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
[EMAIL PROTECTED]
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