Re: RFC: running out of x86 boot loader IDs

[H. Peter Anvin]

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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