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DateThu, 29 Jan 2009 15:19:41 -0800
From"H. Peter Anvin" <>
SubjectRe: RFC: running out of x86 boot loader IDs
Ingo Molnar wrote:
>>
>> - 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?
>
> i think it's prudent to add an extension mechanism, regardless of demand.
> Existing bootloader projects will be content with the IDs they already
> have so they are unlikely to request new ones. Future bootloader projects
> cannot request it because they dont exist yet. So there's no-one to talk
> up.
>

Good point. If so, it probably makes most sense to split pad1 into two
one-byte fields; one for ID and one for version. The bootloader_type
will have to continue to be (ID << 4)+basic_version; we can presumably
add a bootloader_version file which can report a bigger ID.

Either that or we can expose the raw pad1 field as bootloader_exttype
and force any users to be aware of the field splits.

-hpa



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