Hans Verkuil wrote:
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I'm not keen on using pointers insides structures unless there is a very
good reason to do so. In practice it complicates the driver code
substantially due to all the kernel-to-userspace copies that need to be
done that are normally handled by video_ioctl2. In addition it requires
custom code in the compat-ioctl32 part as well.
VIDIOC_DQEVENT then.
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The size of the structure is now 96 bytes. I guess we could make that
around 128 to allow a bit more space for data without really affecting
performance.
With 'big unions' I didn't mean the memory size. I think 64 bytes (16
longs) is a decent size. I was talking about the union definition in the
videodev2.h header.
That was a badly placed comment, but I meant the memory size. I have
currently no opinion on whether to use union or not.
[clip]
That said, I think the initial implementation should be that the
subscribe
ioctl gets a struct with the event type and a few reserved fields so
that
in the future we can use one of the reserved fields as a configuration
parameter. So for now we just have some default watermark that is set by
the
driver.
I'd like to think a queue size defined by the driver is fine at this
point. It's probably depending on the driver rather than application how
long the queue should to be. At some point old events start becoming
uninteresting...
Question: will we drop old events or new events? Or make this
configurable? Or driver dependent?
This should the same than for video buffers. I guess it's undefined? I'd
let the driver decide at this point.
--
Sakari Ailus
sakari.ailus@xxxxxxxxxxxxxxxxxxxxxxxxxx
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