Merge remote-tracking branch 'remotes/amit/tags/vser-for-2.3-3' into staging

virtio-serial api: guest_writable callback for users

# gpg: Signature made Thu Mar 19 12:06:55 2015 GMT using RSA key ID 854083B6
# gpg: Good signature from "Amit Shah <amit@amitshah.net>"
# gpg:                 aka "Amit Shah <amit@kernel.org>"
# gpg:                 aka "Amit Shah <amitshah@gmx.net>"

* remotes/amit/tags/vser-for-2.3-3:
  virtio: serial: expose a 'guest_writable' callback for users

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

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)

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 end being
+         * connected.
+         */
+    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