Re: [Xen-devel] [PATCH 00/04] Kexec / Kdump: Release 20061122 (xen-unstable-12502)

["Magnus Damm" <magnus.damm@xxxxxxxxx>]

On 11/29/06, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx> wrote:
> On Wed, 2006-11-29 at 17:17 +0900, Magnus Damm wrote:
> >
> > The kexec tool creates (at load time) one PT_NOTE program header per
> > note exported through /proc/iomem. The number of PT_NOTE program headers
> > is the same as the NR_CPUS constant in the hypervisor.
>
> The guest kernel creates entries in /proc/iomem by calling
> kexec_get_cpu(cpu) until it returns EINVAL. This currently happens when
> cpu>NR_CPUS.
>
> I think this function should return EINVAL for cpu>num_present_cpus()
> instead. Xen doesn't currently do PCPU hotplug and this wouldn't be the
> only thing that would need fixing if it ever does (percpu data would be
> another one I think ;-)).
>
> This would cause the tools to create notes only for CPUs which really
> exist. That would make the loop in machine_crash_kexec() unnecessary.
I feel that using bss instead of per-cpu data is more robust and will
make future cpu hotplug support a breeze to implement - at least in
the case of kexec. Using bss also makes the loop in
machine_crash_kexec() unnecessary.

Using num_present_cpus() will of course work as well, but I'd like to
avoid adding code that likely needs to be rewritten in the near
future.. But you know the future better than I do, so what do you
think? =)

Thanks!

/ magnus

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