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Re: Replacing the legacy 'map' command

From: Javier Martín
Subject: Re: Replacing the legacy 'map' command
Date: Wed, 28 May 2008 15:17:30 +0200

> The cooperation between modules is not hard, but I think
> map -first (hdx) will be more useful. Such command just swaps hd0 and hdx
> drives. This also covers the scenarios when we chainload something else
> than first sector of given partition.
> And maybe we can also consider following syntax:
> map -pos (hd2) (hd0) (hd4)
> with meaning:
>   hd0->hd1,
>   hd1->nothing
>   hd2->hd0,
>   hd3 not touch,
>   hd4->hd2
> I.e. positional syntax, first argument is mapped to (hd0), second to (hd1),
>   and so on.
> This syntax will be sufficient most times and writing
>   chainloader --automap (hd1,0)+1
> is same as writing
>   map -first (hd1)
>   chainloader (hd1,0)+1
> or
>   setting grub root to (hd1,0)
>   map -root
>   chainloader +1
> --
> Tomas Ebenlendr

Well, such "additional" UIs will be useful, and there seems to be some
consensus on how this should be done:
   1.- There should be a new command called somethink like "drivemap"
and based on a new module that would provide the drive mapping
   2.- This module would be available in x86/PC (and, if it is ever
split from it, AMD64/PC), and would work by saving the user requested
mappings and installing a pre-boot GRUB routine.
   3.- Such a routine would, before the execution of grub_X_real_boot,
install the appropate ISRs (which are mostly available in GRUB Legacy
code) to make the mappings effective, no matter what the OS loader is
- chain, multiboot, etc.

Therefore, if there are no objections to this plan, I can start the
implementation (when I finish my exams, of course u_u). I think I will
initially place the ISR installation code in
grub_chainloader_real_boot in order to have a working version right
away, then move it away into its own function and, however the way,
"register" it with the boot routines so that it is executed as
mentioned above. Other modules/commands would be later modified to add
drivemap-related functionality. Is there any site/document (apart from
the sources themselves) in which I can learn more about the internals
of GRUB2 and, specifically, the "boot" command sequence?.


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