On Thu, 03 Nov 2011 10:33:23 +0200, Sasha Levin <levinsasha928@xxxxxxxxx> wrote: > On Thu, 2011-11-03 at 12:28 +1030, Rusty Russell wrote: > > 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. Exactly. But we haven't had a problem so far; but we don't put arbitrarily large fields in there. > 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. But the drivers currently just use offsetof() to access it, eg: if (virtio_config_val_len(vdev, VIRTIO_NET_F_MAC, offsetof(struct virtio_net_config, mac), dev->dev_addr, dev->addr_len) < 0) That would have to change, and that means a change for drivers and for the non-PCI implementations. Hence I think this is a step too far. > > 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. The seabios guys will definitely thank you! Cheers, Rusty. -- 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
