Bug#841741: grub-probe fails to find GRUB drive

[Heinz Repp]

Package: grub-common
Version: 2.02~beta3-1

distro: stretch, 64bit

After update to 2.02~beta3-1 my system failed to boot with repeated 
blkid usage screens (blkid -t needs NAME=value pair) with any kernel. 
Turns out in initramfs-tools a function calls blkid -t $(DEV) to get the 
details of the root partition, but this throws an error, and finally 
gives up and falls back to a restricted initramfs-shell. Turns out, in 
environment I had: ROOT='UUID=' - feeding this to blkid provokes the 
error. But why was this so?

Turns out, in /boot/grub/grub.cfg all linux command lines had a 
"root=UUID=" - manally inserting the blkid of the root partition enabled 
a successful boot again.

Running update-grub, the blkids where missing again from grub.cfg. In 
grub-mkconfig I saw the UUID is provided by grub-probe, and entering all 
grub-probe calls by hand I found out it throws an error (on all 
partitions tested):

> grub-probe --device /dev/sdb4 --target=fs_uuid 2
> grub-probe: error: cannot find a GRUB drive for /dev/sdb4.  Check your device.map.

and this produces the empty UUID for the root partition. My device.map 
didn't change, and every other partition (instead of /dev/sdb4) gives 
exactly the same error.

As grub-probe from 2.02 beta 2 did work, the recent update has 
introduced a severe bug.

Please fix! As a workaround I have a sed script that enters the UUID 
manually in case of kernel updates.

Heinz Repp