On 09/08/2021 05:01, Jason Wang wrote: > > 在 2021/8/6 下午3:27, Laurent Vivier 写道: >> On 06/08/2021 08:25, Jason Wang wrote: >>> 在 2021/8/2 下午4:42, Laurent Vivier 写道: >>>> On 02/08/2021 06:50, Jason Wang wrote: >>>>> 在 2021/7/30 上午3:19, Laurent Vivier 写道: >>>>>> Add virtio_queue_disable()/virtio_queue_enable() to disable/enable a >>>>>> queue >>>>>> by setting vring.num to 0 (or num_default). >>>>>> This is needed to be able to disable a guest driver from the host side >>>>> I suspect this won't work correclty for vhost. >>>> With my test it seems to work with vhost too. >>> >>> So setting 0 will lead -EINVAL to be returned during VHOST_SET_VRING_NUM. I >>> think qemu >>> will warn the failure in this case. >> I didn't see any error when I tried. I will check the code. >> >>> What's more important, it's not guaranteed to work for the case of >>> vhost-user or >>> vhost-vDPA. >> Perhaps we can target only the vhost host case, as this is used for failover >> and usually >> the virtio-net device is backed by a bridge on same network as the VFIO >> device? > > > Probably not, it should be a general feature that can work for all types of > virtio/vhost > backends. > > >> >>> >>>>> And I believe we should only do this after the per queue >>>>> enabling/disabling is supported >>>>> by the spec. >>>>> >>>>> (only MMIO support that AFAIK) >>>> I don't want to modify the spec. >>>> >>>> I need something that works without modifying existing (old) drivers. >>>> >>>> The idea is to be able to disable the virtio-net kernel driver from QEMU >>>> if the driver is >>>> too old (i.e. it doesn't support STANDBY feature). >>>> >>>> Setting vring.num to 0 forces the kernel driver to exit on error in the >>>> probe function. >>>> It's what I want: the device is present but disabled (the driver is not >>>> loaded). >>>> >>>> Any other suggestion? >>> >>> I think we should probably disable the device instead of doing it per >>> virtqueue. >>> >> I tried to use virtio_set_disabled() but it doesn't work. >> Perhaps it's too late when I call the function (I need to do that in >> virtio_net_set_features()). What I want is to prevent the load of the driver >> in the guest >> kernel to hide the virtio-net device. Setting vring.num to 0 triggers an >> error in the >> driver probe function and prevents the load of the driver. > > > How about fail the validate_features() in this case?
It's a good suggestion and it seems to work. I'm going to send an updated patch. Thanks, Laurent
