Re: [Qemu-devel] [PATCH v4 2/3] linux-aio: implement io plug, unplug and flush io queue

[Ming Lei]

On Thu, Jul 3, 2014 at 6:22 PM, Kevin Wolf <address@hidden> wrote:
> Am 03.07.2014 um 11:51 hat Ming Lei geschrieben:
>> Hi Kevin,
>>
>> On Thu, Jul 3, 2014 at 5:40 PM, Kevin Wolf <address@hidden> wrote:
>> > Am 02.07.2014 um 14:18 hat Ming Lei geschrieben:
>> >> This patch implements .bdrv_io_plug, .bdrv_io_unplug and
>> >> .bdrv_flush_io_queue callbacks for linux-aio Block Drivers,
>> >> so that submitting I/O as a batch can be supported on linux-aio.
>> >>
>> >> Signed-off-by: Ming Lei <address@hidden>
>> >
>> > Just a couple of minor comments, see inline.
>>
>> Thanks for your review.
>>
>> >> +void laio_io_plug(BlockDriverState *bs, void *aio_ctx)
>> >> +{
>> >> +    struct qemu_laio_state *s = aio_ctx;
>> >> +
>> >> +    s->io_q.plugged++;
>> >> +}
>> >> +
>> >> +int laio_io_unplug(BlockDriverState *bs, void *aio_ctx, bool unplug)
>> >> +{
>> >> +    struct qemu_laio_state *s = aio_ctx;
>> >> +    int ret = 0;
>> >> +
>> >
>> > How about an assert(s->io_q.plugged > 0); here?
>>
>> how about just adding a warning because flush io queue uses
>> the function too?
>
> Good point, this is what the assertion should look like then:
>
>     assert(s->io_q.plugged > 0 || !unplug);

OK, will do it.

>> Also that is why 'plugged' is defined as signed.
>
> I don't understand. The flush function leaves s->io_q.plugged alone
> (otherwise it would be buggy), so how can it ever become negative? And
> if you say that a negative value is valid, what would it even mean?

I mean it is easy to detect bug with negative value, :-)

Thanks,
--
Ming Lei