Hi Moritz, On 15/02/2019 08:45, Moritz Dötterl wrote: > Hello > > Recently we updated the Kernel on our Ubuntu machines from 4.15 to 4.18 > because the OS was randomly freezing. However with the new Kernel we ran > into a problem regarding our two webcams. We had two /dev/video device > files per camera of which only one seemed to work. Yes, a new device node has been added to represent the meta-data from the device. You should be able to enumerate the devices, and you should verify/validate the capabilities of the device after you open it. A UVC capture device will expose the V4L2_CAP_VIDEO_OUTPUT capability flag. > The problem was that > our application would just randomly open one of those two device files Is this an application you have control over the source code for? or some external application? > and then crashed if it opened the wrong one. After some search i figured > out that the second device file is for meta data (which might not be > provided by our camera i guess...). However i also found the line in the > uvc_driver.c which generates the device file > (https://elixir.bootlin.com/linux/v4.18/source/drivers/media/usb/uvc/uvc_driver.c#L2005) > that line including the whole uvc_metadata.c was added when comparing > 4.15 and 4.18 Kernel. I took that line out, recompiled the Kernel and > ended up with having only one /dev/video device file per camera. I also > found it is using the exact same function to register the device node > that the uvc_driver.c is using and also using the same vfl_devnode_type > (VFL_TYPE_GRABBER) and therefore ending up as a /dev/video device. Was > that move on purpose? Yes, this addition was on purpose. It was added by the following patch: https://www.spinics.net/lists/linux-media/msg125681.html I've added the linux-media mailing list on Cc where you will be able to find better support if this topic causes further problems. > Why was it split up in two device files, or is > that just added functionality? I believe it is just added functionality - not split. > I would rather like this device file to > have a different name because in this setup it is not easily decidable Perhaps some different naming might have continued to hide this issue for you but it would only have hidden a potential bug. Even with a different name, you can not expect that all /dev/video* nodes are capture devices. They can be output devices or M2M devices for example. Your application should always check the device capabilities using the V4L2 API's as applicable. > if a /dev/video device is the "real" webcam or just the meta data... So > i would prefer that to end up as something like /dev/metavideo or so ( > or maybe easier: change the type to VFL_TYPE_SUBDEV so it will end up as > a v4l-subdev device, that sounds more suitable for me...) I think in this instance it has to be a full video node and not a subdev so that data can be captured from the device node. > What are the plans for this in future kernel versions? Should it stay > like it is now or are there plans to change/evolve the meta data > handling again? This is in mainline now - so I would expect it to continue to be supported. > > > Thanks very much. > > > Best regards / Mit freundlichen Grüßen > *Moritz Dötterl* > > Pentland Firth Software GmbH > > Hofmannstr. 61 > 81379 München, Germany > > Mobile: +49 17655389056 > > moritz.doetterl@xxxxxxxxxxxxxxxxx <mailto:aron.borbath@xxxxxxxxxxxxxxxxx> > > ---------------------------------------------------------------------------------------------------------------------------------- > Pentland Firth is *Microsoft Gold Partner* > > Brands we own: www.whiz-cart.com <http://www.whiz-cart.com/> > ---------------------------------------------------------------------------------------------------------------------------------- > Sitz der Gesellschaft: München, Handelsregister München, HRB 155 786, > Geschäftsführer: Frank Heinrich > > > > > _______________________________________________ > Linux-uvc-devel mailing list > Linux-uvc-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.sourceforge.net/lists/listinfo/linux-uvc-devel > -- Regards -- Kieran
