Bug#779616: debian-cd: broken debian-testing-$arch-netinst.iso generation?
On Thu, 2015-03-05 at 12:25 +0100, Cyril Brulebois wrote:
> > OK. Assuming amd64 is working OK, I should check the rsync has not
> > broken - that seems to be the most likely cause right now. Thinking:
> > it would also be lovely to verify the versions of vmlinuz and the
> > kernel udebs in debian-cd at build time, and (optionally?) abort the
> > build if we know we're going to be making broken images. What do you
> > think?
>
> There's no way for us to know a breakage is going to happen. In this
> particular case the ABI is the same, say 3.16.0-4-amd64; the ABI is
> embedded in kernel udeb package names, so if the ABI matches, udebs are
> supposed to be compatible with the kernel. I'm not sure why that is not
> the case here (maybe the ABI doesn't cover or not completely udebs?). We
> really shouldn't enforce using the very same revision for kernel and
> module udebs, IMHO.
Caveat: I might be talking out my a**e here...
I think the ABI only guarantees you can load old modules into a newer
vmlinuz. In particular I think it doesn't guarantee that you can load
newer modules into an older vmlinuz (even if the ABI is the same).
The ABI is there to stop your existing modules from breaking when you
update the kernel.
IOW it is permissible for a module to gain a dependency on a new symbol
provided by a newer vmlinuz.
This is why local netboot pxe infra sometimes breaks -- they have a
vmlinuz downloaded locally but are pulling udebs off the network, which
might therefore be newer.
Please reread my caveat now though ;-)
Ian.
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