GPT boot loader?

[Marcel Moolenaar]

On May 22, 2007, at 11:58 AM, Craig Boston wrote:

> On Tue, May 22, 2007 at 02:34:02PM -0400, Marcel Moolenaar wrote:
>> GPT is not designed to be a sub-partitioning scheme. It can not be
>> used within a partition. As such, absolute block addresses are the
>> same as relative block addresses. As such, no mistake has been made
>> yet.
>
> Ah, that does make sense.  Does the GPT specification actually say
> absolute block addresses?

No. It actually hints strongly towards relative addressing:

"The EFI firmware produces a logical BLOCK_IO device for each EFI  
Partition
  Entry, El Torito logical device volume, and if no EFI Partition  
Table is
  present any partitions found in the  partition tables.  Logical block
  address zero of the BLOCK_IO device will correspond to the first  
logical
  block of the partition."

...

"EFI supports the nesting of legacy MBR partitions, by allowing any  
legacy
  MBR partition to contain more legacy MBR partitions.  This is  
accomplished
  by supporting the same partition discovery algorithm on every  
logical block
  device.  It should be noted that the GUID Partition Table does not  
allow
  nesting of GUID Partition Table Headers.  Nesting is not needed  
since a
  GUID Partition Table Header can support an arbitrary number of  
partitions
  (the addressability limits of a 64-bit LBA is the limiting factor)."

So: addressing is relative by implication (i.e. by the use of logical  
block
addresses) and the only reason GPT cannot be nested is that it's  
considered
unnessesary. Not because GPT is not to use relative/logical block  
addresses.

>   That would seem to be redundant if the spec
> also forbids its use inside a partition.  I can't seem to find the
> actual documents for GPT anywhere.

GPT is defined in the EFI specification. Look for the EFI specification.
I consider that the authoritative specification.

>> FreeBSD actually creates a GPT with relative addresses, which means
>> that if we allow it to be used to sub-partition partitions, it would
>> not have the same problem as the BSD label.
>
> I suppose we're being nonstandard either way, so I'll keep my fingers
> crossed that this continues to be the case :)

Not is this respect. We still don't allow GPTs to be nested so the
issue is moot :-)

-- 
Marcel Moolenaar
xcllnt at mac.com