Re: [Qemu-devel] [PATCH 3/3 v2] Add a pc-0-10 machine type for compatibility with 0.10.x

[Anthony Liguori]

Gerd Hoffmann wrote:
> On 07/08/09 12:48, Mark McLoughlin wrote:
> > Add a pc-0-10 machine type to allow a pc machine to be created with
> > virtio block and console devices compatibility with qemu-0.10.x.
>
> > +enum {
> > +    COMPAT_DEFAULT = 0,
> > +    COMPAT_0_10, /* compatible with qemu 0.10.x */
> > +};
>
> Hmm.  Just digged in the virtio blk code.  Noticed some ppc machines 
> have virtio block devices too.  So linking it to a machine type looks 
> wrong to me.

No, it's right.  A machine type is nothing more than a default device 
tree.  If we want to change what the default device tree is and wish to 
maintain compatibility, we need to introduce a new device tree so that 
the old one can be still accessed.

So basically, if we had device config files, it would look like:

/usr/share/qemu/configs/pc-0-10.dts
/usr/share/qemu/configs/pc-0-11.dts
/usr/share/qemu/configs/pc -> /usr/share/qemu/configs/pc-0-11.dts

For other board types, they would also need to version their device 
trees too.

> Another question:  Is migrating from 0.11 in 0.10-compat mode to 0.10 
> supposed to work?  If so we make virtio-net better turn off msi then.

If you mean live migration, no.  However, live migration from 0.10 to 
0.11 in 0.10-compat mode should work.

But from the guest perspective, 0.10-compat mode should look identical 
to 0.10 which means we do want to turn off msi.

Regards,

Anthony Liguori

> cheers,
>   Gerd