Re: [Qemu-devel] [libvirt] Bug: vnc + websocket = websocket autoport not working right at live migration

[Martin Kletzander]

On Tue, Jun 23, 2015 at 02:13:21PM +0200, Piotr Rybicki wrote:
> Hello.
>
> Problem description:
>
> When i start qemu via libvirt with vnc websocket defined, it is not
> possible to live migrate to host where other qemu process is running
> with the same display id.
>
> migration error is:
>
> error: internal error: early end of file from monitor: possible problem:
>            [1] => 2015-06-23T11:54:25.590506Z qemu-system-x86_64: -vnc 
> 0.0.0.0:1,websocket=5700,password: Failed to start VNC server on `(null)': Failed 
> to bind socket: Address already in use
>
> (please note vnc display id=1 and websocket=5700 - where it should be 5701)
>
> in libvirt's xml i have:
> (...)
>    <graphics type='vnc' port='-1' autoport='yes' websocket='-1'
> listen='0.0.0.0' passwd='xxx'>
>      <listen type='address' address='0.0.0.0'/>
>    </graphics>
> (...)
>
> for first and only qemu process on host, this creates qemu commandline:
> (...) -vnc 0.0.0.0:0,websocket=5700,password (...)
>
> for second qemu process on the same host:
> (...)  -vnc 0.0.0.0:1,websocket=5701,password (...)
>
> There is no problem with migration, when there is no websocket
> configuration.
>
> Solution:
>
> I believe, to solve this problem, libvirt has to omit websocket port
> definition in commandline string ('websocket=5700' => 'websocket')
> when autoport is defined in domain xml definition.

Well, either that or increasing the websocket number as well.  And
that port should be auto-allocated so in case there is something
listening on port 5701 it can select 5702.  That would be even more
error-proof and libvirt would retain full control of qemu (we do that
so that in case the 'websocket = display + 5700' default gets changed,
we still know all the details we set up).

> from man qemu:
>     -vnc display[,option[,option[,...]]]
> (...)
>          websocket
>               Opens an additional TCP listening port dedicated to VNC
> Websocket connections.  By definition the Websocket port is
>               5700+display. If host is specified connections will
> only be allowed from this host.  As an alternative the Websocket port
>               could be specified by using "websocket"=port.  TLS
> encryption for the Websocket connection is supported if the required
>               certificates are specified with the VNC option x509.
>
> So if I understand it right, not specifying websocket port means
> 5700+display id, and display id is given via commandline and
> increments just fine.
>
> Can anyone confirm this? Or perhaps there is some misconfiguration in
> my xml domain definition?

I believe this is a bug in libvirt.  Would you mind creating a bug in
bugzilla for this issue so we can properly track the issue?

Thanks,
Martin

> Best regards
> Piotr Rybicki
>
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