commit 108cc873398932af589c295f78c348513b8d70d9 breaks update-grub on btrfs root filesystem

[Alex Romosan]

Please Cc me as I am not subscribed to the list.

Running my own compiled kernel without initramfs on a lenovo thinkpad
x1 carbon gen 7.  The linux disk is the only disk on the system. Since
version 7.3-rc1 i haven't been able to to a grub-update, instead i get
this error:

/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).

7.2 is fine. a git-bisect identified commit
108cc873398932af589c295f78c348513b8d70d9 as being the culprit.
reverting this commit from 7.3-rc2 allowed me to run grub-update
again.

this is not the first time i reported grub-update being broken on
btrfs. i reported exactly the same problem on jan 8, 2024
(https://lkml.iu.edu/hypermail/linux/kernel/2401.1/00596.html). maybe
the discussion that followed would help come up with a fix that will
make everybody happy.

thank you.

--alex--