Re: [libvirt] cpu flags
On Tue, Sep 16, 2008 at 04:45:09PM -0400, Ben Guthro wrote:
Hi,
We're finding that we are going to be needing the cpu flags (as reported
in /proc/cpuinfo)
..specifically to find out if we are a vmx enabled machine.
So - off I went looking into this for a patch to submit upstream.
Unfortunately, I ran into some questions which need answering before I
really proceed with this
It seems to me that this info would best be parsed in src/nodeinfo.c
This is where other cpuinfo things are parsed...and stored in the
nodeinfo struct
Perhaps we store this as a bitmask encoded int, as defined in
/usr/include/asm/cpufeature.h and tack this onto the end of sad struct.
My concern is that adding to the nodeinfo struct breaks the API - such
that the structs will be different sizes between versions.
Indeed - any struct or API in include/libvirt/libvirt.h is immutable
to preserve ABI.
Also - this seems to be x86 specific. Are we primarily destined for
x86?
Or would this type of change be unacceptable due to not working on PPC,
for example?
No,we need to work on every architecture - KVM for example is ported to
x86, ia64, ppc, and s390, Xen is on arm, x86, ia64. Now the set of flags
will likely be different across each processor - and some may not even
have a concept of flags, but we shouldn't be specifically x86 in API.
I think the most likely place for exposing CPU flags would be in the
capabilities XML format. We do in fact already expose 3 flags there,
PAE, VMX and SVM.
As John mentions we also need to be careful to specify a naming that is
consistent across OS - though that may be as simple as defining that
the naming is required to match Linux /proc/cpuinfo standards. The intent
is that if you have the same CPUs in 2 machines, one running Linux and
the other Solaris then libvirt must report the same names.
Regards,
Daniel
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