fstests: add helper _require_xfs_io_shutdown

Requirements for tests that shutdown fs using "xfs_io -c shutdown".
The requirements are stricter than the requirement for tests that
shutdown fs using _scratch_shutdown helper.

Generally, with overlay fs, tests can do _scratch_shutdown, but not
xfs_io -c shutdown.

Encode this stricter requirement in helper _require_xfs_io_shutdown
and use it in test generic/623, to express that it cannot run on
overalyfs.

Reported-by: André Almeida <andrealmeid@igalia.com>
Link: https://lore.kernel.org/linux-fsdevel/20250521-ovl_ro-v1-1-2350b1493d94@igalia.com/
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Tested-by: André Almeida <andrealmeid@igalia.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>
2 files changed