Thanks for the updated debdiff as requested, LGTM now. Some minor cleanup 0.12.3-1ubuntu1 -> 0.12.3-1ubuntu0.1
Further I think we should add DKMS rebuild with the Focal kernel as test-step explicitly (it will be done on install of the upgrade anyway, but to be formally correct) ** Description changed: Release: 20.04/Focal Fossa [SRU Justification] Impact: Starting with kernel version 5.4 the v4l2-core started to add sanity checking on drivers when querying capabilities. First drivers are not supposed to modify an initially set device_caps attribute. And second, the returned set of capabilities must be a superset of those in device_caps. The v4l2loopback module fails on both checks which results in repeated warnings (with additional stack trace) starting with: - WARNING: CPU: 2 PID: 7234 at drivers/media/v4l2-core/v4l2-ioctl.c:1064 v4l_querycap+0x8f/0xa0 [videodev] - WARNING: CPU: 2 PID: 7234 at drivers/media/v4l2-core/v4l2-ioctl.c:1069 v4l_querycap+0x8f/0xa0 [videodev] - Fix: The proposed fix adds compat code which stops modifying device_caps - after initial setup for kernel versions 5.4 and later. Also for those - versions the initial setup excludes V4L2_CAP_VIDEO_CAPTURE and - V4L2_CAP_VIDEO_OUTPUT as those capabilities might be optionally set when - calling v4l_querycap() to indicate readyness. + Fix: + The proposed fix adds compat code which stops modifying device_caps after initial setup for kernel versions 5.4 and later. Also for those versions the initial setup excludes V4L2_CAP_VIDEO_CAPTURE and V4L2_CAP_VIDEO_OUTPUT as those capabilities might be optionally set when calling v4l_querycap() to indicate readyness. - Testcase: Inserting the DKMS module the following way should start showing the above warnings: - sudo modprobe v4l2loopback exclusive_caps=1 - Once the fixed version is used, there should no longer be any warnings. + Testcase: + #1 + DKMS build the updated version (should be implicitly done on an + upgrade of v4l2loopback) + But one can try to rebuild explicitly and check if any warnings are + given. This would be extra useful if a pre 5.4 kernel could be used as + well (not officially part of focal, therefore optional) - Regression Potential: The change affects the internal device_caps - variable only. If that is unexpectedly used by anything external (the - kernel code should be assumed to expect the modified form) the loopback - device might become unusable for recording/playback. I have been using - the modified driver for a while now as v4l2sink in obs-studio and saw - now issues. + #2 + Inserting the DKMS module the following way should start showing the + above warnings: + $ sudo modprobe v4l2loopback exclusive_caps=1 + Once the fixed version is used, there should no longer be any warnings. + + Regression Potential: + The change affects the internal device_caps variable only. If that is unexpectedly used by anything external (the kernel code should be assumed to expect the modified form) the loopback device might become unusable for recording/playback. I have been using the modified driver for a while now as v4l2sink in obs-studio and saw now issues. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1899633 Title: Repeated kernel warnings/stacktraces with kernel 5.4 and newer To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/v4l2loopback/+bug/1899633/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
