libxfs: bmap btree owner swap support

libxfs: bmap btree owner swap support

For CRC enabled filesystems, we can't just swap inode forks from one
inode to another when defragmenting a file - the blocks in the inode
fork bmap btree contain pointers back to the owner inode. Hence if
we are to swap the inode forks we have to atomically modify every
block in the btree during the transaction.

This patch brings across the kernel code for doing the owner
swap of an entire fork - something that we are likely to end up
needing in xfs_repair when reparenting stray inodes to lost+found -
without all the associated swap extents transaction and recovery
cruft as those parts are not needed in userspace.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>