Re: [Qemu-devel] [PATCH] Migration compatibility for serial

[Michael S. Tsirkin]

On Wed, Jun 17, 2015 at 01:55:37PM +0200, Paolo Bonzini wrote:
> 
> 
> On 17/06/2015 13:54, Michael S. Tsirkin wrote:
> >>> > >> > Where, in the specific case of migration?
> > > > Just look at hour compat flags.
> > > > 
> > > > For example (intentionally using serial here):
> > > >         {\
> > > >             .driver   = "pci-serial",\
> > > >             .property = "prog_if",\
> > > >             .value    = stringify(0),\
> > > >         },\
> > > >         {\
> > > >             .driver   = "pci-serial-2x",\
> > > >             .property = "prog_if",\
> > > >             .value    = stringify(0),\
> > > >         },\
> > > >         {\
> > > >             .driver   = "pci-serial-4x",\
> > > >             .property = "prog_if",\
> > > >             .value    = stringify(0),\
> > > >         },\
> > > > 
> > > > apparently some clients check the specific prog if
> > > > value, completely breaking if the value was incorrect.
> > > > So we fixed it for new machine types but not old ones.
> > > 
> > > That has nothing to do with migration.
> > 
> > If you change prog_if migration fails.
> 
> No, it doesn't.  The guest misbehaves maybe, but the migration format is
> not affected.
> 
> Paolo

I just tried, set prog_if to different values, sure it failed.

Here's another one, at random:

Author: Michael S. Tsirkin <address@hidden>
Date:   Thu Feb 14 19:11:27 2013 +0200

    e1000: unbreak the guest network migration to 1.3
    
    QEMU 1.3 does not emulate the link auto negotiation, so if migrate to a
    1.3 machine during link auto negotiation, the guest link will be set to 
down.
    Fix this by just disabling auto negotiation for 1.3 and older.
    
    Signed-off-by: Michael S. Tsirkin <address@hidden>


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MST