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Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions |
Date: |
Wed, 10 Jun 2009 20:03:06 +0300 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Wed, Jun 10, 2009 at 05:46:03PM +0100, Paul Brook wrote:
> > > If you can't create an identical machine from scratch then I don't
> > > consider snapshot/migration to be a useful feature. i.e. as soon as you
> > > shutdown and restart the guest it is liable to break anyway.
> >
> > Why is liable to break?
>
> A VM booted on an old version of qemu and migrated to a new version will
> behave differently to a the same VM booted on a new version of qemu.
It will behave identically. That's what the patch does: discover
how did the device behave on old qemu, and make it behave the same way
on new qemu.
> I hope I don't need to explain why this is bad.
>
> As previously discussed, any guest visible changes are liable to break a
> guest
> OS, particularly guests like Windows which deliberately break when run on
> "different" hardware. Personally I don't particularly care, but if we support
> live migration we also need to support "cold" migration - i.e. shutdown and
> restart.
>
> >So once you load and image with MSIX capability off,
> >it will stay off across guest restarts.
>
> I'm assuming guest restart includes restarting qemu.
>
> Paul
If you restart qemu, and load an image, what we should do is look at the
image and behave in a way consistent with how the qemu that created the
image behaved. If you load an image, you switch to a VM, and should be
consistent with the VM you just loaded. And we do not need a flag or a
machine description file to tell us this.
--
MST
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, (continued)
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/11