Re: save image file format? and [RFC] tmem save/restore/migrate

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

Tim Deegan wrote:

> At 13:02 +0100 on 18 Jun (1245330161), Stefano Stabellini wrote:
>> At least in theory is certainly feasible: just a matter or registering
>> another savevm function for a record called "cpu" or "vcpu", that would
>> take care of saving the guest memory using xc_domain_save.
> 
> Yuck.  You still need to add a bunch of metadata from xend that qemu
> doesn't know about, so you'll have to wrap the qemu output in another
> file format already.  Wrapping the memory image inside qemu's image is
> just layering for its own sake.  (Also, using qemu to save a PV guests 
> would be pretty wierd).


Most (but unfortunately not all) the information saved by xend are qemu
command line options or easy to get from them.
Certainly being backward compatible is going to be harder this way than
involving xend.

 
>> The qemu people are also maintaing save record compatibility now, so we
>> are safe from that perspective.
> 
> Yes, but their code-defines-format model is rubbish.  I've written a
> couple of tools that parse HVM save file info based on the Xen public
> headers; doing the same for a qemu-style implicit format is a PITA.
> 

We can always write an rfc that documents the format and request them to
keep it up to date.
We can also reuse exiting loadvm qemu code to write tools, even though
it wouldn't be as elegant as using xen public headers.