From 542fa14530022044ab577c543fba83202d52b703 Mon Sep 17 00:00:00 2001

From: Amit Shah <amit.shah@redhat.com>

Date: Mon, 21 Mar 2011 22:05:10 +0100

Subject: [PATCH] char: Throttle when host connection is down#

When the host-side connection goes down, throttle the virtio-serial bus

and later unthrottle when a connection gets established.  This helps

prevent any lost IO (guest->host) while the host connection was down.

Bugzilla: 621484

This commit actually helps the bug mentioned above as no writes will now

get lost because of the throttling done here.  With just the patches

sent earlier for that bug, one write will end up getting lost in the

worst case (host d/c, guest write, host connect).

Signed-off-by: Amit Shah <amit.shah@redhat.com>

Signed-off-by: Cole Robinson <crobinso@redhat.com>

---

 qemu-char.c | 14 ++++++++++++++

 1 file changed, 14 insertions(+)

diff --git a/qemu-char.c b/qemu-char.c

index 9f8608a..bfc94a5 100644

--- a/qemu-char.c

+++ b/qemu-char.c

@@ -140,6 +140,9 @@ static void qemu_chr_generic_open_bh(void *opaque)

 {

     CharDriverState *s = opaque;

     qemu_chr_be_event(s, CHR_EVENT_OPENED);

+    if (s->write_blocked) {

+        char_write_unblocked(s);

+    }

     qemu_bh_delete(s->bh);

     s->bh = NULL;

 }

@@ -2244,6 +2247,17 @@ static int tcp_chr_write(CharDriverState *chr, const uint8_t *buf, int len)

         ret = send_all(chr, s->fd, buf, len);

         if (ret == -1 && errno == EPIPE) {

             tcp_closed(chr);

+

+            if (chr->chr_enable_write_fd_handler && chr->chr_write_unblocked) {

+                /*

+                 * Since we haven't written out anything, let's say

+                 * we're throttled.  This will prevent any output from

+                 * the guest getting lost if host-side chardev goes

+                 * down.  Unthrottle when we re-connect.

+                 */

+                chr->write_blocked = true;

+                return 0;

+            }

         }

         return ret;

     } else {

-- 

1.7.12.1