The actor should never return a larger value than the length that was
passed in.  The current code handles this gracefully, but the opcoming
iter model will be more picky.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <djwong@kernel.org>
Signed-off-by: NDarrick J. Wong <djwong@kernel.org>