[Toybox] systemd uses umount -c option which the toybox umount implementation does not process

[Eduardas Meile]

Since I use a combination of toybox and systemd, I have noticed that
systemd fails
to unmount partitions during shutdown when toybox umount is in use.
This is because systemd uses umount -c option and focuses on util-linux.
Systemd is apparently not going to change this behaviour for the
foreseeable future.
It seems busybox also had this same problem not so long ago. They
eventually decided to
simply ignore the -c option since busybox does not canonicalize mount
paths in
the first place (same for toybox?). Relevant discussions:

https://github.com/systemd/systemd/issues/7786

http://lists.busybox.net/pipermail/busybox/2018-January/086045.html

https://git.busybox.net/busybox/commit/?id=426134128112738c97a665170b21153ef0764b7d

I am not sure whether you would be willing to do the same thing for
toybox or
whether what busybox did is even the right solution. I just wanted to
bring this to your attention
since no one has discussed this previously on the mailing list as far as
I am aware of.
I feel like some kind of comment on this would be useful.

As at least a temporary solution I am currently using umount from
util-linux instead
of the toybox umount implementation.

[Rob Landley]

Since I use a combination of toybox and systemd, I have noticed that systemd fails

The umount in ubuntu 14.04 doesn't have -c, I googled for a more recent umount
man page and https://linux.die.net/man/8/umount hasn't got it either, but you're
right, busybox started ignoring this.

*shrug* Sure?

Rob