xfs: implement swapext for rmap filesystems

Implement swapext for filesystems that have reverse mapping.  Back in
the reflink patches, we augmented the bmap code with a 'REMAP' flag
that updates only the bmbt and doesn't touch the allocator and
implemented log redo items for those two operations.  Now we can
rewrite extent swapping as a (looong) series of remap operations.

This is far less efficient than the fork swapping method implemented
in the past, so we only switch this on for rmap.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 75bf18b..2586c9c 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -3373,6 +3373,11 @@
 DEFINE_INODE_IREC_EVENT(xfs_reflink_cancel_cow);
 DEFINE_INODE_ERROR_EVENT(xfs_reflink_cancel_pending_cow_error);
 
+/* rmap swapext tracepoints */
+DEFINE_INODE_IREC_EVENT(xfs_swap_extent_rmap_remap);
+DEFINE_INODE_IREC_EVENT(xfs_swap_extent_rmap_remap_piece);
+DEFINE_INODE_ERROR_EVENT(xfs_swap_extent_rmap_error);
+
 #endif /* _TRACE_XFS_H */
 
 #undef TRACE_INCLUDE_PATH