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

From: Thomas Schmitt
Subject: Re: [bug #46716] Protective MBR partition is not marked as bootable
Date: Sat, 19 Dec 2015 17:55:20 +0100


[taking Alexander out of Cc: as he probably gets the mails
 from the lists twice, as i do]

I currently only have some mockup ISO from HFS+ experiments
with Vladimir. 

When i replay its xorriso -as mkisofs boot related options

  --grub2-mbr ...some.file...
  -apm-block-size 512
  -c '/BOOT.cat'
  -b '/img1'
  -boot-load-size 4

i get an MBR partition without boot flag.

The immediate reason is that the wish to produce HFS+ lets libisofs
think that there will be a GPT.
In my special case there emerges only MBR partition table and APM.
But i am not sure that this case is realistic.

The criterion for omitting the bootability flag at the
found occasion is:

  There is an EFI boot partition
  or ( there will be HFS+ but not CHRP partitioning )
  or there are already GPT partitions planned

About the middle part i am unsure why it exists.
The other two correspond somewhat with Andrei's expectations,
i'd say. I'll have to research whether Vladimir explicitely
prescribed them to me.

Whatever, if i leave out option -hfsplus, then i get a protective
MBR partition with boot flag:

  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x80  0xcd            1          227

>From what Alexander reports, i assume that his xorriso -as mkisofs
options included

  --efi-boot efi.img
  -efi-boot-part --efi-boot-image

They are supposed to prevent the boot flag in MBR (because of the
first of the above criteria).


So the only unintentional reason for no boot flag might be the
fact that HFS+ deliberately prevents it, even if no EFI System
Partition and no GPT is to be produced.
Even if this ctriterion is too wide, there was quite probably
some special case for which it was written into the code.
(... if i only could remember ... the bzr history looks like
 it was intended from the beginnings of HFS+ support ...)

Have a nice day :)


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