[Bug 1062737] Re: hybrid images do not include a valid GPT

[Steve Langasek]

I've built a test image now using the cherry-picked patch from 1.2.5,
and confirmed that the -partition_offset option now happily coexists
with -isohybrid-gpt-basdat in all of my testing (USB boot on real UEFI
hardware; USB and CD boot in BIOS VM; USB boot in UEFI VM).  So that
seems to be a suitable fix.

However, as the resultant image still appears to not have a valid MBR
partition table, there doesn't seem to be any advantage to adding this
option back to our builds for 12.10.  So I think we'll leave it as is
with -partition_offset 16 disabled for now.

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https://bugs.launchpad.net/bugs/1062737

Title:
  hybrid images do not include a valid GPT

Status in Ubuntu CD image build software:
  Fix Released
Status in “libisofs” package in Ubuntu:
  Triaged

Bug description:
  The insyde UEFI firmware implementation does not see the GPT on the
  hybrid images generated on nusakan (e.g., the 12.10 beta2 image).
  This appears to be consistent with what both gdisk and parted show:

  $ gdisk -l ~/devel/iso/ubuntu-12.10-beta2-desktop-amd64.iso 
  GPT fdisk (gdisk) version 0.8.5

  Partition table scan:
    MBR: MBR only
    BSD: not present
    APM: not present
    GPT: not present

  
  ***************************************************************
  Found invalid GPT and valid MBR; converting MBR to GPT format.
  ***************************************************************

  Disk /home/vorlon/devel/iso/ubuntu-12.10-beta2-desktop-amd64.iso: 1548288 sectors, 756.0 MiB
  Logical sector size: 512 bytes
  Disk identifier (GUID): 1ADDF8C9-5CE1-41A4-9124-2CC80EED991F
  Partition table holds up to 128 entries
  First usable sector is 34, last usable sector is 1548254
  Partitions will be aligned on 2048-sector boundaries
  Total free space is 1548221 sectors (756.0 MiB)

  Number  Start (sector)    End (sector)  Size       Code  Name
  $

  Removing the -partition_offset 16 option from the xorriso commandline
  is sufficient to generate an image with a recognizable partition
  table; but I imagine this causes other problems for hybrid systems.

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