On (Thu) 19 Mar 2015 [11:21:04], Markus Armbruster wrote:
> Amit Shah <amit.s...@redhat.com> writes:
>
> > Users of virtio-serial may want to know when a port becomes writable. A
> > port can stop accepting writes if the guest port is open but not being
> > read from. In this case, data gets queued up in the virtqueue, and
> > after the vq is full, writes to the port do not succeed.
> >
> > When the guest reads off a vq element, and adds a new one for the host
> > to put data in, we can tell users the port is available for more writes,
> > via the new ->guest_writable() callback.
> >
> > Signed-off-by: Amit Shah <amit.s...@redhat.com>
> >
> > ---
> >
> > Well I forgot to send this out for 2.3; I was waiting for the window to
> > open, and totally forgot about it when it was open. Since this adds an
> > internal API, and there's no chance of regressions, I propose we include
> > this in 2.3.
>
> Yes, it's just an internal interface, and the risk is very low (new code
> runs, but it looks harmless enough). However, I don't see a pressing
> need for 2.3 as long as there are no users of the new interface.
Marc-Andre has written a spice consumer for this; and that has been on
hold because this patch hadn't gone in. It's just my fault for
dropping this one..
>
> > v4: fixed tabs in indentation (kraxel)
> > v3: document the semantics of the callback (Peter Maydell, Markus)
> > v2: check for port != NULL (Peter Maydell)
> > ---
> > hw/char/virtio-serial-bus.c | 31 +++++++++++++++++++++++++++++++
> > include/hw/virtio/virtio-serial.h | 11 +++++++++++
> > 2 files changed, 42 insertions(+)
> >
> > diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
> > index c86814f..d14e872 100644
> > --- a/hw/char/virtio-serial-bus.c
> > +++ b/hw/char/virtio-serial-bus.c
> > @@ -465,6 +465,37 @@ static void handle_output(VirtIODevice *vdev,
> > VirtQueue *vq)
> >
> > static void handle_input(VirtIODevice *vdev, VirtQueue *vq)
> > {
> > + /*
> > + * Users of virtio-serial would like to know when guest becomes
> > + * writable again -- i.e. if a vq had stuff queued up and the
> > + * guest wasn't reading at all, the host would not be able to
> > + * write to the vq anymore. Once the guest reads off something,
> > + * we can start queueing things up again. However, this call is
> > + * made for each buffer addition by the guest -- even though free
> > + * buffers existed prior to the current buffer addition. This is
> > + * done so as not to maintain previous state, which will need
> > + * additional live-migration-related changes.
> > + */
> > + VirtIOSerial *vser;
> > + VirtIOSerialPort *port;
> > + VirtIOSerialPortClass *vsc;
> > +
> > + vser = VIRTIO_SERIAL(vdev);
> > + port = find_port_by_vq(vser, vq);
> > +
> > + if (!port) {
> > + return;
> > + }
> > + vsc = VIRTIO_SERIAL_PORT_GET_CLASS(port);
> > +
> > + /*
> > + * If guest_connected is false, this call is being made by the
> > + * early-boot queueing up of descriptors, which is just noise for
> > + * the host apps -- don't disturb them in that case.
> > + */
> > + if (port->guest_connected && port->host_connected &&
> > vsc->guest_writable) {
> > + vsc->guest_writable(port);
> > + }
> > }
> >
> > static uint32_t get_features(VirtIODevice *vdev, uint32_t features)
> > diff --git a/include/hw/virtio/virtio-serial.h
> > b/include/hw/virtio/virtio-serial.h
> > index ccf8459..a275199 100644
> > --- a/include/hw/virtio/virtio-serial.h
> > +++ b/include/hw/virtio/virtio-serial.h
> > @@ -60,6 +60,17 @@ typedef struct VirtIOSerialPortClass {
> > /* Guest is now ready to accept data (virtqueues set up). */
> > void (*guest_ready)(VirtIOSerialPort *port);
> >
> > + /*
> > + * Guest has enqueued a buffer for the host to write into.
> > + * Called each time a buffer is enqueued by the guest;
> > + * irrespective of whether there already were free buffers the
> > + * host could have consumed.
> > + *
> > + * This is dependent on both, the guest and host ends being
> > + * connected.
>
> Sounds awkward. Perhaps: This is dependent on both the guest and
> thehost end being connected.
or an added comma? I think it can go in later as a cleanup if this
patch goes in; I already sent pull req before seeing this mail..
> > + */
> > + void (*guest_writable)(VirtIOSerialPort *port);
> > +
> > /*
> > * Guest wrote some data to the port. This data is handed over to
> > * the app via this callback. The app can return a size less than
>
> The code looks good to me, but the interface is a bit hard to judge for
> virtio noobs like me without an actual user. But since it's not an
> external interface:
>
> Reviewed-by: Markus Armbruster <arm...@redhat.com>
Thanks, and Marc-Andre has confirmed it works for the spice use-case
(they were the ones who asked for this).
Amit
