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Re: [Xen-devel] [PATCH] Xen Guest Kexec

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Subject: Re: [Xen-devel] [PATCH] Xen Guest Kexec
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Fri, 8 Jul 2005 18:35:20 +0100
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As promised, I'm following up with further patches:

This patch:
* http://www.cl.cam.ac.uk/~maw48/kexec/xenguest_kexec_tools.patch
Adds Xen guest kexec support to the kexec tools.  You'll need this to actually 
use the kexec support.

This patch:
* http://www.cl.cam.ac.uk/~maw48/kexec/xenguest_kexec.patch
Is the patch to the Xen distribution, including all my changes *and* the 
"core" kexec changes.  Applying this to a xen-unstable repository allows you 
to build kexec-enabled guest kernels.

This patch:
* http://www.cl.cam.ac.uk/~maw48/kexec/xenguest_kexec_litepatch.patch
Is a reduced version of the above patch, omitting the "core" kexec changes, so 
that it's easier to see what I've added.

My intention is that the changes to the Xen distribution should get merged 
once we've replaced the control message interface in the control tools.  It 
should be there for the 3.0 release.

Eric: do you have any objections to my approach?  I'd ideally like to aim for 
a merge of the tools support at the same time (or before) Xen support arrives 
in mainline Linux.


On Thursday 07 July 2005 18:16, Mark Williamson wrote:
> All,
> I'm posting to the Xen-devel list and the OSDL fastboot list.  There are a
> number of Xen folks who'll want to look at the code.  For the fastboot
> folks, this is mostly intended as an announcement of the port.  Please
> limit your replies to the list(s) that they applies to, thanks :-)
> A number of people have expressed interest in kexec support for Xen guests.
> In particular, it's mainly useful for purposes of implementing an in-guest
> bootloader app and avoiding the need for dom0 to access the guest
> filesystem.
> It's a largish patch, so I stuck it online:
> http://www.cl.cam.ac.uk/~maw48/xenguest_kexec.patch
> Tested on i386.  I suspect it'll have build issues on x86_64 but those
> should be easy to fix - actually the code is probably generic enough to
> work on both.
> You'll also need a modified version of the kexec tools, which I'll post
> details of later.
> Notes on the implementation:
> Kexec in a Xen guest doesn't work like on a real machine.  The guest relies
> on outside assistance to complete the job.  The guest communicates details
> of the kexec to Xend.  Xend extracts the data from the guest's memory image
> and uses it to rebuild the domain with a new kernel, etc.  This approach
> simplifies the changes needed to support kexec and minimises code
> duplication between Linux and the domain builder itself.
> Kexec-ing the whole host is a separate issue, I think it's best addressed
> with a port of kexec to Xen itself.
> Cheers,
> Mark
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