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Re: [Qemu-devel] [Qemu-stable] [PATCH v2 for 2.7] ui: fix refresh of VNC


From: Peter Lieven
Subject: Re: [Qemu-devel] [Qemu-stable] [PATCH v2 for 2.7] ui: fix refresh of VNC server surface
Date: Thu, 25 Aug 2016 09:15:52 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

Am 24.08.2016 um 17:49 schrieb Daniel P. Berrange:
On Wed, Aug 24, 2016 at 04:46:31PM +0100, Peter Maydell wrote:
On 23 August 2016 at 07:50, Peter Lieven <address@hidden> wrote:
Am 16.08.2016 um 18:30 schrieb Daniel P. Berrange:
In previous commit

    commit c7628bff4138ce906a3620d12e0820c1cf6c140d
    Author: Gerd Hoffmann <address@hidden>
    Date:   Fri Oct 30 12:10:09 2015 +0100

      vnc: only alloc server surface with clients connected

the VNC server was changed so that the 'vd->server' pixman
image was only allocated when a client is connected.

Since then if a client disconnects and then reconnects to
the VNC server all they will see is a black screen until
they do something that triggers a refresh. On a graphical
desktop this is not often noticed since there's many things
going on which cause a refresh. On a plain text console it
is really obvious since nothing refreshes frequently.

The problem is that the VNC server didn't update the guest
dirty bitmap, so still believes its server image is in sync
with the guest contents.

To fix this we must explicitly mark the entire guest desktop
as dirty after re-creating the server surface. Move this
logic into vnc_update_server_surface() so it is guaranteed
to be call in all code paths that re-create the surface
instead of only in vnc_dpy_switch()

Signed-off-by: Daniel P. Berrange <address@hidden>

I noticed that these patches is as well not in master yet and therefore
not included in the 2.7.0-rc4 tagged yesterday.
Dan, Gerd -- we're going to need an rc5 anyway -- can you
comment on whether this patch is "should be in rc5"
material? (If it is I can commit it to master directly.)
I think it should be, as the VNC server is pretty unusable when it does
not refresh the screen when you connect, but I'll let Gerd decide in case
there's some implication in my patch that I've mis-understood.

Hi Daniel,

I have had a look at the code and currently I do not understand why you
ran into a blank screen. The server surface is not created if there is no
client connected, this is correct. But the dirty bitmap for the server
exists even if there is no client connected. So the status of the dirty bitmap
should be the same with or without your patch.

Can you tell what exactly you tried out to reproduce a potential issue?

Thanks,
Peter



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