Re: [Qemu-devel] [PATCH] qemu-options: document existance of versioned machine types

[Daniel P. Berrange]

On Tue, Jul 25, 2017 at 01:46:23PM -0400, John Snow wrote:
> 
> 
> On 07/25/2017 10:10 AM, Daniel P. Berrange wrote:
> > The -machine docs did not explain what the versioned machine
> > types are for, nor that they'll be maintained across
> > releases.
> > 
> > Signed-off-by: Daniel P. Berrange <address@hidden>
> > ---
> >   qemu-options.hx | 15 ++++++++++++++-
> >   1 file changed, 14 insertions(+), 1 deletion(-)
> > 
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 746b5fa75d..9f6e2adfff 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -49,7 +49,20 @@ STEXI
> >   @item -machine address@hidden,address@hidden,...]]
> >   @findex -machine
> >   Select the emulated machine by @var{name}. Use @code{-machine help} to 
> > list
> > -available machines. Supported machine properties are:
> > +available machines.
> > +
> > +For architectures which aim to support live migration compatibility
> > +across releases, each release will introduce a new versioned machine
> > +type. For example, the 2.8.0 release introduced machine types
> > +``pc-i440fx-2.8'' and ``pc-q35-2.8'' for the x86_64/i686 architectures.
> > +
> > +To allow live migration of guests from QEMU version 2.8.0, to QEMU
> > +version 2.9.0, the 2.9.0 version must support the ``pc-i440fx-2.8''
> > +and ``pc-q35-2.8'' machines too. To allow users live migrating VMs
> > +to skip multiple intermediate releases when upgrading, new releases
> > +of QEMU will support machine types from many previous versions.
> > +
> > +Supported machine properties are:
> >   @table @option
> >   @item address@hidden:@var{accels2}[:...]]
> >   This is used to enable an accelerator. Depending on the target 
> > architecture,
> > 
> 
> Seems like an improvement to me, but do we have any formal policy on how
> long we support said machine types? The new wording prompts that question.

I wasn't going to mention that in this patch, to avoid delay on getting it
merged. I was going to send a further patch that makes it explicit that we
will never delete machine types for as long as any active QEMU contributor
has need for them in downstream version they maintain

> Reviewed-by: John Snow <address@hidden>

Regards,
Daniel
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