Re: [PATCH v4 08/10] iotests.py: add verify_o_direct helper

[Nir Soffer]

On Thu, Aug 20, 2020 at 9:49 PM Vladimir Sementsov-Ogievskiy
<vsementsov@virtuozzo.com> wrote:
>
> Add python notrun-helper similar to _check_o_direct for bash tests.
> To be used in the following commit.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  tests/qemu-iotests/iotests.py | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
> index 717b5b652c..369e9918b4 100644
> --- a/tests/qemu-iotests/iotests.py
> +++ b/tests/qemu-iotests/iotests.py
> @@ -1083,6 +1083,12 @@ def _verify_aio_mode(supported_aio_modes: 
> Sequence[str] = ()) -> None:
>      if supported_aio_modes and (aiomode not in supported_aio_modes):
>          notrun('not suitable for this aio mode: %s' % aiomode)
>
> +def verify_o_direct() -> None:
> +    with FilePath('test_o_direct') as f:
> +        qemu_img_create('-f', 'raw', f, '1M')
> +        if 'O_DIRECT' in qemu_io('-f', 'raw', '-t', 'none', '-c', 'quit', f):
> +            notrun(f'file system at {test_dir} does not support O_DIRECT')

Why not:

    with FilePath('test_o_direct') as f:
        try:
            fd = os.open(f, os.O_DIRECT | os.O_CREAT | os.O_RDWR)
        except OSError as e:
            if e.errno != errno.EINVAL:
                raise
            notrun(...)
        else:
           os.close(fd)

More verbose, but the intent is more clear, and we do not depend on the output
of qemu-io which is not a public API. For example if someone improves qemu-io
to fail with:

    Direct I/O is not supported

It would break the tests using this helper.

Nir

> +
>  def supports_quorum():
>      return 'quorum' in qemu_img_pipe('--help')
>
> --
> 2.21.3
>
>