btrfs: test direct IO write against raid5/6 filesystems

Test that a direct IO write works against raid5/6 filesystems and that
after the write operation we are able to read back the correct data
and scrub operations don't find any errors.

This test is motivated by a regression introduced in the merge window
for the 4.13 linux kernel, which was undetected by the current set of
test cases. The issue is fixed by the following patch:

  "Btrfs: fix write corruption due to bio cloning on raid5/6"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
3 files changed