generic, xfs: test scatter-gather atomic file updates

generic, xfs: test scatter-gather atomic file updates

Make sure that FILE_SWAP_RANGE_SKIP_FILE1_HOLES does what we want it to
do -- provide a means to implement scatter-gather atomic file writes.
That means we create a temporary file, write whatever sparse bits to it
that we want, and swap the non-hole parts of the temp file.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>