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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