xfs: reflink extents from one file to another

Reflink extents from one file to another; that is to say, iteratively
remove the mappings from the destination file, copy the mappings from
the source file to the destination file, and increment the reference
count of all the blocks that got remapped.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_reflink.h

@@ -43,5 +43,7 @@ extern int xfs_reflink_cancel_cow_range(struct xfs_inode *ip, xfs_off_t offset,
 extern int xfs_reflink_end_cow(struct xfs_inode *ip, xfs_off_t offset,
 		xfs_off_t count);
 extern int xfs_reflink_recover_cow(struct xfs_mount *mp);
+extern int xfs_reflink_remap_range(struct xfs_inode *src, xfs_off_t srcoff,
+		struct xfs_inode *dest, xfs_off_t destoff, xfs_off_t len);
 
 #endif /* __XFS_REFLINK_H */