bug#35283: ISO images are not reproducible

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

Hi,

>   833480cc1f vm: Reset file timestamps in ISO images.

That's also a big solution for the problem of timestamps of synthetic files.

I understand that your plan for reproducibility is to make timestamps
completely insignificant. Radical but effective.

But since you set in commit 6901b9248e SOURCE_DATE_EPOCH to 1980, why not
use the same seconds value for the ISO file objects ?


>  6901b9248e vm: Reset file timestamps of the EFI image in ISO images.

Maybe the commit message should have mentioned that setting SOURCE_DATE_EPOCH
not only influences mformat underneath grub-mkrescue, but also the run
of xorriso, where it determines volume date timestamps and GPT individual
UUIDs.
(Other impacts of the variable get overridden by the
   -volume_date "all_file_dates"
 command in commit 833480cc1f.)


>   52b5fe5bcf gnu: grub: 'grub-mkrescue' honors 'GRUB_FAT_SERIAL_NUMBER'.

I still riddle why /efi.img in the 0.16.0 ISO has 1.4 MB of size
but grub-mkrescue.c uses mformat -f 2880, which is supposed to produce
a 2.8 MB FAT image.


>   1b0b1651b1 gnu: mtools: 'mformat' initializes boot sector before writing

How good are chances to bring such changes into upstream ?

I ask in the advance assumption that we find a way to make the mformat
image digestible for Florian's Macbook.
(It is clear now that the difference between failure and success is in
 mformat versus mkfs.fat. But the exact point of failure is not found yet.
 I place my bet on the partition entry with start LBA 0.)


Have a nice day :)

Thomas