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? > > >> >>> 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. Thanks, Laurent
