From 33f3874dc760f0960d408be2f916d04373de543b 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>

Signed-off-by: Cole Robinson <crobinso@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 dd6f614..0e12514 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)