If any devices are marked with 'SYSTEMD_READY=0' then we shouldn't run any
btrfs check on them.
Indeed there's no point in running "btrfs ready" on devices that already have
SYSTEMD_READY=0 set. Most probably such devices are members of a higher layer
aggregate device such as dm-multipath or software RAID. Doing IO on them wastes
time at best, and may cause delays, timeouts, or even hangs at worst (think
active-passive multipath or degraded RAID, for example).
It was initially reported at:
https://bugzilla.opensuse.org/show_bug.cgi?id=872929
SUBSYSTEM!="block", GOTO="btrfs_end"
ACTION=="remove", GOTO="btrfs_end"
ENV{ID_FS_TYPE}!="btrfs", GOTO="btrfs_end"
+ENV{SYSTEMD_READY}=="0", GOTO="btrfs_end"
# let the kernel know about this btrfs filesystem, and check if it is complete
IMPORT{builtin}="btrfs ready $devnode"