batman-adv-legacy build fails sometimes

[oliver]

When installing a kernel upgrade, our (customized) build trigger for the batman-adv-legacy module (in old version 2013.4.0) sometimes fails. As result, after rebooting the new kernel loads the system-provided module (version 2018.3) which is not compatible with our current network setup.

It looks like this problem occurs when the "linux-image" package is upgraded before the "linux-headers" package is upgraded. If the upgrade is done by the "unattended-upgrade" tool, this can happen. This problem can be seen in /var/log/apt/term.log.

The build of our own old batman-adv-legacy module is triggered by the /etc/kernel/postinst.d/00dkms-batman-adv-downgrade script.

So maybe a solution could be to add a symlink to that 00dkms-batman-adv-downgrade scriptinto /etc/kernel/header_postinst.d/ .

Side note: once the problem occurs, it can be fixed with these commands:

• dkms uninstall -m batman-adv-legacy -v 2013.4.0 -k $(uname -r) -a x86_64
• dkms install --force -m batman-adv-legacy -v 2013.4.0 -k $(uname -r) -a x86_64
• reboot
• after reboot, batctl -v should show that some "batman-adv: 2013.4 ..." version is in use.