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>

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