Bug#1031696: Use of symbolic links in non-free ISO images breaks file system transposition support

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

Hi,

James Addison wrote:
> Something that symlinks can do is to allow image creators to save space by
> by de-duplicating files. [...]

This could be achieved by a bunch of hard links instead of the symbolic
links. In /firmware of firmware-bookworm-DI-alpha1-amd64-netinst.iso
i see only symbolic links to data files. So replacing symlinks by
hardlinks should be technically possible.

xorriso represents hard link siblings in ISO 9660 and Joliet as data files
which use the same data content blocks. So these views of the Debian ISO
would produce separate copies of target and link when both get extracted
to disk.

A Rock Ridge reader could do better by help of the PN entry. But Linux
computes own inode numbers from the byte addresses of the ISO 9660
directory records. So hardlinks do not get represented as such when Linux
mounts an ISO. Thus copying them out of the ISO causes duplication.

This would be a disadvantage of hard links for those people who unpack
Debian ISOs on Linux.


Have a nice day :)

Thomas