On Wed, Jun 6, 2018 at 7:51 PM Pavel Machek <pavel@xxxxxx> wrote:
>
> HI!
>
> > > > Thanks for coming up with this proposal. Please see my comments below.
> > > >
> > > > > Ok, can I get any comments on this one?
> > > > > v4l2_open_complex("/file/with/descriptor", 0) can be used to open
> > > > > whole pipeline at once, and work if it as if it was one device.
> > > >
> > > > I'm not convinced if we should really be piggy backing on libv4l, but
> > > > it's just a matter of where we put the code added by your patch, so
> > > > let's put that aside.
> > >
> > > There was some talk about this before, and libv4l2 is what we came
> > > with. Only libv4l2 is in position to propagate controls to right
> > > devices.
> > >
> > > > Who would be calling this function?
> > > >
> > > > The scenario that I could think of is:
> > > > - legacy app would call open(/dev/video?), which would be handled by
> > > > libv4l open hook (v4l2_open()?),
> > >
> > > I don't think that kind of legacy apps is in use any more. I'd prefer
> > > not to deal with them.
> >
> > In another thread ("[ANN v2] Complex Camera Workshop - Tokyo - Jun,
> > 19"), Mauro has mentioned a number of those:
> >
> > "open source ones (Camorama, Cheese, Xawtv, Firefox, Chromium, ...) and closed
> > source ones (Skype, Chrome, ...)"
>
> Thanks for thread pointer... I may be able to get in using hangouts.
>
> Anyway, there's big difference between open("/dev/video0") and
> v4l2_open("/dev/video0"). I don't care about the first one, but yes we
> should be able to support the second one eventually.
>
> And I don't think Mauro says apps like Camorama are of open() kind.
I don't think there is much difference between open() and v4l2_open(),
since the former can be changed to the latter using LD_PRELOAD.
If we simply add v4l2_open_complex() to libv4l, we would have to get
developers of the applications (regardless of whether they use open()
or v4l2_open()) to also support v4l2_open_complex(). For testing
purposes of kernel developers it would work indeed, but I wonder if it
goes anywhere beyond that.
If all we need is some code to be able to test kernel camera drivers,
I don't think there is any big problem in adding v4l2_open_complex()
to libv4l. However, we must either ensure that either:
a) it's not going to be widely used
OR
b) it is designed well enough to cover the complex cases I mentioned
and which are likely to represent most of the hardware in the wild.
Best regards,
Tomasz
