Re: [Xen-devel] [PATCHv1 0/5] tools: rework VM Generation ID

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-05-21 at 14:21 +0100, David Vrabel wrote:
> This series reworks the VM Generation ID to a) conform to the
> published spec from Microsoft; b) simplify the save/restore code; and
> c) extend the libxl API to allow toolstacks to use this feature.
> 
> The VM Generation ID must be regenerated with a new random ID after
> certain VM operations. For xl, a new ID is required when restoring
> from a saved image (but not after a migration, reboot, pause/unpause).

Does reboot include shutdown and recreate? i.e. if I do
 xl shutdown domain
 xl create domain.cfg

what should happen?

If we have to preserve then that is going to be problematic for xl,
since:
 xl create domain.cfg
 xl save domain saved
 xl restore saved # now the genid has changed
 xl shutdown domain
 xl cr domain.cfg

has nowhere to store the new genid, even if domain.cfg were to contain
the original one.

> Can someone advise on the best way to implement this in xl?

Would a new bool field in libxl_domain_restore_params to indicate
whether to preserve or regenerate the ID be sufficient? xl would set it
appropriately when restoring or on migrate receive.

Hrm, that doesn't work for reboot does it.

> We could put a vm-generation-id variable in the domain configuration
> file.  This would end up in the saved configuration file and would be
> reused or regenerated on restore depending on whether the domain was
> migrated or restored from a file.

Do you really mean the domain configuration file or did you just mean
libxl_domain_config? (which one I think you mean depends on the answer
to the shutdown/create question I think).

If libxl_domain_config then Wei's work to preserve domain config on
save/restore/migrate etc would then cause the right thing to happen.

Ian.

> 
> You can download the spec from:
> 
>   http://www.microsoft.com/en-us/download/details.aspx?id=30707
> 
> David
> 



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