This patch pulls back backref.c, adds a couple of helpers everywhere that it
needs, and cleans up backref.c to fit in btrfs-progs. Thanks,
Signed-off-by: Josef Bacik <jbacik@fb.com>
[removed free_some_buffers after "do not reclaim extent buffer"]
Signed-off-by: David Sterba <dsterba@suse.cz>
