Problem: UUIDs not being used everywhere for disks in stretch

[Steve McIntyre <steve@einval.com>]

Hey folks,

Leif (in CC) pointed this out to me after he did a fresh Stretch
installation over the weekend. I've just verified the problem
myself. Our initial thought was that this might be specific to
installations onto NVME, but I've tested and it's not, it's generic.

Right at the end of a simple installation to a single disk device,
when we run grub-installer, the generated grub.cfg is using
root=/dev/XXXX for the kernel command line rather than what it should
be (root=UUID=YYYY). This bug has managed to slip through our
installation testing as the resulting system will still boot fine for
simple single-disk cases...

I've compared this to a jessie installation using the same setup, and
that did the right thing (i.e. the final grub.cfg used
root=UUID=YYYY).  I've spent some time tracking down what's going on,
and I can see the *first* level of problem at least.

In grub-mkconfig, it looks for entries in /dev/disk/by-uuid/ to match
the UUID for /. If it can't find one, it falls back to using the
direct /dev/ disk device for the rootfs. Checking back, I can see:

 * in jessie, the entries in /dev/disk/by-uuid/ are refreshed after
   we're finished in partman

 * in stretch, they are not. You can see this most obviously - start
   with a blank disk and the only entry that will show up in there
   throughout the installation is for the installation medium

Does anybody have any insights as to how this might have
changed/broken? I'm too tired to dig much further tonight, but I'll
carry on looking tomorrow.

*Finally* - this is not a critical problem in the long run AFAICS. As
soon as people update their grub.cfg in their new system (so a new
kernel, or a new grub, or new versions of various other packages),
the installed system should generate a fixed UUID-style grub.cfg.

-- 
Steve McIntyre, Cambridge, UK.                                steve@einval.com
< Aardvark> I dislike C++ to start with. C++11 just seems to be
            handing rope-creating factories for users to hang multiple
            instances of themselves.