Re: [Qemu-devel] [PATCH 2/2] virtio-serial-bus: query guest features after guest sets them

[Michael S. Tsirkin]

On Mon, Apr 23, 2012 at 02:26:24PM +0300, Alon Levy wrote:
> From: Amit Shah <address@hidden>
> 
> Currently we query the virtio features w/o even waiting
> for the guest to boot up and ack features.
> 
> Do the querying after set_features has succeeded.
> 
> The check to enable guest_connected for the host to be able to write to
> the guest was flawed in this way, causing all ports to be initialised
> with the 'guest_connected' status to on.
> 
> Signed-off-by: Amit Shah <address@hidden>
> ---
>  hw/virtio-serial-bus.c |   26 ++++++++++++++++++--------
>  1 file changed, 18 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
> index e22940e..90b3674 100644
> --- a/hw/virtio-serial-bus.c
> +++ b/hw/virtio-serial-bus.c
> @@ -512,6 +512,23 @@ static uint32_t get_features(VirtIODevice *vdev, 
> uint32_t features)
>      return features;
>  }
>  
> +static void set_features(VirtIODevice *vdev, uint32_t features)
> +{
> +    VirtIOSerial *vser;
> +    VirtIOSerialPort *port;
> +
> +    vser = DO_UPCAST(VirtIOSerial, vdev, vdev);
> +    port = find_port_by_id(vser, 0);
> +
> +    if (port && !use_multiport(vser)) {
> +        /*
> +         * Allow writes to guest in this case; we have no way of
> +         * knowing if a guest port is connected.
> +         */
> +        port->guest_connected = true;
> +    }
> +}
> +
>  /* Guest requested config info */
>  static void get_config(VirtIODevice *vdev, uint8_t *config_data)
>  {
> @@ -798,14 +815,6 @@ static int virtser_port_qdev_init(DeviceState *qdev)
>          return ret;
>      }
>  
> -    if (!use_multiport(port->vser)) {
> -        /*
> -         * Allow writes to guest in this case; we have no way of
> -         * knowing if a guest port is connected.
> -         */
> -        port->guest_connected = true;
> -    }
> -
>      port->elem.out_num = 0;
>  
>      QTAILQ_INSERT_TAIL(&port->vser->ports, port, next);
> @@ -903,6 +912,7 @@ VirtIODevice *virtio_serial_init(DeviceState *dev, 
> virtio_serial_conf *conf)
>      mark_port_added(vser, 0);
>  
>      vser->vdev.get_features = get_features;
> +    vser->vdev.set_features = set_features;
>      vser->vdev.get_config = get_config;
>      vser->vdev.set_config = set_config;

Problem is I think legacy guests don't call set_features.

A cleaner way is to check on set_status calls. Guest is not connected
until driver_ok is set anyway.

So you would do
        if (!use_multiport(guest)) {
                port->guest_connected = status & VIRTIO_CONFIG_S_DRIVER_OK;
        }

You won't need patch 1/2 in this case either.

> -- 
> 1.7.10
>