Re: How to prepare an ISO 9660 CD for booting via GRUB ?

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i have roughly implemented the missing options
of grub-mkisofs in xorriso and am now comparing
the results.

The ISO image by xorriso boots from CD and from
USB stick. Are there other media types which
would impose a further challenge ?

If so: are there testers who would be willing
to try my ISO image (1.9 MB) on such media ?


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

It seems that grub-mkisofs does not comply much
to the partition table prescription given by
Vladimir.

The image made by grub-mkisofs has 1550336 bytes
= 757 * 2048 , 3028 * 512.
It bears as partition table:

0000660                                    0080
0000700 0000 00cd 0000 0001 0000 ffff ffff 0000
0000720 0000 0000 0000 0000 0000 0000 0000 0000
*
0000760 0000 0000 0000 0000 0000 0000 0000 aa55

(od -x regrettably produces big-endian 16 bit.
 One has to swap:  00cd  is actually  cd 00 .)


The xorriso image is currently a bit larger
(see below).

1966080 bytes
= 960 * 2048 , 3840 * 2048
xorriso -toc reports:
ISO session  :   1 ,        32 ,       754s , ISOIMAGE

Partition table:

Image size is 32 + 754 = 786 * 2048 = 3144 * 512
= 0x0C48
I insert 0x00000C47 as end LBA (= 0c47 0000).
End C/H/S is c0,h49,s57 (= 31xx 0039).

0000660                                    0080
0000700 0002 31cd 0039 0001 0000 0c47 0000 0000
0000720 0000 0000 0000 0000 0000 0000 0000 0000
*
0000760 0000 0000 0000 0000 0000 0000 0000 aa55

Vladimir: does that look ok for you ?
Is 0x0C47 correct to depict image size 0x0C48 ?
Is my C/H/S computation ok ?
(I understand Wikipedia that way, but am not
sure.)

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

xorriso produces a larger image because of 64 kB
multi-session preparations, of 300 kB end padding
and of padding to full 32 kB blocks.
Most of this overhead can already be prevented.
I will see whether i can strip the output to
its net size of 754 sectors.

Nevertheless, neither the image of grub-mkisofs
nor of xorriso fit on a vanilla floppy disk.
 
Is it worth to sacrifice multi-session history
capabilities in order to save 64 kB ?
(If i do not duplicate the ISO superblock then
 i cannot mount older sessions of a multi-session
 ISO image.)


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

Compatibility question:

Is the help text of grub-mkisofs
  --protective-msdos-label    Patch a protective DOS-style label in the image
essential to any frontend of grub-mkisofs ?

I would prefer to print something more neutral.
Like:
  --protective-msdos-label    Patch System Area by partition table
Any DOS connotation should be obvious by the
option name already.

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


Have a nice day :)

Thomas