Re: Test Proposal for [bug #46716] Protective MBR partition is not marked as bootable

[Thomas Schmitt]

Hi,

do i understand it right that you decided for the dummy MBR partition
that covers a single block at the start of the ISO ?

If you confirm, i will replace the two macros by a single option
which you can add to your grub-mkrescue run.

How about this:

--protective-msdos-bootflag
    If --protective-msdos-label or --grub2-mbr are given, make sure
    that one of the MBR partitions bears the "bootable/active" flag.
    If that flag is missing then apply it to the first partition
    which is not of type 0xee or 0xef. If no such partition exists,
    then create a dummy partition of type 0x00 which covers only the
    first block of the ISO image.

(An MBR partition which includes block 0 can be neither a
 0xee nor a 0xef. So if there is one, it will get the bootflag
 and no 0x00 partition will get appended.
 No partition overlapping can be added.)

If a --grub2-mjg-layout option emerges, then the effect of
--protective-msdos-bootflag will be extended to that one, too.


The sketching of a comprehensive language for describing
boot sectors and partitions will last a bit longer, i fear.


--------------------------------------------------------------------
Now for alternative layouts:

Alexander E. Patrakov wrote:
> 1. "vanilla": with the modified system_area.c, but with no CPPFLAGS
> 2. "no-boot-dummy": with -DLibisofs_mjg_boot_for_grub2
> 3. "rich": with -DLibisofs_mjg_boot_for_grub2
>    -DLibisofs_protective_msdos_plus_boot_dummY -DLibisofs_pmpbd_on_lba0
> ...
> A. "plain": grub-mkrescue -o minimal-plain.iso minimal
> B. "default": grub-mkrescue -o minimal-default.iso minimal
>     --xorriso=/.../grub-mkrescue-sed.sh
> C: "mjg-p2": MKRESCUE_SED_MODE=mjg MKRESCUE_SED_PARTNO=2 ...
> D: "mbr-only": MKRESCUE_SED_MODE=mbr_only MKRESCUE_SED_PROTECTIVE=no

> All combinations except 1B and 1C are, based on your prior emails, valid,

At least mode "mjg" yields the desired result only with 2 and 3.


> 1A, 1D, 2A: not recognized by the motherboard at all.
> no MBR partitions are marked as bootable on these iso images.

1A and 2A are the reason why this thread exists. They lack of
a non-0xee-0xef partition which one could mark bootable.
   
1D has no boot flag because MKRESCUE_SED_PROTECTIVE=no. You may
trade bootflag for mountable ISO partition by MKRESCUE_SED_PROTECTIVE=yes.
(I will ponder whether boot flag can be enabled by --grub2-mbr
 if some non-0xee-0xef partition is at hand.)
 

> Note: I have also applied Andrei's patch that replaces the boot code in the
> FAT filesystem.
> ...
> 2B: prints "this is not a bootable disk" message that is embedded
> in the new boot code.

You see a string from the EFI partition 0xef in your old BIOS ?

2B lacks boot flag because 0xef is the only MBR partition.


-----------------------------------------------------------------
My conclusions:

Andrei's proposal to have an "mjg" layout (MBR+GPT+APM) works so far,
if it gets augmented by an additional MBR partition which bears a
boot flag.
This may be

- a dummy partition (program variant 3[AB]),

- or a (pseudo-)protective partition (program variant 2C with EFI
  partition as MBR partition 2)

- or a partition which makes the ISO mountable (program 2C with
  MKRESCUE_SED_PROTECTIVE=no).

My proposal "mbr_only" works too (so far), if boot flag is present

- because the program changes for "mjg" included the desire for
  a bootflag (program variant [23]D),

- or because MKRESCUE_SED_PROTECTIVE=yes are in effect (programs
  [1-3]D).

The new proposed option --protective-msdos-bootflag will enforce
the presence of a boot flag if the system area settings indicate 
a GRUB2 MBR.

----------------------------------------------------------------

Both layout proposals still suffer from the fact that the file
efi.img is inside the ISO but also must be appended to its end.

I am now working on implementing an alternative boot image
source which would make file /efi.img in the ISO obsolete.
Current plan:

  -e --interval:appended_partition_2:all::

will point El Torito to the appended MBR partition 2 after the
end of the ISO.
It had a first SIGSEGV and intermediate success. But "mjg" still
lacks its GPT ... will have to look where it got lost ...


Have a nice day :)

Thomas