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Re: [Xen-devel] Re: PXE boot

To: Ruediger Berlich <ruediger.berlich@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: PXE boot
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>
Date: Thu, 29 Jul 2004 08:32:53 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxxx, Ian.Pratt@xxxxxxxxxxxx
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> Hi there, 
> > Xen currently doesn't support booting domains via PXE, though at 
> > some point someone talked about adding it. Basically, the domain 
> > builder would do the PXE request and tftp the kernel image that 
> > would be place in the domain. 
> >  
> > I'm sure you could get the domains booting sans PXE without too 
> > much hassle anyhow. 
> I would assume that it would probably be sufficient to modify the  
> domain builder in a way that, upon request, it executes a script 
> (kind of like a constructor) before the domain starts up. One could do  
> things like setting up a disk image with all needed data (like the kernel 
> image) in that. As everything is physically handled in domain0, this could 
> easily replace  the PXE  boot. And one could of course do many other cool 
> things in such a constructor (and destructor type) script. Or maybe  
> I'm wrong. 

The domain's kernel image is placed in memory by the domain
builder, so doesn't need to come off the domain's virtual disk.

PXE is basically a combination of DHCP and tftp.

We could have the domain builder issue a DHCP request using the
domain it's building's MAC address, then use tftp to fetch the
kernel image into a temporary file that the domain builder can
then use. 

Adding support to xend to do this shouldn't be hard. The only
slightly non trivial bit is sending a DHCP request using someone
else's MAC -- rather than hacking dhclient it's probably easiest
to hand craft something one-shot as you don't need a daemon
(presumably you can rely on the server giving the same address to
the same MAC if asked in quick succession)


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