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Re: [Xen-devel] Re: [RFC] [PATCH] sysfs support for Xen attributes

Dave Hansen wrote:

The ppc64 hypervisor does something like this today in a couple of
places.  It is kinda a mess.  I think that putting a generic, binary
firmware interface leads to having a bit of a crutch.  It basically lets
the userspace software stack bypass Linux and talk directly to the
hypervisor.  It also means that you have to have a very specialized
software stack for each hypervisor or virtualization type, which is very

This pushes things out to userspace, which is generally good.  But, it
is pushing behavior and "hardware" knowledge out there, too.  The
hardware knowledge, especially, is something that we usually try to
The Xen virtual hardware is exposed in the normal way (there is a Xen bus so Xen devices show up under that).

Also things like inter-partition page sharing, and partition migration
are used in other hypervisors.  I think it is essential to get common
interfaces to those things.
In very, very different ways though.

One last thing...  When you say "very strongly binary" do you mean, "are
implemented now as very strongly binary", or "absolutely 100% have to be
horribly strongly binary"?  They are two quite different things. :)
To expose the hypercalls to userspace via sysfs (or another high level interface) would require a whole bunch of complex code to encode the hypercalls and decode there results. I'm not sure having a common interface is a compelling argument to justify this kernel-level complexity since one can just standardize on a userspace library (something like http://www.libvir.org).

I do agree we need a common interface though...


Anthony Liguori

-- Dave

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