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Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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? Thanks > > Thanks, > Laurent >