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

[Alexander E. Patrakov]

29.12.2015 21:05, Thomas Schmitt пишет:
> 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 ?

Assuming that a layout is chosen that has a protective MBR partition of 
type 0xee and thus needs a dummy bootable MBR partition, I would prefer 
it to cover a single block at the start of the iso. But if a simpler 
MBR-only layout works and doesn't need dummy partitions, then I would 
prefer it even more.

> 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.

This looks good.

> (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.

So here we agree on the set of valid options.

> > 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.

Right.

> 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.)

Thanks for the suggestion, but I will be able to retest only tomorrow.

> > 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 ?

Yes! And it shows it despite the fact that there is no bootable partition!

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

Right.

> -----------------------------------------------------------------
> 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]),

This was already tested and works.

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

Not sure if I understand this variant correctly, a report from xorriso 
would be welcome.

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

This would work, too.

> 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.

Good. But I'd rather wait for Mac results before approving the mbr_only 
layout.

--
Alexander E. Patrakov