Re: [Qemu-devel] fw cfg files cross-version migration races

[Daniel P. Berrange]

On Mon, Jun 01, 2015 at 04:10:54PM +0200, Michael S. Tsirkin wrote:
> Hi all,
> At the moment we have devices adding and removing fw cfg file entries.
> One problem is that this makes the contents of fw cfg
> depend on order of device initialization.
> Since the fw cfg file list is not migrated, this means that
> guest will break if it is migrated between qemu versions
> which generate the list diferently, and if migration triggers
> while guest happens to read fw cfg.
> 
> As there are plans to extend the use of fw cfg, I think it's
> important to fix this issue sooner rather than later.
> 
> Ideas:
>       - sort fw cfg files by name before exposing them to guest
>       - keep doing what we did for compat machine types,
>         hope that things don't break too often
> 
> More ideas? Comments? Anyone wants to try implementing this?

Shouldn't we migrate the fw cfg data that the source host generates
originally,  rather than trying to play games make sure the way it
is re-generated on dest doesn't change.

Regards,
Daniel
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