v4l2loopback-dkms from mantic is not compatible with kernel from lunar and fails when upgrading from lunar to mantic

[Thomas Debesse]

When upgrading from lunar to mantic I got this error:

```
Loading new v4l2loopback-0.12.7 DKMS files...
Building for 6.2.0-33-generic 6.5.0-9-generic
Building initial module for 6.2.0-33-generic
ERROR (dkms apport): kernel package linux-headers-6.2.0-33-generic is not supported
Error! Bad return status for module build on kernel: 6.2.0-33-generic (x86_64)
Consult /var/lib/dkms/v4l2loopback/0.12.7/build/make.log for more information.
dpkg: error processing package v4l2loopback-dkms (--configure):
 installed v4l2loopback-dkms package post-installation script subprocess returned error exit status 10
Processing triggers for man-db (2.11.2-3) ...
Errors were encountered while processing:
 v4l2loopback-dkms
```

It looks like v4l2loopback-dkms from mantic is not compatible with lunar kernel, but since I'm upgrading from lunar to mantic I'm still running the lunar kernel.

I was able to finish the mantic installation by doing:

```
apt-get remove v4l2loopback-dkms
apt-get --fix-broken install
```

I'll have to manually reinstall v4l2loopback-dkms after the reboot.

ProblemType: Bug
DistroRelease: Ubuntu 23.10
Package: v4l2loopback-dkms (not installed)
ProcVersionSignature: Ubuntu 6.2.0-33.33-generic 6.2.16
Uname: Linux 6.2.0-33-generic x86_64
NonfreeKernelModules: vboxnetadp vboxnetflt vboxdrv amddrm_ttm_helper amdttm amdxcp amddrm_buddy amd_sched amdkcl
ApportVersion: 2.27.0-0ubuntu5
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: GNOME
Date: Fri Oct 13 16:04:02 2023
RebootRequiredPkgs: Error: path contained symlinks.
SourcePackage: v4l2loopback
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.default.apport: [modified]
mtime.conffile..etc.default.apport: 2018-06-16T17:39:00.798346

[Steve Langasek (vorlon)]

Preferred outcome here is to fix the package that breaks across upgrades (v4l2loopback), not adding a quirk in ubuntu-release-upgrader. I don't think there is an existing "upgrade this before this" quirk type in u-r-u and even if there is, that is better expressed by package Breaks/Depends directly in the archive.

[Steve Langasek (vorlon)]

Oh, also

> Loading new v4l2loopback-0.12.7 DKMS files...
> Building for 6.2.0-33-generic 6.5.0-9-generic
> Building initial module for 6.2.0-33-generic

It's trying to rebuild for the kernel from the old release. That is NOT fixable from u-r-u, we ABSOLUTELY DO NOT remove the kernel from the old release from disk as part of the upgrade as it needs to be available as the fallback in case of any issues with the new kernel.

[Thomas Debesse (illwieckz)]

Maybe not building the new module with the old kernel is enough? One problem is that DKMS also builds for the current kernel (which is necessarily the one from the old release at the time of the upgrade).

But a perfect fix would be that the DKMS module would be compatible with both the new kernel from new Ubuntu release and the old kernel from old Ubuntu release.

The bug 2039283 is very similar, with virtualbox-dkms reproducing the same issue, maybe other DKMS packages are affected by the same problem.