[syslinux] isohybrid and ISO images whose size is not a multiple of 2048 bytes vs. VirtualBox

[Didier Spaier]

Hi,

On 20/02/2015 11:29, Thomas Schmitt via Syslinux wrote:
> Hi,
>
>> Now, I have a question:  what about the "offset" parameter? How it
>> modifies our assumptions and calculations if the "offset" parameter is
>> not zero?
>
> The offset influences only the start address of the
> partition. The alignment goal is about the end address.
> So these concepts are nearly independent.
>
> Of course, partition start must be smaller than partition
> end. But a mountable ISO cannot be smaller than
> 18 * 2048 bytes = 72 in units of -o. And -o is limited
> to 64. (Not so clear why ...)
>
>
> A non-zero offset makes the MBR ISO partition unmountable
> unless the ISO is specially prepared by a second superblock
> and directory tree.
> So isohybrid option -o is for experts, anyway.
>
> The ISO partition covers the block range at least up to
> the end of the ISO filesystem and includes the padding.
> Even if it is not mountable, it still protects the ISO
> filesystem from being regarded as free space by partition
> editors.
>
>
>> Perhaps the code will
>> be more clear to me when I'll see it included in isohybrid.c
>
> This is a patch against
>    http://git.kernel.org/cgit/boot/syslinux/syslinux.git/plain/utils/isohybrid.c

Once testing will have been performed, could a patch be provided
against the code in release 6.03 (I don't know if it differs
from the one in git), and also against the code in stable releases
4.06 and 4.07?[1]

[1]Unless it be applied in a maintenance release, of course.

Thanks in advance and best regards,

Didier