[Bug 1905613] Re: Please backport v4l2loopback 0.12.5-1 (universe) from hirsute

[You-Sheng Yang]

** Description changed:

+ [SRU Justification]
+ 
+ [Impact]
+ 
+ On a MIPI camera through Intel IPU6 platform that its raw V4L2 loopback
+ interface is preserved for Intel Camera HAL libraries, a relay daemon +
+ v4l2loopback is used to allow the usage of legacy V4L2 based apps.
+ 
+ By design, the relayd will open v4l2sink to v4l2loopback OUTPUT deivce,
+ and it will only open libcamhal based GStreamer source element, and
+ therefore underlying camera hardware, until received new client
+ notifications via V4L2 Event API that is introduced in this SRU.
+ 
+ Besides, frame sizes/intervals enumeration is also fixed to meet better
+ compliance with user apps.
+ 
+ [Test Plan]
+ 
+ v4l2loopback doesn't support V4L2 Event API until recently, so requests
+ for the usage will always fail:
+ 
+   struct v4l2_event_subscription sub;
+   int fd;
+ 
+   memset (&sub, 0, sizeof (sub));
+   sub.type = ...;
+   if (ioctl (fd, VIDIOC_SUBSCRIBE_EVENT, &sub) == 0) // fail
+ 
+ With this fix, it shall support Event API operations, e.g.
+ VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT, VIDIOC_DQEVENT.
+ 
+ [Where problems could occur]
+ 
+ While a custom type of V4L2 event is now registered for OEM projects,
+ software expected same ID (numerically equivalent to
+ V4L2_EVENT_PRIVATE_START) may get confused. While this falls in the
+ private usage section, it's not supposed to be used in general, and when
+ it does, it should be under some presumptions, e.g. selected hardware,
+ so it's unlikely to happen on OEM projects.
+ 
+ For generic Ubuntu, programs may begin to take advantage of this new
+ capability to update its UI, or to take other actions after receiving
+ desired events. There might be behavior changes, but should be under the
+ original design if was done carefully.
+ 
+ [Other Info]
+ 
+ For Focal backports, 0.12.5-1 is equivalent to 0.12.3-1ubuntu0.3 plus
+ micro version updates, so there should be little risk backport a new
+ release, and we can drop additional patches carried. This implies bug
+ 1905613.
+ 
+ ========= original bug report ==========
+ 
  Please backport v4l2loopback 0.12.5-1 (universe) from hirsute to focal,
  groovy.
  
  Reason for the backport:
  ========================
  Makes dkms module compatible with 5.8 kernels eg linux-generic-hwe-20.04-edge
  
  Testing:
  ========
  Mark off items in the checklist [X] as you test them, but please leave the checklist so that backporters can quickly evaluate the state of testing.
  
  You can test-build the backport in your PPA with backportpackage:
  $ backportpackage -u ppa:<lp username>/<ppa name> -s hirsute -d focal v4l2loopback
  $ backportpackage -u ppa:<lp username>/<ppa name> -s hirsute -d groovy v4l2loopback
  
  * focal:
  [x] Package builds without modification
  [x] v4l2loopback-source installs cleanly and runs
  [x] v4l2loopback-dkms installs cleanly and runs
  [x] v4l2loopback-utils installs cleanly and runs
  * groovy:
  [x] Package builds without modification
  [x] v4l2loopback-source installs cleanly and runs
  [x] v4l2loopback-dkms installs cleanly and runs
  [x] v4l2loopback-utils installs cleanly and runs
  
  Reverse dependencies:
  =====================
  The following reverse-dependencies need to be tested against the new version of v4l2loopback. For reverse-build-dependencies (-Indep), please test that the package still builds against the new v4l2loopback. For reverse-dependencies, please test that the version of the package currently in the release still works with the new v4l2loopback installed. Reverse- Recommends, Suggests, and Enhances don't need to be tested, and are listed for completeness-sake.
  
  v4l2loopback-source
  -------------------
  
  v4l2loopback-dkms
  -----------------
  * gem-plugin-v4l2
-   [ ] focal (Reverse-Suggests)
-   [ ] groovy (Reverse-Suggests)
+   [ ] focal (Reverse-Suggests)
+   [ ] groovy (Reverse-Suggests)
  * xpra
-   [ ] focal (Reverse-Suggests)
-   [ ] groovy (Reverse-Suggests)
+   [ ] focal (Reverse-Suggests)
+   [ ] groovy (Reverse-Suggests)
  
  v4l2loopback-utils
  ------------------

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Title:
  Please backport v4l2loopback 0.12.5-1 (universe) from hirsute

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