[DRBD-user] Updating Kernel w/out Updating DRBD

[Roland Kammerer]

On Fri, Jun 22, 2018 at 08:43:32AM +0000, Eric Robinson wrote:
> > From: Veit Wahlich [mailto:cru.lists at zodia.de]
> > Sent: Friday, June 22, 2018 12:45 AM
> > To: Eric Robinson <eric.robinson at psmnv.com>
> > Cc: drbd-user at lists.linbit.com
> > Subject: Re: [DRBD-user] Updating Kernel w/out Updating DRBD
> > 
> > Hi Eric,
> > 
> > if your distro is el (e.g. RHEL/CentOS/Scientific), the kernel ABI
> > *should* not change during kernel updates, and copying modules from older
> > kernel versions as "weak updates" is not uncommon, following the slogan "old
> > module is better than no module". This is for example the case for CentOS 7
> > and worked quite well in the past, unfortunately with upgrade to 7.5 the ABI
> > changed nevertheless and caused many systems even to crash when using
> > some old modules, including drbd.
> > 
> > If you build the module on the system that runs it, you might consider
> > installing/building a dkms or akmod package of drbd instead, along with
> > dkms/akmod itself. When booting a new kernel, dkms/akmod will check
> > whether the packaged modules already exist for the running kernel, and if not,
> > they will be built and installed. This works as long as the module source builds
> > well against the kernel source/headers provided and all dependencies and build
> > tools are present.
> > 
> > Regards,
> > // Veit
> > 
> > Am Freitag, den 22.06.2018, 04:38 +0000 schrieb Eric Robinson:
> > > Greetings -
> > >
> > > We always build drbd as a KLM, and it seems that every time we update the
> > kernel (with yum update) we have to rebuild drbd. This is probably the worlds's
> > dumbest question, but is there a way to update the kernel without having to
> > rebuild drbd every time?
> > >
> > > --Eric
> > >
> 
> 
> Also, I find it odd that the option to build from source is only in
> the DRBD 8.3 User Guide and was left out of the 8.4 and 9.X User
> Guides. (I'm sure the reason is obvious to everyone else I just missed
> something.) 

As I maintain parts of the build system and the documentation framework
I can answer that (happened at least once here on the ML):

- If information is in the UG and is wrong, it is a bug.
- Documenting all possible build flavors for all distributions we
  support is too much maintenance work. Looking at the build system and
  the various hacks we need for outdated distributions (especially the
  rpm ones with different and broken macros), that would fill pages in
  the UG to *really* get it right. And I'm reluctant to accept patches
  for "the general case", it always outdates and needs maintenance for
  basically no gain. If you need (special kinds of) packages, you are a)
  clever enough to figure it out on your own, or b) you let somebody
  else figure that out for you. Thanks to Veith for his great summary,
  we as LINBIT obviously also provide all kinds of packages for various
  kinds of distributions for our customers.

Regards, rck