vfs: make remap_file_range functions take and return bytes completed

Change the remap_file_range functions to take a number of bytes to
operate upon and return the number of bytes they operated on.  This is a
requirement for allowing fs implementations to return short clone/dedupe
results to the user, which will enable us to obey resource limits in a
graceful manner.

A subsequent patch will enable copy_file_range to signal to the
->clone_file_range implementation that it can handle a short length,
which will be returned in the function's return value.  For now the
short return is not implemented anywhere so the behavior won't change --
either copy_file_range manages to clone the entire range or it tries an
alternative.

Neither clone ioctl can take advantage of this, alas.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/ocfs2/refcounttree.h

@@ -119,7 +119,7 @@ int ocfs2_reflink_remap_range(struct file *file_in,
 			      loff_t pos_in,
 			      struct file *file_out,
 			      loff_t pos_out,
-			      u64 len,
+			      loff_t len,
 			      unsigned int remap_flags);
 
 #endif /* OCFS2_REFCOUNTTREE_H */