1 deletions

diff --git a/disk-io.c b/disk-io.c
index 26a532e4..34c0a972 100644
--- a/disk-io.c
+++ b/disk-io.c
@@ -201,7 +201,8 @@ int read_whole_eb(struct btrfs_fs_info *info, struct extent_buffer *eb, int mirr
 		read_len = bytes_left;
 		device = NULL;
 
-		if (!info->on_restoring) {
+		if (!info->on_restoring &&
+		    eb->start != BTRFS_SUPER_INFO_OFFSET) {
 			ret = btrfs_map_block(&info->mapping_tree, READ,
 					      eb->start + offset, &read_len, &multi,
 					      mirror, NULL);