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From 3d48415578c65490675616d41a32a1e9e3a71f43 Mon Sep 17 00:00:00 2001
From: "Daniel P. Berrange" <>
Date: Thu, 8 Feb 2018 17:50:34 +0100
Subject: [PATCH 20/27] ui: correctly reset framebuffer update state after
 processing dirty regions
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RH-Author: Daniel P. Berrange <>
Message-id: <>
Patchwork-id: 78941
O-Subject: [RHEL-7.5 qemu-kvm PATCH v1 20/27] ui: correctly reset framebuffer update state after processing dirty regions
Bugzilla: 1527405
RH-Acked-by: Laszlo Ersek <>
RH-Acked-by: Gerd Hoffmann <>
RH-Acked-by: Miroslav Rezanina <>

From: "Daniel P. Berrange" <>

According to the RFB protocol, a client sends one or more framebuffer update
requests to the server. The server can reply with a single framebuffer update
response, that covers all previously received requests. Once the client has
read this update from the server, it may send further framebuffer update
requests to monitor future changes. The client is free to delay sending the
framebuffer update request if it needs to throttle the amount of data it is
reading from the server.

The QEMU VNC server, however, has never correctly handled the framebuffer
update requests. Once QEMU has received an update request, it will continue to
send client updates forever, even if the client hasn't asked for further
updates. This prevents the client from throttling back data it gets from the
server. This change fixes the flawed logic such that after a set of updates are
sent out, QEMU waits for a further update request before sending more data.

Signed-off-by: Daniel P. Berrange <>
Reviewed-by: Darren Kenny <>
Reviewed-by: Marc-André Lureau <>
Signed-off-by: Gerd Hoffmann <>
(cherry picked from commit 728a7ac95484a7ba5e624ccbac4c1326571576b0)
Signed-off-by: Miroslav Rezanina <>
 ui/vnc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ui/vnc.c b/ui/vnc.c
index 7239602..075def1 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -910,7 +910,7 @@ static int vnc_update_client(VncState *vs, int has_dirty)
+    vs->update = VNC_STATE_UPDATE_NONE;
     vs->has_dirty = 0;
     return n;