Oliver Neukum wrote:
>
> > Rather make this per open than per device. As is, it will really hurt
> > performance with multiple capturing opens (or doesn't v4l1 allow
> > this?). Can't the driver implement it's own semaphore if it needs it?
>
> Multiple opens are impossible under v4l.
> However multithreaded tasks could do concurrent reads or writes.
> This is not intended I think, thus the semaphores.
> It's hard to see how the hardware could do several reads at the same time.
> Thus v4l can do this for the drivers. This is a race that hits 2/3 of the usb
> video devices.
>
> Regards
> Oliver
I can see the problem, but I personally think that this should be
handled by the driver itself. If the driver can handle simultaneous
(for example, separate even/odd fileds) reads, let it, otherwise let it
serialise the operations itself.
As usual, this is just IMHO, but I think the idea of videodev.c was to
be a pretty lightweight wrapper, with the driver doing all the real
work.
-justin
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