[bug-fdisk] A bit further upgrade

[Toshikazu Aiyama, Ph.D.]

Thank you for your recent upgrade to start the first usable partition from 
sector 2048.  I do not know how you got this magic number, but Windows use it, 
and it also is the suggestion by GPT developer: Rod Smith.

The following suggestion is based on util-linux-ng 2.17.2

Main reason for reserving 2047 sectors at the start is GPT conscious: PMBR & 
Primary Partition Table(PPT), I believe.  If you're GPT conscious, why not to 
be conscious about Backup Partition Table(BPT).

Currently default GPT entry array size is 80h bytes.  Since one sector is 200h 
bytes, one sector can hold 4 entries.  According to the specification by GPT, 
up to 128 entries are allowed; thus we need one sector for PTHDR, and 32 
sectors for partition entry array in BPT at minimum.
                                 Minimum  Reserved(Actual)
   PMBR + PPT + Entries array:   1+1+32   2047
   PPT + Entries array:          1+32        1

I am aware of linux limitation of up to 16 partitions per HDD due to Linux 
Device List.

Your current implementation reserves only 1 sector for BPT, but clearly it is 
not enough.


Toshi Aiyama

A boot selector developer