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Re: [Xen-devel] Xen Save File - VM's memory image

To: Amin Firoozshahian <aminf13@xxxxxxxxx>
Subject: Re: [Xen-devel] Xen Save File - VM's memory image
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Tue, 14 Jul 2009 09:56:26 +0100
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At 18:10 +0100 on 13 Jul (1247508644), Amin Firoozshahian wrote:
>   I'm sorry for posting this to the developer's mailing list, but I'm
> almost sure that no one in the user list would be able to help me. I'm
> experimenting with a few VMs and I need to have access to the contents
> of the VMs (physical) memory that is written in the save file. I read
> on the mailing archives that there's no documentation on the save file
> format (right?). I was wondering can anyone help me by pointing me to
> the location in the save file that is the start of VM's memory image
> (e.g. X byes from the beginning/end of the file). The following:
> http://lists.xensource.com/archives/html/xen-devel/2009-06/msg00839.html
>   mentions that someone (Tim?) has developed a set of tools for
> parsing the save file. Would it be possible for me to have access to
> those tools and use them to extract the contents of the VM's memory?

Sorry, the tools referred to there are for parsing Xen's HVM-state
record, not libxc's VM save format.  For that the only documentation is
the code. :(

The memory image is not contiguous in the file, nor even in order; to
get at it you'll have to strip off the xend metadata from the head of
the file and then follow the xc_domain_save code to see what other
fields to throw away until you get to the memory area.  It's saved as
lists of frame numbers followed by their contents.


Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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