Quoting Laurent Pinchart (2023-01-02 13:35:33) > Hello, > > On Mon, Jan 02, 2023 at 01:14:15PM +0000, Sakari Ailus wrote: > > On Wed, Dec 28, 2022 at 01:44:38AM +0000, Barnabás Pőcze wrote: > > > On 2022. december 26., hétfő 10:52, Laurent Pinchart wrote: > > > > 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@xxxxxxxxxxxxxxxx > > > > > --- > > > > > > > > > > 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. > > > > A sysfs attribute is not a great way to address this. > > > > libcamera certainly has information on whether streaming is ongoing. The > > information should come from there. Or Pipewire. Dbus perhaps? > > I tend to agree, I think this is best solved in userspace where PipeWire > can have a centralized view of all cameras in the system, and of their > users. I fear that misses the entire point I was trying to make. Lets say pipewire 'is' available and in use and can be used to capture video streams for video calls, that's fine. But what happens if a user runs a gstreamer pipeline without using the pipewire source, or a suspcious process runs "yavta" and captures an image or stream discreetly... Only the kernel has a true centralised view of what devices are in use. > > Alternatively libcamera could close the video devices while not streaming > > but that would involve e.g. releasing possible video buffer allocations as > > well, increasing streaming start latency. Or is it just that in that case 'lsof' should be sufficient? The problem I have with that is - just like with the issue when the Privacy LED comes on during power up/probe - then any time a device is opened to identify the device and not necessarily use it - the 'camera in use' notification would get flashed... > Closing video (and subdev) nodes when the camera is not in use would be > good I think. It doesn't mean we have to open them when starting > capture, explicit open/close operation (or similar, maybe introducing a > capture session object in the libcamera API would also make sense, it > should be considered as part of the same issue) could help with this. I'm not talking about libcamera in this thread. It's how does a user correctly identify when a camera is in use globally in a system. -- Kieran
