[DRBD-user] Do You Always Have to Upgrade/Rebuild DRBD Whenever You Upgrade the Kernel?

[Roland Kammerer]

On Mon, Apr 18, 2022 at 09:43:38PM +0000, Eric Robinson wrote:
> New kernel versions are released fairly often. What are the rules
> about upgrading DRBD when that happens? Is it always necessary, or are
> there certain thresholds within which it is okay to upgrade the kernel
> without rebuilding DRBD? Rebuilding DRBD every time is pretty
> disruptive.

"depends", but in general that is how things work, there are no stable
kABI guarantees from the Linux kernel itself. So you have to rebuild
external modules. This is for example why dkms exists.

In more detail it depends on the distribution. RHEL guarantees a stable
kABI for certain symbols. Unfortunately sometimes even they make
mistakes and break it, but one usually gets away with relatively few
builds. Debian tries to keep a stable kABI, Ubuntu does not seem to do
so.

Needless to say that we for example test for new RHEL kernels and compat
and provide new binary modules for our customers. They just upgrade and
don't have to worry. Same for Debian - we build when we need to - we
build every Ubuntu kernel release. For the other distros it depends on
their model (which roughly depends on how "good" their RHEL clone
actually is). Even with rotating out old kernels rather quickly, we get
3 figure kernel numbers we build for easily.

Regards, rck