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Re: passing options to grub in xen,openfirmware and efi

From: Olaf Hering
Subject: Re: passing options to grub in xen,openfirmware and efi
Date: Wed, 29 Apr 2015 18:49:21 +0200
User-agent: Mutt/1.5.22.rev6346 (2013-10-29)

On Wed, Apr 29, Vladimir 'phcoder' Serbinenko wrote:

> On Apr 29, 2015 6:28 PM, "Olaf Hering" <address@hidden> wrote:
> >
> > On Wed, Apr 29, Vladimir 'phcoder' Serbinenko wrote:
> >
> > > There is a standard where to put it. See xen docs
> >
> > Yes, its like that:
> > kernel="/usr/whatever/distro/grub.xen"
> > extra="opt1=val opt2=val"
> >
> That's not what I meant. There is a standard on where to find files inside the
> domU.

There are likely ways to find out where grub was loaded from even on a
PC, and use that as initial root=. In a PV guest no such thing exists
because itself grub is the firmware. In OF I can imaging that it might
be useful to point grub right away to some other device than listed in

> > And grub2 does not grab the cmdline provided via extra=. I think that
> > providing root=xen/xvdb is the right way to control grub inside the
> > domU.
> > In anycase, what the OF does today in its init code is valid and should
> > stay.
> Mixing up namespaces is certainly not valid. This will lead to both intended
> misuses like changing variables that shouldn't be and unintentional when e.g.
> root=/dev/xvda2 meant for Linux will sneak into grub breaking stuff

Since the kernel= is grub and the stuff in cmdline is obviously meant
for that very kernel (grub), it can have no meaning for an OS that
possibly loaded later. It does not even know about that string.


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