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

[Vladimir 'φ-coder/phcoder' Serbinenko]

Thomas Schmitt wrote:
> 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 ?
>
>   
Floppy. (supported for image sizes smaller than 1.44 MiB)
> 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.
>
>   
Yes, grub-mkisofs code is a stub. What I described is a correct table
> 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 ?
>   
Yes
> Is my C/H/S computation ok ?
>   
It looks fine
> -------------------------------------------------
>
> 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.
>   
We probably need a way to choose a subset of modules for floppies
>  
> 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.)
>
>   
Perhaps as an option, not as default.
> ------------------------------------------------
>
> 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.
>
>   
msdos is the name of this partition label
> -------------------------------------------------
>
>
> Have a nice day :)
>
> Thomas
>
>
>
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>
>   


-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko

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