Re: [PATCH 2 of 2] Use CONFIG_PREEMPT_NOTIFIERS around struct preempt_notifier

[Hollis Blanchard <hollisb-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

On Wed, 2008-01-16 at 10:08 +0200, Avi Kivity wrote:
> Hollis Blanchard wrote:
> > # HG changeset patch
> > # User Hollis Blanchard <hollisb-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> > # Date 1200434370 21600
> > # Node ID 9878c9cec5f831ff5e9b97539aabc5fa3d934501
> > # Parent  931a81e1002110be0e8bf5b335bf199d43534c2c
> > This allows kvm_host.h to be #included even when struct preempt_notifier is
> > undefined.
> 
> Don't you actually need preempt notifiers?  They are useful if you have 
> state that is only needed from userspace, but is expensive to switch.  
> For x86, this is the syscall msrs (which define the syscall entry 
> point), the fpu (which is not used in the kernel), and a few other bits 
> (which I'm too lazy too look up and are esoteric anyway).

Yes, I do. However, if you #include <kvm_host.h> *without*
CONFIG_VIRTUALIZATION=y, CONFIG_PREEMPT_NOTIFIERS is not set and the
structure is undefined.

It is Linux policy to be able to unconditionally include headers, and
indeed I already hit this problem when I added that #include to
arch/powerpc/kernel/asm-offsets.c.

-- 
Hollis Blanchard
IBM Linux Technology Center


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