generic: check direct IO writes with io_uring and O_DSYNC are durable

generic: check direct IO writes with io_uring and O_DSYNC are durable

Test that direct IO writes with io_uring and O_DSYNC are durable if a
power failure happens after they complete.

This is motivated by a regression on btrfs, affecting 5.15 stable
kernels and kernels up to 6.0, where often the writes were not
persisted (same behaviour as if O_DSYNC was not provided). This was
recently fixed by the following commit:

8184620ae212 ("btrfs: fix lost file sync on direct IO write with
nowait and dsync iocb")

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>