[libcamera-devel] use of v4l2-compat.so

[Laurent Pinchart]

Hi Nicolas,

On Fri, Jun 19, 2020 at 11:31:43AM -0400, Nicolas Dufresne wrote:
> Le mardi 16 juin 2020 à 23:38 +0530, naidu nama a écrit :
> > Hi team,
> > By default gstreamer is not using v4l2-compat.so.So,then what is the
> > use of v4l2 folder in libcamera.The goal is to by-pass the v4l2linux
> > API and use the libcamera API.So,what is the use of this v4l2 folder.
> 
> It is what is is, a work in progress LD_PRELOAD wrapper for "legacy"
> applications. Such a wrap would be achieve in a lauch script (or XDG desktop
> file). We suspect some app will take a long time to migrate, and would like to
> we able to use cameras on the IPU3 laptops and ARM devices before they are
> ported.
> 
> As for browser and sandboxed apps, it's all clear. In the flatpak community,
> they really want to stop giving /dev access to apps unless strictly needed,
> specially for V4L2 as it's then impossible to reclaim the access. But there is a
> WIP libcamera backend in pipewire already, so that is one way, but it does not
> really offer the features of libcamera. That all needs to be designed, I do
> expect mixed support in the upcoming future (some browser may us libcamera, some
> will do pipewire, as they will have to decide between sandboxing and features).

For pipewire-based stacks, we will need a camera backend for pipewire,
as well as a frontend API for applications. Provided we use libcamera as
a backend, do you think it would make sense to offer the same API for
the frontend ? It would require a libcamera API implementation on top of
pipewire, and would allow applications to use the same API, regardless
of whether pipewire is part of the camera stack or not.

> > On Tue, Jun 16, 2020 at 12:40 AM Nicolas Dufresne wrote:
> >> Le lundi 15 juin 2020 à 23:38 +0530, naidu nama a écrit :
> >>> Hi,
> >>> What does this wrapper library mean?
> >>> where can i find this API??
> >> 
> >> The API is V4L2 API, this library will catch calls to
> >> open/close/ioctl/poll and when they match a V4L2 use cases, they will
> >> be emulated on top of libcamera.
> >> 
> >>> 
> >>> On Mon, Jun 15, 2020 at 9:32 PM Nicolas Dufresne <nicolas at ndufresne.ca>
> >>> wrote:
> >>>> Le lundi 15 juin 2020 à 11:52 -0400, Nicolas Dufresne a écrit :
> >>>>> Le lundi 15 juin 2020 à 18:11 +0300, Laurent Pinchart a écrit :
> >>>>>> On Mon, Jun 15, 2020 at 11:06:45AM -0400, Nicolas Dufresne wrote:
> >>>>>>> Le lundi 15 juin 2020 à 18:52 +0530, naidu nama a écrit :
> >>>>>>>> Hi,
> >>>>>>>> I am able to build the v4l2 directory.I am getting a shared libary
> >>>>>>>> v4l2-compat.so.How can i use this in my libcamera or how can i test
> >>>>>>>> that v4l2-compat.so
> >>>>>>> 
> >>>>>>> One way is to make sure it's in your library path, and
> >>>>>>> use LD_PRELOAD=v4l2-compat.so .  Last time I tried it was missing
> >>>>>>> poll() emulation.
> >>>>>> 
> >>>>>> poll() support has been merged, along with several bug fixes. Paul is
> >>>>>> working on additional fixes, they should hopefully land this week.
> >>>>> 
> >>>>> Great ! I confirm it works under GStreamer now:
> >>>>> 
> >>>>> LD_LIBRARY_PATH=$(pwd)/build/src/v4l2 LD_PRELOAD=v4l2-compat.so gst-
> >>>>> launch-1.0 v4l2src ! glimagesink
> >>>> 
> >>>> Well, it *minimally* works. It seems that it's impossible to pick
> >>>> resolution different from 160x120, or select JPEG. As for other app,
> >>>> libv4l2 wrapper don't seem handled, in firefox it does not get used and
> >>>> it causes chrome to hang at start.

-- 
Regards,

Laurent Pinchart