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Message-ID: <47322262.8000101@gmail.com>
Date: Wed, 07 Nov 2007 15:38:58 -0500
From: Gregory Haskins <gregory.haskins.ml@...il.com>
To: Avi Kivity <avi@...ranet.com>
CC: Gregory Haskins <gregory.haskins.ml@...il.com>,
Anthony Liguori <aliguori@...ibm.com>,
Rusty Russell <rusty@...tcorp.com.au>,
Dor Laor <dor.laor@...ranet.com>,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org
Subject: Re: Use of virtio device IDs
Avi Kivity wrote:
>
> I dislike strings. They make it look as if you have a nice extensible
> interface, where in reality you have a poorly documented interface which
> leads to poor interoperability.
Its not really a full fledged interface, but rather just a simple id
mechanism. A decentralized id mechanism with less administrative burden.
On the flip side, a centralized namespace has the advantage of
controlling collisions at the expense of administrative overhead. After
designing systems both ways in the past, I prefer to reduce the admin
burden, but that is just me.
> PCI means that you can reuse all of the platform's infrastructure for
> irq allocation, discovery, device hotplug, and management.
Its tempting to use, yes. However, most of that infrastructure is
completely inappropriate for a PV implementation, IMHO. You are
probably better off designing something that is PV specific instead of
shoehorning it in to fit a different model (at least for the things I
have in mind). Its not a heck of a lot of code to write a pv-centric
version of these facilities.
> You can write it for new guests but backporting it to older guests will be a
> huge task.
>
> We will support non-pci for s390, but in order to support Windows and
> older Linux PCI is necessary.
I don't know if I would agree with "necessary". "Easier" perhaps. ;) By
definition once you are PV you are hypervisor aware. Now its just a
matter of plugging in the appropriate plumbing to bridge the hypervisor
to the guest-os. Some might be easier than others, sure. But all
should be extensible to a degree.
But I digress. I haven't really had much of a chance to follow the
latest developments here as I have been lost in -rt land for a few
months now. But I know Anthony and Rusty are top-notch, so I'm sure you
guys have it under control. Hopefully, one day soon I will be able to
join you guys again (perhaps to the KVM team's dismay ;).
Regards,
-Greg
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