df does not show btrfs filesystem

[Ulli Horlacher]

"df -T ." (from Ubuntu 16.04 coreutils 8.25-2ubuntu2) does not show btrfs
filesystem (subvolume):

root@diaspora:/local/home# df -T .
Filesystem Type 1K-blocks Used Available Use% Mounted on
- - 926429912 398092364 527962324 43% /local/home

root@diaspora:/local# df -T .
Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/sda4 btrfs 926429912 398092540 527962164 43% /local

root@diaspora:/local# df -T | grep ^/dev
/dev/sda2 ext4 16382888 8614260 6913384 56% /
/dev/sda3 ext4 16382888 185016 15342628 2% /tmp
/dev/sda4 btrfs 926429912 398092360 527962328 43% /local

root@diaspora:/local# mount | grep btrfs
/dev/sda4 on /local type btrfs (rw,relatime,ssd,space_cache,subvolid=5,subvol=/)

root@diaspora:/local# blkid | grep sda4
/dev/sda4: LABEL="local" UUID="11faaa39-5805-4e92-a891-e8ceb4afa9f7" UUID_SUB="787a362f-ba60-44ca-a49f-6ff37eb691d4" TYPE="btrfs" PARTUUID="c93790e9-04"

root@diaspora:/local# btrfs filesystem show /local
Label: 'local' uuid: 11faaa39-5805-4e92-a891-e8ceb4afa9f7
        Total devices 1 FS bytes used 379.48GiB
        devid 1 size 883.51GiB used 414.02GiB path /dev/sda4

root@diaspora:/local# btrfs subvolume list /local
ID 270 gen 42626 top level 5 path data
ID 271 gen 1046 top level 5 path tmp
ID 622 gen 43690 top level 5 path home

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Seb35 (seb35)]

Also affects Ubuntu 20.04 LTS (and other distributions like Debian 10).

Indirectly reported upstream on https://debbugs.gnu.org/cgi/bugreport.cgi?bug=17676 "btrfs subvolumes and bind-mounts make df report incorrect and/or extra results" (the reported bug is a consequence of the issue on btrfs subvolumes).