[RFC] linux-stable: Allow out of tree modules to survive

[joebonrichie]

Summary

Allow linux module updates to survive moss state changes using the same trick as /usr/local

Test Plan

out of tree installed module framework-laptop-kmod now survives moss state changes

Checklist

• Recipe was built and tested against the volatile stream
• This change could gainfully be highlighted in the Stream Update notes once merged

[hphilm]

So this would partly enable dkms support as well? Since we already have some extramodules like Nvidia driver compiled per kernel update, do we see any issues adding this as well?

[joebonrichie]

It look's like our default make modules_install behavior installs to /lib/modules/<kernel-version>/updates but we install packaged out of tree modules e.g nvidia to /lib/modules/<kernel-version>/extra

Currently the user will still have to manually rebuild and install the module if the kernel is updated but could take a look at getting dkms working as well. All this change does for the moment is add an escape hatch for the updates module folder so it doesn't get wiped with each moss transaction.

[ReillyBrogan]

Wouldn't it make more sense to use depmod.d configuration instead?

[joebonrichie]

Yeah that's definitely an option, could add a default depmod conf e.g.

/etc/depmod.d/usermods.conf
external * /var/lib/kernel-modules

The user can override INSTALL_MOD_PATH to make modules_install to install to the var location and that should work

I think the tricky bit is documentation/getting this to work OOTB, you'd probably want make modules_install to just work instead of being a special snowflake distribution.

[hphilm]

If with this current change enables something without a fuzz why not merge it as is ...

[joebonrichie]

There's an issue where stale directory entries remain in /var once the kernel has been updated, hold off for now.

[ReillyBrogan]

I think the tricky bit is documentation/getting this to work OOTB

My strong preference is adding documentation for this instead.