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Re: [multiboot] command-line format

From: Grégoire Sutre
Subject: Re: [multiboot] command-line format
Date: Sun, 17 Jan 2010 19:02:16 +0100
User-agent: Thunderbird (X11/20091027)

Hi Robert,

Thanks for your detailed explanation, it was really helpful to me. I understand that for compatibility with some platforms, GRUB must provide a way to specify two potentially different file parameters:

(a) the GRUB path to the booted file; this path does not appear in the multiboot command-line. (b) the path that shall be passed to the booted file; this path (if any) is the first argument in the multiboot command-line.

However, my first post in this thread was more about the multiboot specification itself. In light of your explanations, I would re-phrase my suggestion as follows: in the multiboot specification, require that the first argument of the MB command-line be a path to the booted file *in a notation that is specific to the booted kernel*. Or, if this is too constraining or too confusing, simply ask that the first argument is an informative string that does not contain kernel options (i.e. it can safely be skipped). This way, the specification would be closer to the reference implementation (GRUB Legacy), and, more importantly, to what multiboot-compliant kernels already *assume* about the format of the command-line (NetBSD, OpenSolaris, Xen, others?).

For GRUB 2, this could be implemented by a multiboot command that, by default, behaves as GRUB Legacy, but also offers a way to modify the implicit first argument of the multiboot command-line. Something like:

multiboot $path[;$ospath] ...

(a) $path is the GRUB path to the booted file.
(b) $ospath is the path that shall be passed to the booted file.

By default, if there is no ';' in the first argument, $ospath is set to the value that GRUB Legacy would have used. Maybe a GRUB shell variable `multiboot_ospath' would be better than this ';' marker.

This way, we keep the extra flexibility of having different paths, but we also:

- keep backward compatibility with GRUB Legacy: kernels can still assume that the first argument of the multiboot command-line is not a kernel option. - don't force users to repeat the path for kernels that are happy with the way GRUB Legacy worked (all of them except OpenSolaris?). I agree that this point is of no concern to most users, but in some cases grub-mkconfig does not work (e.g. grub-mkconfig does not support --root-directory at the moment), and some users prefer the flexibility of the command line anyway.


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