Re: [PATCH V2 2/2] virtio: introduce STOP status bit

[Jason Wang <jasowang@redhat.com>]

在 2021/7/11 上午4:40, Michael S. Tsirkin 写道:
> On Tue, Jul 06, 2021 at 12:33:34PM +0800, Jason Wang wrote:
> > This patch introduces a new status bit STOP. This will be
> > used by the driver to stop the device in order to safely fetch the
> > device state (virtqueue state) from the device.
> >
> > This is a must for supporting migration.
> >
> > Signed-off-by: Jason Wang<jasowang@redhat.com>
> So I feel that if the point is to be able to build a
> feature that is useful beyond live migration then this
> kind of misses the mark. For example the serial device
> for a while now wanted a way to take back buffers
> added to a given VQ. If you are working on a way for*driver*
> to stop the VQs then let us make it useful for this ...


I'm a little bit confused.

If it's not for migration and not for the VMM to track the buffer. The 
drivers itself should have the sufficient knowledge for the buffers that 
is consumed by not made used.

What missed here is just the way to "stop" or "freeze" the device. With 
this status, the driver can use its own knowledge to take back buffers 
since we know it will be safe (device won't use those buffers any mroe).

Thanks


>