RE: [Xen-devel] boot loaders for domain != 0

[Jeremy Katz <katzj@xxxxxxxxxx>]

On Thu, 2005-02-03 at 14:28 +0000, Ian Pratt wrote:
> > I know that one doesn't need a bootloader for domains != 0.  
> > However, I 
> > have a desire to configure a system this way (to make it a 
> > good facimily 
> > of a bare metal system) and am wondering what if any support for boot 
> > loaders there might be?  I presume that there is no BIOS 
> > available when 
> > running on 'xen virtualised hardware'.  Is there anything 
> > even similar 
> > available or planned.  How hard might it be?
> 
> I think you could get most of this functionality by allowing the
> location of the kernel to be specified as a file within one of the
> guests virtual disks (assuming dom0 knows how to mount the root file
> system).

Except that you really want to be able to update from within the guest
what kernel is used instead of having to specify it in dom0.  That then
makes the guest almost completely independent on questions of what
software runs inside it.

> We could also access a config file within the guest's virtual disk that
> could be used to override a subset of the config parameters (e.g.
> command line, kernel image name etc).

Parsing a grub.conf is easy enough that you're probably just as well off
reading it from dom0 and parsing it to determine what the right thing to
boot is.  You can even do it without mounting by using something like
libext2fs.  Going really all out would then make it so that when you
first started a guest domain, you'd be presented with a menu to pick
what you want (based on the boot loader config), just like you would
with a normal machine.  

> Volunteers? :-)

It's something that I'll probably end up doing eventually if no one
beats me to it.  But I need to get further on the device infrastructure
stuff first.

Jeremy



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