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RE: Building domains as a lesser user (was Re: bootloaders for domain != 0)
> On Fri, 2005-02-04 at 02:30 +0000, Ian Pratt wrote:
> > One fairly simple option is to use Linux as a domU boot loader. Boot
> > with an intrd, mount the specified filesystem, read off
> grub.conf, display a menu over
> > the xencons, kexec the appropriate kernel.
>
> Linux really seems like a very heavy hammer for something like this.
> Even just thinking from a resource perspective, why boot up a whole
> kernel to do nothing more than read an fs and mount another kernel.

I don't buy the resource argument: it takes only a couple of seconds to
boot a xenU kernel to user space, and you're about to be booting another
kernel anyhow.

> Especially as you start thinking about things like modular fs's, etc,
> it's going to be much less clean of a solution and be a significant
> slowdown on your guest boot time.

A few seconds slow down -- nothing compared to what a BIOS normally
adds.

I don't see why the filesystems would particularly need to be modular,
though you might do so for convenience.

> And then, it's yet another kernel to keep updated, etc.

I don't see any reason to keep it up to date. Its running in a protected
environemnt and doesn't have any extra access that the kernel about to
be booted is going to get.
I think this approach will work well.

We already booy all of our *physical* machines using a CDROM containing
a Linux bootloader -- see xenoboot:
http://www.cl.cam.ac.uk/Research/SRG/netos/xeno/xenoboot/

Ian


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Re: Building domains as a lesser user (was Re: bootloaders for domain != 0) [ In reply to ]
Ian Pratt wrote:
>>On Fri, 2005-02-04 at 02:30 +0000, Ian Pratt wrote:
>>
>>>One fairly simple option is to use Linux as a domU boot loader. Boot
>>>with an intrd, mount the specified filesystem, read off
>>
>>grub.conf, display a menu over

Well I don't think it even being grub compatible is necessary. I'd say
it looking a little like lilo, yaboot and the like would do just fine.

What a splendid idea! I think this would be _very_ easy with a very
small script out of initrd? Or _even_ out of rc2.d!?!

read -p 'boot: ' kernel
kexec /boot/$kernel

-apw


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Re: Building domains as a lesser user (was Re: [Xen-devel] bootloaders for domain != 0) [ In reply to ]
On Fri, 2005-02-04 at 10:23 +0000, Andy Whitcroft wrote:
> Ian Pratt wrote:
> >>On Fri, 2005-02-04 at 02:30 +0000, Ian Pratt wrote:
> >>
> >>>One fairly simple option is to use Linux as a domU boot loader. Boot
> >>>with an intrd, mount the specified filesystem, read off
> >>
> >>grub.conf, display a menu over
>
> Well I don't think it even being grub compatible is necessary. I'd say
> it looking a little like lilo, yaboot and the like would do just fine.

I'd argue you want it to look like the "native" boot loader for the
architecture. If it doesn't, then you have to do more special casing to
handling updating the guest's boot loader config. As well as more
special casing of users' brains telling their hands what to type ;-)

Jeremy



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Re: Building domains as a lesser user (was Re: [Xen-devel] bootloaders for domain != 0) [ In reply to ]
> I'd argue you want it to look like the "native" boot loader for the
> architecture. If it doesn't, then you have to do more special casing to
> handling updating the guest's boot loader config. As well as more
> special casing of users' brains telling their hands what to type ;-)

For what i want, any valid bootloader would be fine. So if its as dumb
looking as lilo (yaboot) thats fine with me.

-apw


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