On 05/06/2017 06:21 AM, Michael S. Tsirkin wrote: > On Thu, Apr 27, 2017 at 02:33:44PM +0800, Wei Wang wrote: > > On 04/14/2017 01:08 AM, Michael S. Tsirkin wrote: > > > On Thu, Apr 13, 2017 at 05:35:08PM +0800, Wei Wang wrote: > > > > Add a new vq, miscq, to handle miscellaneous requests between the > > > > device and the driver. > > > > > > > > This patch implemnts the > VIRTIO_BALLOON_MISCQ_INQUIRE_UNUSED_PAGES > > > implements > > > > > > > request sent from the device. > > > Commands are sent from host and handled on guest. > > > In fact how is this so different from stats? > > > How about reusing the stats vq then? You can use one buffer for > > > stats and one buffer for commands. > > > > > > > The meaning of the two vqs is a little different. statq is used for > > reporting statistics, while miscq is intended to be used to handle > > miscellaneous requests from the guest or host > > misc just means "anything goes". If you want it to mean "commands" name it so. Ok, will change it. > > (I think it can > > also be used the other way around in the future when other new > > features are added which need the guest to send requests and the host > > to provide responses). > > > > I would prefer to have them separate, because: > > If we plan to combine them, we need to put the previous statq related > > implementation under miscq with a new command (I think we can't > > combine them without using commands to distinguish the two features). > > Right. > > In this way, an old driver won't work with a new QEMU or a new driver > > won't work with an old QEMU. Would this be considered as an issue > > here? > > Compatibility is and should always be handled using feature flags. There's a > feature flag for this, isn't it? The negotiation of the existing feature flag, VIRTIO_BALLOON_F_STATS_VQ only indicates the support of the old statq implementation. To move the statq implementation under cmdq, I think we would need a new feature flag for the new statq implementation: #define VIRTIO_BALLOON_F_CMDQ_STATS 5 What do you think? Best, Wei
