Re: [RFC PATCH] media: v4l2-dev: sysfs: Support streaming attribute

Barnabás Pőcze
2022-12-28T01:44:55Z

Hi

On 2022. december 26., hétfő 10:52, Laurent Pinchart wrote:

> Hi Kieran,
>
> Thank you for the patch.
>
> On Fri, Dec 23, 2022 at 11:17:35PM +0000, Kieran Bingham wrote:
>
> > Provide a streaming attribute to allow userspace to interogate if a device
> > is actively streaming or not.
> >
> > This will allow desktop notifications to report if a camera or device
> > is active on the system, rather than just 'open' which can occur when
> > configuring the device.
> >
> > Bug: https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/2669
> > Signed-off-by: Kieran Bingham kieran.bingham@ideasonboard.com
> > ---
> >
> > This is a quick POC to see if such a facility makes sense.
> > I'm weary that not all video devices may have the queues registered on
> > the struct video_device, but this seems like an effective way to be able
> > to determine if a device is actively streaming on a system.
>
>
> I can imagine multiple problems, from race conditions to permissions and
> privacy. In order to comment on the fitness of this solution to address
> the problem you're trying to solve, could you describe the actual
> problem ?

The issue is explained in the following thread:
https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/2669#note_1697388

In short, the user wants to show a "camera-in-use" indicator when the laptop camera
is used. The script that the user previously had only checked if /dev/video0
was open in any process, if it was, the indicator was shown. However, libcamera
- at least at the moment - keeps the file descriptor open as long as the Camera
object exists, which pipewire keeps alive for the entire lifetime of the device,
therefore the "camera-in-use" indicator is always shown.

> [...]

Regards,
Barnabás Pőcze