On Thu, Jul 25, 2013 at 09:50:21AM +0100, Peter Maydell wrote: > On 25 July 2013 06:38, Michael S. Tsirkin <m...@redhat.com> wrote: > > On Fri, Jul 12, 2013 at 09:36:57PM +0100, Peter Maydell wrote: > >> The MMIO virtio transport spec allows the guest to tell the host how > >> large the queue size is. Add virtio_queue_set_num() function which > >> implements this in the QEMU common virtio support code. > >> > >> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> > > > > Probably needs to go back to default value on reset? > > Tricky, since the default value is "whatever was passed to > virtio_add_queue()" and we don't save that anywhere. > > For virtio-mmio it is a guest bug to fail to write to the > QueueNum register, so the current behaviour is not out of > specification (and not harmful either AFAICT).
Best not to leak info across reboots. Also if guest sets num = 0 it will cause all kind of harm, no? > I guess we could add a vring.defaultnum, which would be > set by virtio_add_queue/virtio_del_queue, and have reset > copy defaultnum into num. No migration needed for defaultnum > because it's always the same for a particular qemu config. Sounds good. > > Need to migrate? > > It's already migrated (though I'm not entirely sure why). > > > Is the default value a max legal value? If yes probably a good > > idea to enforce this. > > virtio_add_queue() already enforces this -- it will abort() > if you try to set up a queue with a default size greater > than VIRTQUEUE_MAX_SIZE. No I mean does default value have some meaning? Does host supply a hint of a max value besides VIRTQUEUE_MAX_SIZE? > > thanks > -- PMM
