[Spice-devel] Spice console pixelated noise on display changes

[Christophe Fergeau]

Hey,

On Wed, Jul 11, 2018 at 10:45:08AM +0200, Mitja Mihelič wrote:
> Answering the question for posterity.
> We found a temporary solution to the described problem.
> We had an oVirt development cluster with a working SPICE console. By
> comparing packages we have established the differences between working and
> not working SPICE setup. We have isolated the spice-server package.
> The installed version was spice-server-0.14.0-2.el7_5.3.x86_64
> We downgraded the package to spice-server-0.12.8-2.el7.1.x86_64 and rebooted
> the nodes in sequence.
> Now the SPICE console works again.

Hmm so this is an interesting report. This indicates a regression
between 0.14.0 and 0.12.8, which we want to avoid. I was able to
reproduce without ovirt on a fedora 28 host/guest/client, and to bisect
it to spice-server commit f401eb07 "dcc: Rewrite dcc_image_compress".

This commit introduced a behaviour change, where in some cases images
which were previously compressed with QUIC would be uncompressed. These
uncompressed images have an image stride which is bigger than the image
width, and spice-html5 does not seem to be handling image strides at
all, giving this pixelated look. So in the end, it's a spice-html5 bug,
but it's good there was this bug, as this pointed out a spice-server
regression ;)

I think you should be able to avoid the problem if you manage to force
the compression to quic
(<graphics> <image compression='quic'/> </graphics> in your VM XML).
This is hopefully possible with a ovirt hook (?)

Christophe
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