bug#35283: ISO images are not reproducible

["Ludovic Courtès" <ludo@gnu.org>]

Hi,

"Thomas Schmitt" <scdbackup@gmx.net> skribis:

>>   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 ?

Files in /gnu/store, by convention, all have their mtime set to 1 (one
second after the epoch).

>>  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.)

AFAICS, setting SOURCE_DATE_EPOCH didn’t have a noticeable impact on
Xorriso, or at least it was overridden by the “-volume_date” options
that I pass.

It’s crucial for me to have the mtime set to 1 for all the files on the
ISO; I wanted the 1980 setting to apply only to ‘efi.img’.

>>   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.

I haven’t dig deep enough to provide a satisfactory answer.  :-)

>>   1b0b1651b1 gnu: mtools: 'mformat' initializes boot sector before writing
>
> How good are chances to bring such changes into upstream ?

I’ve emailed them (actually tried to, their mailing list rejected my
message.)  We’ll see!

Ludo’.