Il 25/09/2013 09:49, Michael S. Tsirkin ha scritto:
>> > +
>> > +8. The DRIVER_OK status bit is set. This is simply informational,
>> > + as the device may already be active at this point.
>
> So we have a separate issue I think: there's lots
> of device specific configuration that really
> would benefit from "OK now go" bit.
>
> For example, we register network device and we
> really don't want e.g. config interrupts before that is done.
>
> Also qemu relied on DRIVER_OK to kick off vhost net and
> vhost scsi.
True, but that is wrong. The virtio-scsi driver had to be modified to
support vhost-scsi, because it used the virtqueues before setting
DRIVER_OK and this didn't work with vhost-scsi. This was ugly.
The right thing to do would be to start vhost upon the driver setting
FEATURES_OK. Failure to start vhost (which is fatal for vhost-scsi,
since there is no userspace fallback unlike vhost-net) could be reported
by not acknowledging FEATURES_OK.
Paolo
