> Hi Hans,
>
> On Saturday 13 February 2010 15:42:20 Hans Verkuil wrote:
>> On Wednesday 10 February 2010 15:58:09 Sakari Ailus wrote:
>> > Add support for subscribing all events with a special id
>> V4L2_EVENT_ALL.
>> > If V4L2_EVENT_ALL is subscribed, no other events may be subscribed.
>> > Otherwise V4L2_EVENT_ALL is considered just as any other event.
>>
>> We should do this differently. I think that EVENT_ALL should not be used
>> internally (i.e. in the actual list of subscribed events), but just as a
>> special value for the subscribe and unsubscribe ioctls. So when used
>> with
>> unsubscribe you can just unsubscribe all subscribed events and when used
>> with subscribe, then you just subscribe all valid events (valid for that
>> device node).
>>
>> So in v4l2-event.c you will have a v4l2_event_unsubscribe_all() to
>> quickly
>> unsubscribe all events.
>>
>> In order to easily add all events from the driver it would help if the
>> v4l2_event_subscribe and v4l2_event_unsubscribe just take the event type
>> as argument rather than the whole v4l2_event_subscription struct.
>>
>> You will then get something like this in the driver:
>>
>> if (sub->type == V4L2_EVENT_ALL) {
>> int ret = v4l2_event_alloc(fh, 60);
>>
>> ret = ret ? ret : v4l2_event_subscribe(fh, V4L2_EVENT_EOS);
>> ret = ret ? ret : v4l2_event_subscribe(fh, V4L2_EVENT_VSYNC);
>> return ret;
>> }
>>
>> An alternative might be to add a v4l2_event_subscribe_all(fh, const u32
>> *events) where 'events' is a 0 terminated list of events that need to be
>> subscribed.
>
> Then don't call it v4l2_event_subscribe_all if it only subscribes to a set
> of
> event :-)
>
>> For each event this function would then call:
>>
>> fh->vdev->ioctl_ops->vidioc_subscribe_event(fh, sub);
>>
>> The nice thing about that is that in the driver you have a minimum of
>> fuss.
>>
>> I'm leaning towards this second solution due to the simple driver
>> implementation.
>>
>> Handling EVENT_ALL will simplify things substantially IMHO.
>
> I'm wondering if subscribing to all events should be allowed. Do we have
> use
> cases for that ? I'm always a bit cautious when adding APIs with no users,
> as
> that means the API has often not been properly tested against possible use
> cases and mistakes will need to be supported forever (or at least for a
> long
> time).
I think that is a good point. Supporting V4L2_EVENT_ALL makes sense for
unsubscribe, but does it makes sense for subscribe as well? I think it
does not. It just doesn't feel right when I tried to implement it in ivtv.
I also wonder whether the unsubscribe API shouldn't just receive the event
type instead of the big subscription struct. Or get its own struct. I
don't think it makes much sense that they both have the same struct.
Regards,
Hans
>
> --
> Regards,
>
> Laurent Pinchart
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--
Hans Verkuil - video4linux developer - sponsored by TANDBERG Telecom
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