Re: [RFC, libv4l]: Make libv4l2 usable on devices with complex pipeline

[Mauro Carvalho Chehab <mchehab+samsung@kernel.org>]

Em Wed, 6 Jun 2018 12:51:16 +0200
Pavel Machek <pavel@ucw.cz> escreveu:

> > > > 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.

All open source apps we care use v4l2_open() & friends. the ones
that use just open() work via LD_PRELOAD. It is a hack, but it
was needed when libv4l was added (as there were lots of apps
to be touched). Also, we had problems on that time with closed
source app developers. I guess nowadays, among v4l-specific
apps, only closed source ones use just open().

Haven't check how browsers open cameras, though. A quick look at the
Fedora 60 dependencies, though, doesn't show libv4l:

	https://rpmfind.net/linux/RPM/fedora/devel/rawhide/x86_64/f/firefox-60.0.1-5.fc29.x86_64.html

It might be statically linking libv4l, or maybe they rely on something
else (like java/flash/...), but I guess it is more likely that they're
just using open() somehow. The same kind of issue may also be present
on other browsers and on java libraries.

Thanks,
Mauro