On Thu, 2011-11-03 at 12:28 +1030, Rusty Russell wrote: > On Wed, 02 Nov 2011 20:49:27 +0200, Sasha Levin <levinsasha928@xxxxxxxxx> 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. Old layouts won't have the new virtio-pci cap structure in their PCI config space. > 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. Variable length config wasn't used yet because space in the device specific space was reserved for a feature even if that feature wasn't used. For example, the MAC feature reserved 6 bytes in the config space for the MAC even if VIRTIO_NET_F_MAC wasn't enabled. Here we can just avoid having it pollute the config space until it's enabled. I don't think it'll have any impact on non-PCI implementations since the "pointers" are simply offsets from the beginning of the config space, and are not PCI specific in any way. > 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. Yup, we can do that. -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
