Re: [Qemu-devel] Re: [PATCH v2 12/15] monitor: Add basic device state visualization

[Avi Kivity]

On 05/25/2010 04:03 PM, Anthony Liguori wrote:
> > > I don't think that qdev device names and paths are something we have 
> > > to worry much about changing over time since they reflect logical 
> > > bus layout.  They should remain static provided the devices remain 
> > > static.
> >
> > Modulo mistakes.  We already saw one (lack of pci domains).  To 
> > reduce the possibility of mistakes, we need reviewable documentation.
>
>
> pci domains was only a mistake as a nice-to-have.  We can add pci 
> domains in a backwards compatible way.

It adds a new level to the qdev tree.  Of course we can hide the new 
level for older clients, and newer clients can drop the level for older 
qemus, but it will be oh-so-painful.

> The arguments you're making about the importance of backwards 
> compatibility and what's needed to strongly guarantee it are equally 
> applicable to the live migration protocol.  We really do need to 
> formally document the live migration protocol in such a way that it's 
> reviewable if we hope to truly make it compatible across versions.

Mostly agreed.  I think live migration has a faster/easier deprecation 
schedule (easier not to support migration from 0.n-k to 0.n than to 
remove qmp support for a feature introduced in 0.n-k when releasing 
0.n).  But that's a minor concern, improving our externally visible 
interface documentation is a good thing and badly needed.

--
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