From 596c901c52b211425afe4d40e361d3ee1e5ec4bc Mon Sep 17 00:00:00 2001
From: Amit Shah <amit.shah@redhat.com>
Date: Mon, 21 Mar 2011 22:06:41 +0100
Subject: [PATCH] virtio-console: Enable port throttling when chardev is slow
 to consume data

When a chardev indicates it can't accept more data, we tell the
virtio-serial code to stop sending us any more data till we tell
otherwise.  This helps in guests continuing to run normally while the vq
keeps getting full and eventually the guest stops queueing more data.
As soon as the chardev indicates it can accept more data, start pushing!

Signed-off-by: Amit Shah <amit.shah@redhat.com>
---
 hw/virtio-console.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/hw/virtio-console.c b/hw/virtio-console.c
index 066590c..2b5e515 100644
--- a/hw/virtio-console.c
+++ b/hw/virtio-console.c
@@ -20,6 +20,16 @@ typedef struct VirtConsole {
     CharDriverState *chr;
 } VirtConsole;
 
+/*
+ * Callback function that's called from chardevs when backend becomes
+ * writable.
+ */
+static void chr_write_unblocked(void *opaque)
+{
+    VirtConsole *vcon = opaque;
+
+    virtio_serial_throttle_port(&vcon->port, false);
+}
 
 /* Callback function that's called when the guest sends us data */
 static ssize_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
@@ -110,6 +120,7 @@ static const QemuChrHandlers chr_handlers = {
     .fd_can_read = chr_can_read,
     .fd_read = chr_read,
     .fd_event = chr_event,
+    .fd_write_unblocked = chr_write_unblocked,
 };
 
 static int virtconsole_initfn(VirtIOSerialPort *port)
-- 
1.7.11.2