On Wed, Oct 02, 2013 at 10:22:13AM +0930, Rusty Russell wrote:
> "Michael S. Tsirkin" <> writes:
> > On Tue, Oct 01, 2013 at 05:42:52PM +0930, Rusty Russell wrote:
> >> "Michael S. Tsirkin" <> writes:
> >> > On Tue, Oct 01, 2013 at 11:19:57AM +0930, Rusty Russell wrote:
> >> >> "Michael S. Tsirkin" <> writes:
> >> >> > On Thu, Sep 26, 2013 at 12:05:19PM +0930, Rusty Russell wrote:
> >> >> >> may be a significant (or infinite) delay before setting this
> >> >> >> bit.
> >> >> >>
> >> >> >> + FEATURES_OK (8) Indicates that the driver has acknowledged all the
> >> >> >> + features it understands, and feature negotiation is complete.
> >> >> >> +
> >> >> >> DRIVER_OK (4) Indicates that the driver is set up and ready to
> >> >> >> drive the device.
> >> >> >>
> >> >> >> @@ -444,23 +447,46 @@ how to communicate with the specific device.
> >> >> >>
> >> >> >> 3. The DRIVER status bit is set: we know how to drive the device.
> >> >> >>
> >> >> >> -4. Device-specific setup, including reading the device feature
> >> >> >> - bits, discovery of virtqueues for the device, optional per-bus
> >> >> >> - setup, and reading and possibly writing the device's virtio
> >> >> >> - configuration space.
> >> >> >> +4. Device feature bits are read, and the the subset of feature bits
> >> >> >> + understood by the OS and driver is written to the device.
> >> >> >> +
> >> >> >> +5. The FEATURES_OK status bit is set.
> >> >> >>
> >> >> >> -5. The subset of device feature bits understood by the driver is
> >> >> >> - written to the device.
> >> >> >> +6. The status byte is re-read to ensure the FEATURES_OK bit is still
> >> >> >> + set: otherwise, the device does not support our subset of features
> >> >> >> + and the device is unusable.
> >> >> >>
> >> >> >> -6. The DRIVER_OK status bit is set.
> >> >> >> +7. Device-specific setup, including discovery of virtqueues for the
> >> >> >> + device, optional per-bus setup, reading and possibly writing the
> >> >> >> + device's virtio configuration space, and population of virtqueues.
> >> >> >>
> >> >> >> -7. The device can now be used (ie. buffers added to the
> >> >> >> - virtqueues)[4]
> >> >> >> +8. The DRIVER_OK status bit is set. At this point the device is
> >> >> >> + "live".
> >> >> >
> >> >> > What exactly does this imply?
> >> >> > Should device consume buffers before it's live, or should
> >> >> > it postpone this until DRIVER_OK?
> >> >>
> >> >> The device MUST NOT consume buffers before DRIVER_OK.
> >> >> - The driver is free to rip those descriptors back out if it wants
> >> >> to clean up and fail, for example.
> >> >>
> >> >> The driver MUST NOT notify the device before DRIVER_OK.
> >> >> - It's not ready yet...
> >> >
> >> > This last one will need checks on data path in driver:
> >> > if (vq->dev->driver_ok)
> >> > vq_kick();
> >> > consider that once we register a netdev it
> >> > can start sending packets.
> >>
> >> That's why the *driver* will need to set DRIVER_OK manually now.
> >
> > OK, but this means driver can fail after DRIVER_OK. Is that OK?
>
> Yes, because that was always true. Due to bugs, or OOM, it may be
> necessary to set FAILED on a device during operation.
OK, in that case DRIVER_OK looks OK to me. So you'll post
the full version so we can OK this change on the next meeting?
> >> I'm thinking Linux would add a BUG_ON(!vq->dev->driver_ok) in
> >> virtqueue_kick().
> >>
> >> Cheers,
> >> Rusty.
> >
> > We can just set vq->broken when vq is created, clear on
> > driver_ok.
>
> That won't give an OOPS, which is what I wanted :)
Then set vq->in_use. It kind of makes sense.
> But we'll come up with something.
>
> Cheers,
> Rusty.
