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Re: arm64 and isohybrid


Steve McIntyre wrote:
> >  partition 2 seems broken and I can't mount it.
> If I specify "-c isolinux/boot.cat" too, that fixes it.

Is there any new insight in this mystery ?

If it is reproducible, then my understanding of partitions
is in deep trouble. I'd need to investigate and compare an
ISO with usable partition against one with unusable partition.

Only remotely related:

I found a new compliant partiton layout in the web.
It could avoid the duplication of the EFI partition at the
cost of a second ISO superblock and directory tree, if one
would develop it further.

openSUSE-13.1-NET-x86_64.iso has a mountable ISO filesystem
in MBR partiton 2 and on the base device:

  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x00  0xef          280         8192
  MBR partition      :   2   0x80  0x17         8472       573160
  MBR partition path :   1  /boot/x86_64/efi

Both ISO directory trees share most data files in the ISO.
Only their files /boot/x86_64/efi are located in different
content blocks.

If i get it right, then
lets mkisofs produce a first ISO with EFI FAT as first data
file. The head of this ISO is cut off after the content of
the EFI FAT. The rest (rump) of the first ISO is thrown away. 

The harvested ISO head is then brought as data file into the
second, final ISO. There it is stored as second file after
the EFI FAT, where partition 1 ends and partition 2 begins.
(It gets hidden from the directory tree in the second ISO,
but that's not really needed for the trick.)

Because both mkisofs runs sort the other data file blocks
to the same sequence, the ISO head gets retransplanted to
an identical copy of its old rump.
So partiton 2 becomes mountable as ISO 9660.

This layout is still as wasteful as xorriso appended partition
plus partition offset 16.
But it should be possible to substitute the duplicate FAT
image file in the second ISO by a missing FAT image file
in the first ISO. The first ISO is only for mounting as
partition 2. The El Torito boot image and FAT partition 1
are needed in the second, outer ISO.


Have a nice day :)


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