Re: [Bug-xorriso] [bug #46716] Protective MBR partition is not marked as bootable

[Thomas Schmitt]

Hi,

i wrote:
> > I currently try to talk Debian out of nesting partitions,
> > even id the big one is type 0x00.

Alexander E. Patrakov wrote:
> If the discussion is archived somewhere, a pointer to it would be nice to
> have.

I made a lenghty assessment of Debians amd64 and i386 setup at
occasion of this bug report
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=776317#75
(which is about a misunderstanding, actually).

Then i hopped on that topic in debian-cd list like Cato the Elder
did on Carthago. This must have been annoying enough so that
Debian's arm64 ISOs have this layout:

  $ xorriso -indev debian-8.1.0-arm64-netinst.iso -report_system_area plain 
-report_el_torito plain
  ...
  ISO image size/512 : 329728
  ...
  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x00  0x83            0       329728
  MBR partition      :   2   0x00  0xef       329728         2048
  El Torito catalog  : 918  1
  El Torito cat path : /boot.catalog
  El Torito images   :   N  Pltf  B   Emul  Ld_seg  Hdpt  Ldsiz         LBA
  El Torito boot img :   1  UEFI  y   none  0x0000  0x00    768         919
  El Torito img path :   1  /boot/grub/efi.img

Note that partition 2 is outside the ISO, while the El Torito
boot image is a file in the ISO. Content is the same, i assume.

Well, arm64 has not legacy BIOS to struggle with.

Currently it looks like your idea with the duplicate partition
of type 0x00 and boot flag is another one which covers all.
But it is as ugly as isohybrid+GRUB2 for BIOS+EFI as in Debian
amd64 ISOs.


> [instructions for grub-mkrescue on Debian VM]

I will try to make my own grub-mkrescue image before the year
is over. :))


> http://82.193.153.141/minimal.iso

It contains the full orchestra:

  System area summary: MBR protective-msdos-label grub2-mbr cyl-align-off GPT 
APM
  ISO image size/512 : 32852
  Partition offset   : 0
  MBR heads per cyl  : 64
  MBR secs per head  : 32
  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x00  0xee            1        32851
  GPT                :   N  Info
  GPT disk GUID      :      781a13c2a0f79b4ead7fe455e9b7e46c
  GPT entry array    :      20  176  separated
  GPT lba range      :      64  32806  32851
  GPT partition name :   1  4700610070003000
  GPT partname local :   1  Gap0
  GPT partition GUID :   1  781a13c2a0f79b4ead7ce455e9b7e46c
  GPT type GUID      :   1  a2a0d0ebe5b9334487c068b6b72699c7
  GPT partition flags:   1  0x1000000000000001
  GPT start and size :   1  64  272
  GPT partition name :   2  
450046004900200062006f006f007400200070006100720074006900740069006f006e00
  GPT partname local :   2  EFI boot partition
  GPT partition GUID :   2  781a13c2a0f79b4ead7de455e9b7e46c
  GPT type GUID      :   2  28732ac11ff8d211ba4b00a0c93ec93b
  GPT partition flags:   2  0x1000000000000001
  GPT start and size :   2  336  5760
  GPT partition path :   2  /efi.img
  GPT partition name :   3  4700610070003100
  GPT partname local :   3  Gap1
  GPT partition GUID :   3  781a13c2a0f79b4ead7ee455e9b7e46c
  GPT type GUID      :   3  a2a0d0ebe5b9334487c068b6b72699c7
  GPT partition flags:   3  0x1000000000000001
  GPT start and size :   3  6096  26708
  APM                :   N  Info
  APM block size     :      2048
  APM gap fillers    :      2
  APM partition name :   1  Gap0
  APM partition type :   1  ISO9660_data
  APM start and size :   1  16  1508
  APM partition name :   2  HFSPLUS_Hybrid
  APM partition type :   2  Apple_HFS
  APM start and size :   2  1524  6527
  APM partition name :   3  Gap1
  APM partition type :   3  ISO9660_data
  APM start and size :   3  8051  162
  El Torito catalog  : 1669  1
  El Torito cat path : /boot.catalog
  El Torito images   :   N  Pltf  B   Emul  Ld_seg  Hdpt  Ldsiz         LBA
  El Torito boot img :   1  BIOS  y   none  0x0000  0x00      4        7916
  El Torito boot img :   2  UEFI  y   none  0x0000  0x00   5760          84
  El Torito img path :   1  /boot/grub/i386-pc/eltorito.img
  El Torito img opts :   1  boot-info-table grub2-boot-info
  El Torito img path :   2  /efi.img

(Note how neatly Vladimir and i avoided any partition nesting
 when planning this layout.
 Lengthy explanation of the report format: 
   xorriso -report_system_area help -report_el_torito help | less
)

Achieved by these -as mkisofs options:

  $ xorriso -indev minimal.iso -report_system_area as_mkisofs
  ...
  --grub2-mbr ...local.file...
  --protective-msdos-label
  -apm-block-size 2048
  -hfsplus
  -efi-boot-part --efi-boot-image
  -c '/boot.catalog'
  -b '/boot/grub/i386-pc/eltorito.img'
  -no-emul-boot
  -boot-load-size 4
  -boot-info-table
  --grub2-boot-info
  -eltorito-alt-boot
  -e '/efi.img'
  -no-emul-boot
  ...


> By the way, I have also created an ISO with a hybrid MBR by treating the
> original minimal.iso with gdisk. The iso is available at
> http://82.193.153.141/minimal-hybrid.iso

I assume that its MBR lets any decent EFI ignore the GPT:

  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x00  0xee            1           63
  MBR partition      :   2   0x80  0x07           64          272
  MBR partition      :   3   0x00  0xef          336         5760
  MBR partition      :   4   0x00  0x07         6096        26708
  MBR partition path :   3  /efi.img

Isn't 0xee a misnomer now that you decided for MBR ?
Actually one could save one partition slot by leaving the first
few blocks unclaimed or by extending partion 2 to block 1.

  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x80  0x07            1          335
  MBR partition      :   2   0x00  0xef          336         5760
  MBR partition      :   3   0x00  0x07         6096        26708


Nevertheless, your overlapping layout would have the appeal of
giving a mountable partition:

  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x80  0x00            0        32804
  MBR partition      :   2   0x00  0xef          336         5760

It would travel on the ticket that EFI shall ignore MBR partition
type 0x00. Ugly, but well tested by Debian amd64 isohybrid+GRUB2.


My personal favorite would be what Debian arm64 does, plus a
boot flag:

  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x80  0x83            0        32804
  MBR partition      :   2   0x00  0xef        32804         5760

To be produced by these options

  -append_partition 2 0xef ...local.path.../efi.img
  -G ...local.file.with.a.few.binary.zeros...
  -c '/boot.catalog'
  -e '/efi.img'
  -no-emul-boot

Debian's amd64 EFI system partition is smaller than yours.
It contains just enough GRUB2 to find the GRUB2 installation
inside the ISO filesystem. Menus and other stuff are only in
that ISO directory.


Have a nice day :)

Thomas