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[libvirt] Proposed functionality: API to extract host description from saved state, restore with modified XML

Per subject. Obviously only for use by folks who *really* know what they're doing. :)

I'm looking for the ability to restore a snapshot saved with domain.save(), with disk images pointing at a different location (in my particular use case, pointing at a an empty copy-and-write image backending into a snapshot of the old disk state). Further, as I may run multiple copies of the same host at once (from the same initial state, against different copy-on-write disk images backending into the same read-only store, into different disconnected networks), the UUID as well as the name may need to be changed.

I could just rewrite the header of the saved-state file, but this has a few disadvantages: - To mimic the copy-on-write behavior of the disk images, I would need to copy the entire saved-domain file. I'm trying to minimize the time and disk penalty of snapshot/restore, so this is suboptimal. - My code is dependent on the file format used by the particular backend, and may break when that backend is revved.

Would a patch adding API calls to
 - return the XML description of a saved host, given the name
 - restore a saved host with a different description
be considered welcome?

I presume that to maintain backwards compatibility, the latter would be expected to be exposed to clients via a new call, rather than adding a parameter to virDomainRestore(); in communicating with the drivers, on the other hand, my first instinct would be to add an extra parameter to virDrvDomainRestore.


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