>From 8750ea70a68e74ca3ecea6149d1d5289cc77dae3 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 08/28] 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 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/hw/virtio-console.c b/hw/virtio-console.c
index cfc3087..b91f46e 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)
@@ -99,6 +109,7 @@ 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)
-- 
1.7.5.1