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    SubjectRe: Xen & VMI?
    Chris Wright wrote:
    > I agree that changing the interface to the low-level platform is tricky
    > and less isolated. But how does the VMI protect you from those changes?
    > It simply doesn't, the changes are still necessary. And the inflexibility
    > means the tough corner cases swept under the VMI rug are more difficult
    > to debug, get right, etc...

    I actually disagree here. Yes, it will change over time. VMI was
    designed to be extensible and flexible - you can omit implementation for
    any calls you don't require, and with consensus, you can add new flags,
    fields, and calls where you need them. But VMI as it stands today is
    simply not sufficient to support the hypervisors which are here now.
    There are gaps, particularly with SMP support, which require significant
    changes to either the hypervisors, the kernel, or the VMI itself. There
    are many reasons these gaps still exist, but most prominently, the big
    reason is that nobody wanted to use a single ABI to interface to the
    hypervisor a year ago when we first proposed the VMI interface as a
    virtualization solution for Linux. In the end, I see no reason the
    technical issues can't be solved, but the larger questions about the
    future evolution of the interface and also some largely non-technical
    points, valid or not, have stalled the growth which we originally desired.

    At this point, the question of whether to pursue a common ABI is no
    longer a technical issue, it's no longer a management or evolutionary
    issue at all. It's a pragmatic issue about getting code that works into
    Linux today. It's about working together using what we have as a base,
    which is paravirt-ops, to get working code to users. We can always
    evolve the code in tree if we find a workable cross-vendor ABI that
    solves everyone's problems. But that is neither here nor there, because
    it isn't here today.

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