umount --all-targets only unmounts partitions not all partitions on a device

[ProBackup-nl]

Having /dev/sdb2 mounted in /mnt/sdb2,
and having read comment 1 from the year 2013 for bug 916216, especially the code sample:

for pid in $(ps --no-headers -xao pid); do 
   nsenter -t $pid umount --recursive --all-targets /dev/sdb
done

I would have expected "umount from util-linux 2.32.1 (libmount 2.32.1: btrfs, assert, debug)" option --all-targets to function when a device without partition number is specified.

Actual result:

# mount /dev/sdb2 /mnt/sdb2
# umount --recursive --all-targets /dev/sdb
umount: /dev/sdb: not mounted

Expected result:

# umount --recursive --all-targets /dev/sdb
[root@d2 ~]# lsblk /dev/sdb2
NAME MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sdb2   8:18   1 28.7G  0 part

Note: even the code sample above doesn't result in all partitions on /dev/sdb to get unmounted.

Is my expectation wrong?

PS Otherwise it would be nice to have a -quiet or -noerror flag, so one can execute
# umount --recursive --all-targets /dev/sdb*
without the "not mounted" output:

umount: /dev/sdb: not mounted
umount: /dev/sdb1: not mounted

[karelzak]

Unfortunately your expectation is wrong. The command umount has no clue about whole-disk and partitions concept. It works with individual block devices only. The solution is to use sdb*.

The options -quiet seems like good idea -- I'll implement it.