Re: [Xen-devel] VM checkpoint image format

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 21/12/2013 16:31, Prateek Sharma wrote:
> Hello all,
>     Is the VM-save image format specified anywhere? (the file written
> to by xc_domain_save). I am looking for what fields are saved in what
> order.
>     Or is the xc_domain_save function itself the specification? Can I
> change the order of fields saved (thus changing the on-disk image
> format) and expect no breakages? Ofcourse, I will need to change the
> xc_domain_restore function as well.
>
> Thanks!
> --Prateek

There is no documentation that I am aware of, other than the code
itself, and the code is a rats nest.  The format itself is quite lacking
in terms of extensibility, and makes some assumptions which are not
actually accurate.

In my copious free time (of which I have none), or when XenServer
decided that it actually wants migration which works in combination with
ballooning (or any of the other more interesting memory modes), I have a
plan to make a "migration protocol v2" which shall be formally specified
in a document, and have ample room for forward extensibility in a
backward compatible manner.


As for changing the order of things.  So long as your xc_domain_save()
and xc_domain_restore() have similar expectations of what order to
put/find chunks of the stream, it should work fine.  It would help if
you described what changes you wish to make.  We might be able to point
you at the correct area.

~Andrew

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