[systemd-devel] unit A is WantedBy unit B but unit B does not Want unit A?

[Andrei Borzenkov]

Sometimes device gets Wants on mount point; sometimes not. I do not
really understand why. Also different mount units apparently behave
differently - e.g. mnt.mount "forgets" its history. It almost looks like
mnt.mount is destroyed after it is unmounted and t.mount not ...

cat /etc/fstab
UUID=ec5c431d-52a3-4e50-b7d0-2086c82d6f4b swap                 swap       defaults              0 0
UUID=8b291227-1d97-4dcf-b7a7-35be000a3643 /                    ext4       acl,user_xattr        1 1
UUID=cdae3bb7-7462-4b86-bc30-ff7e48f815d0 /boot                ext2       acl,user_xattr        1 2
UUID="ee092e94-48c8-464a-958d-967810227fff" /t			btrfs	nofail	1 2
cat /etc/systemd/system/mnt.mount
[Unit]
Description=/mnt

[Mount]
What=/dev/disk/by-uuid/ee092e94-48c8-464a-958d-967810227fff
Where=/mnt
Type=btrfs
Options=rw
systemctl status t.mount mnt.mount
t.mount - /t
   Loaded: loaded (/etc/fstab)
   Active: inactive (dead) since Sat 2014-11-01 19:38:01 MSK; 2min 53s ago
    Where: /t
     What: /dev/disk/by-uuid/ee092e94-48c8-464a-958d-967810227fff
  Process: 1293 ExecMount=/bin/mount -n -t btrfs -o nofail /dev/disk/by-uuid/ee092e94-48c8-464a-958d-967810227fff /t (code=exited, status=0/SUCCESS)


mnt.mount - /mnt
   Loaded: loaded (/etc/systemd/system/mnt.mount; static)
   Active: inactive (dead)
    Where: /mnt
     What: /dev/disk/by-uuid/ee092e94-48c8-464a-958d-967810227fff

systemctl show -p WantedBy t.mount mnt.mount
WantedBy=local-fs.target dev-disk-by\x2duuid-ee092e94\x2d48c8\x2d464a\x2d958d\x2d967810227fff.device

WantedBy=dev-disk-by\x2duuid-ee092e94\x2d48c8\x2d464a\x2d958d\x2d967810227fff.device
systemctl show -p Wants dev-disk-by\x2duuid-ee092e94\x2d48c8\x2d464a\x2d958d\x2d967810227fff.device
Wants=t.mount