Re: [Xen-devel] Xen 4.3 development update RC2 imminent

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-05-20 at 11:51 +0100, Wei Liu wrote:
> On Mon, May 20, 2013 at 11:33:23AM +0100, George Dunlap wrote:
> [...]
> > == Open bugs ==
> > 
> > * mac address changes on reboot if not specified in config file
> >   owner: ??
> > 
> 
> I think this is a known issue as xl doesn't update config to stored
> config file.

I think this is only partially related to that. The issue is that if you
don't give a mac address in the config then one is generated randomly
(but this isn't stored in the configuration file). When you migrate a
fresh new MAC address is generated on the destination.

> It also affects things like updating domain name then do migration /
> reboot etc.
> 
> It might be fixed in a straight-forward manner by having stored config
> file update every time domain live config is updated. But I'm not sure.
> 
> I might have a look at this when I have time.

IMHO the right answer is to not send the config file but instead to send
the actual state of the domain, by reconstituting a libxl_domain_config
from the current running state (e.g. using libxl_device_nic_list to make
the list of NICs), pickling that (e.g. as JSON) and unpickling on the
other end.

This is obviously not 4.3 material though.

I'm not sure what a good solution would be for 4.3. There might be scope
for something nasty like propagating the random seed via a hack in the
config file (i.e. append to the saved version "__xl_internal_random_seed
= 42") or just a list of mac addresses to be used. None of the options I
can think of seem terribly desirable :-(

Ian


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