ABI stability for loadable modules

[Benjamin Kaduk]

On Wed, 28 Oct 2015, Koert van der Veer wrote:

> TL;DR: Can I safely load a kernel module compiled against a slightly
> different kernel?
>
>
> I maintain a fleet of FreeBSD machines. We've encountered a problem with
> one of the modules (iscsi doesn't allow passwords > 16 chars). I've
> determined that patching the module solves the problem for us, and doesn't
> affect any other kernel component. I'd like to distribute the patched
> module and user-space components. My use-case allows me to unload the iscsi
> module, but doesn't allow me to reboot the machine.
>
>
> However, we're running an array of different kernels (10.0-RELEASE,
> 10.0-RELEASE-p9, 10.0-STABLE, 10.1-RELEASE, 10.1-RELEASE-p6). I'd like to
> minimize the number of distinct binaries being distributed, so preferably
> I'd compile only one or two. My preliminary tests on VMs show me that this
> does not cause any immediate problems. Is this actually safe, or do I need
> to make distinct sets of binaries for each minor version and patchlevel of
> kernel in production?

Kernel ABI stability is guaranteed(*) within a major release branch.

-Ben

(*) there are occasional exceptions involving portions of the network
stack, but 10.x is probably better than 9.x in this regard