bug#40043: `guix pack --format=squashfs` fails on CentOS7

[Ludovic Courtès]

Hi Josh,

Josh Marshall <address@hidden> skribis:

> `guix pack --format=squashfs bash-minimal ...` fails on CentOS7 with SELinux 
> disabled.
>
> ```
> $ /var/guix/profiles/per-user/marshjo/current-guix/bin/guix describe
> Generation 9  Mar 12 2020 09:28:29    (current)
>   guix a595399
>     repository URL: https://git.savannah.gnu.org/git/guix.git
>     branch: master
>     commit: a595399230a7b1acb0b096b3d5a7474100014299
> ```

The log you posted reads this:

--8<---------------cut here---------------start------------->8---
Creating 4.0 filesystem on 
/gnu/store/mhhlqyazyvwz72y6dwh56fs1zlrvrl0h-squashfs-pack.gz.squashfs, block 
size 131072.

[...]

Number of uids 2
        unknown (0)
        nixbld (987)
Number of gids 2
        unknown (0)
        nixbld (980)
Failed to read existing filesystem - will not overwrite - ABORTING!
--8<---------------cut here---------------end--------------->8---

I was able to reproduce it on a CentOS 7 system and to strace the
‘mksquashfs’ process, and found that this had to do with access to
SELinux extended attributes.

Fixed in commit 53c594cb3f1f783fea18be6da23a863b00c14f5f.

Thanks!

Ludo’.