bug#27212: [PATCH] file-systems: Improve error handling in the iso9660 case - fixes boot problem.

[Danny Milosavljevic]

Hi,

sorry for the slip-up.

The error handling in 203a9455c4695152fc5d0085bffeead9ce3216c2 was improved for 
the case when there's no iso9660 primary volume descriptor anywhere and no 
terminator either.  In that case the CD is broken.

But if there's no iso9660 volume descriptor AT ALL (primary or not) it's not a 
fatal error for guix gnu/build/file-systems.scm - it just means we picked the 
wrong filesystem type and should try the next one.  This case was not handled 
correctly and this patch addresses this.

I'd like help with testing this patch.  If someone with a fast computer could 
apply this patch, then run make check-system, and then, if everything worked, 
run guix system reconfigure /etc/config.scm , that would be great (my computer 
is building guix master for the last 3 days and probably needs 4 more - so no 
idea whether the patch works).

@Marius: I don't understand why reverting 
203a9455c4695152fc5d0085bffeead9ce3216c2 didn't fix it.  It should have.  (I 
can't try it myself because I'm in forced-system-update purgatory - argh).