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Re: [Qemu-devel] [RFC PATCH] pc: change default machine model and versio
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [RFC PATCH] pc: change default machine model and versions |
Date: |
Tue, 10 Apr 2012 09:09:22 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Sun, Apr 08, 2012 at 08:30:47AM -0400, Ayal Baron wrote:
>
>
> ----- Original Message -----
> > N.B. This is a small patch with significant implications. Please
> > read
> > carefully.
> >
> > Right now, '-M pc' is the default and, in general, this machine type
> > has guest
> > visible ABI changes in each version of QEMU. At some point in each
> > release,
> > we create a '-M pc-X.Y' corresponding to the last release and attempt
> > to make
> > that look like the previous QEMU version's machine.
> >
> > We've accumulated a bunch of '-M pc-X.Y's at this point and if we
> > move to a
> > three month release process, the problem will get much worse.
>
> I agree that every 3 months seems excessive but moving from this to every 24
> months seems to me to be taking it too far (and would cause too many
> problems).
> There is a balance to be struck here and I think it should be somewhere
> between 6 and 12 months.
> Take for example a qemu released 6 month before V2.0 and another one released
> 3 months before V2.0, assuming the latter has some changes in it so that
> pc-next means something else, in order to be able to migrate a VM between
> them I'd need to use -M pc1.0 which would be at least 21 months old and not
> be able to use any of the features introduced during this time.
Indeed, this does seem like rather a long gap between versions.
I can understand the desire to minimize the number of machine
type versions we need to support, but this does seem like going
a bit too far in the other direction
> I have little doubt this would not hold water downstream where we'd have to
> have a compatibility version per minor RHEL release.
I presume that regardless of what QEMU does here, RHEL will still end
up defining its own machine types & ignoring QEMUs, due to the need to
backport features from across releases.
Daniel
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- [Qemu-devel] [RFC PATCH] pc: change default machine model and versions, Anthony Liguori, 2012/04/03
- Re: [Qemu-devel] [RFC PATCH] pc: change default machine model and versions, Eric Blake, 2012/04/05
- Re: [Qemu-devel] [RFC PATCH] pc: change default machine model and versions, Avi Kivity, 2012/04/08
- Re: [Qemu-devel] [RFC PATCH] pc: change default machine model and versions, Ayal Baron, 2012/04/08
- Re: [Qemu-devel] [RFC PATCH] pc: change default machine model and versions,
Daniel P. Berrange <=
- Re: [Qemu-devel] [RFC PATCH] pc: change default machine model and versions, Andreas Färber, 2012/04/10
- Re: [Qemu-devel] [RFC PATCH] pc: change default machine model and versions, Anthony Liguori, 2012/04/10
- Re: [Qemu-devel] [RFC PATCH] pc: change default machine model and versions, Andreas Färber, 2012/04/10