Re: virtio-pci new configuration proposal

[Rusty Russell <rusty@rustcorp.com.au>]

On Wed, 02 Nov 2011 20:49:27 +0200, Sasha Levin <levinsasha928@gmail.com> wrote:
> This is a proposal for a new layout of the virtio-pci config space.
> 
> We will separate the current configuration into two: A virtio-pci common
> configuration and a device specific configuration. This allows more flexibility
> with adding features and makes usage easier, specifically in cases like the
> ones in virtio-net where device specific configurations depend on device
> specific features.

Thanks for this Sasha.  Several general comments:

1) How to we distinguish the two layouts?  In theory, we need to do this
   forever.  In practice we can deprecate the old layout in several
   years' time.

2) I don't think we want to turn the device-specific config into a
   linked list.  We haven't needed variable-length config (yet!), and
   it's (slightly) more complex.  That's also the part of the spec which
   is shared with non-PCI virtio implementations.

3) If we're changing the queue layout, it's a chance to fix a
   longstanding bug: let the guest notify the host of preferred
   queue size and alignment.

Cheers,
Rusty.