(lkml dropped)

On Thursday 19 March 2009, Jon Masters wrote:
> On Thu, 2009-03-19 at 21:13 +0100, maximilian attems wrote:
> > > That would mean that m-i-t has created a backwards incompatibility
> > > problem _with itself_ and that the problem actually is "installing
> > > a kernel, that was built on a system with new m-i-t, on a system
> > > with old m-i-t".
>
> Looks like the problem is actually that depmod was run under the newer
> version and then you tried to use the generated files with an older
> modprobe. I'm not sure that's actually an error - it was noted that the
> slight format change was unideal for such unlikely cases and in fact we
> won't do that again in the future. But if you were just moving forwards
> from one release to the next you would have been fine - you're talking
> lack of forward compatibility actually.

The use case here, which I suspect is not all that uncommon, is that I 
built a kernel from upstream source on a (Debian unstable) system with 
the new version of depmod and then installed that kernel on a (Debian 
stable) system that has an older version of modprobe [1].

The kernel Makefile of course does:
/sbin/depmod -ae -F System.map -b $(INSTALL_MOD_PATH) $(KERNELRELEASE)

Because the old modprobe does not understand the new relative (or rather 
rootless) paths, aggravated by the fact that initramfs-tools does not 
error out or display errors from modprobe (probably for good historic 
reasons), I suddenly had an initramfs that contained no modules and thus 
a system that failed to reboot with the new kernel.

It took me quite a lot of time to trace it back to the upgrade of 
module-init-tools.

Needless to say that this had always worked without any problems before.



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