When systemd-loop@.service is instantiated for a block device (e.g. a
CD-ROM drive, which is the primary usecase now that --relax is used),
%f resolves to the backing block device rather than to the loopback
block device that was attached on top of it. In that case ExecStop=
hence invoked --detach on a block device that is not a loopback device
at all, which made loop_device_set_autoclear() a silent no-op, leaking
the attachment.
Hence, if --detach is passed a block device that is not a loopback
block device itself, search for the loopback block device backed by it,
the same way we already do for regular files. The kernel reports the
backing inode for block device nodes too, so the same inode matching
logic applies.
Lennart Poettering
b8ee13613c