Re: RFC: running out of x86 boot loader IDs

From: Mikael Pettersson
Date: Thu Jan 29 2009 - 19:33:53 EST


H. Peter Anvin writes:
> The 4-bit values used to hold x86 boot loader IDs are near exhaustion.
> As a result, I'm proposing an extension protocol and will implement it
> in time for the next merge window unless there are objections.
>
> The proposal will be as follows:
>
> - The boot loader IDs (type_of_loader >> 4) E and F will be reserved:
>
> E - extended IDs
> F - special uses
>
> F is consistent with the current use of FF for "unknown".
>
> - If the boot loader ID is E, the current pad1 field at 0x226 is
> repurposed as an extended loader ID. The reason to use the pad1 field
> is that it is present in all headers since version 2.02. The boot
> loader ID will simply be: ((extended ID + 0x10) << 4) + (version), where
> (version) as before is (type_of_loader & 15). This is the value which
> will be reported in /proc/sys/kernel/bootloader_type.
>
> The biggest question is probably: is there a need/desire for an extended
> version field, or is four bits enough for existing bootloader needs?

Why do we need a boot loader id at all? The purpose of a boot loader,
whatever it may be, is to load the kernel according to certain protocols.
Once that's done, why would the kernel care who/what loaded it?
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