This is unnecessary for classic mount-like tasks, but application
may use libmount in situation when the default for probing is not
optimal.

Addresses: https://github.com/util-linux/util-linux/issues/2214
Signed-off-by: Karel Zak <kzak@redhat.com>

* enter original namespace for the final move_mount(), it means that
  the original unshare() (to create the temporary mount) will be
  ineffective for this final step. God bless FD based APIs (setns()
  and open_tree())! ;-)

* improve cleanup code (call umount only once)

* remember private namespace

* update note in man page

Addresses: https://github.com/util-linux/util-linux/pull/2198
Signed-off-by: Karel Zak <kzak@redhat.com>

Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>

Addresses: https://github.com/util-linux/util-linux/pull/2197
Signed-off-by: Karel Zak <kzak@redhat.com>

Signed-off-by: Karel Zak <kzak@redhat.com>

In some cases, for example:

 # mount -t foo,bar,ext4 /dev/sdc /mnt/test

libmount calls fsopen() later (after mount preparation stage), but we
need during preparation check if hook_mount.c stuff (new API) is usable.

Let's do it by dummy fsopen() call.

Signed-off-by: Karel Zak <kzak@redhat.com>

Signed-off-by: Karel Zak <kzak@redhat.com>

Signed-off-by: Karel Zak <kzak@redhat.com>

X-mount.idmap accepts a series of whitespace-separated tokens. We reject
an empty argument but silently accept an argument consisting of whitespace
with no tokens. Test for the empty case more thoroughly.

[kzak@redhat.com: - use skip_blank()]

Signed-off-by: Chris Webb <chris@arachsys.com>
Signed-off-by: Karel Zak <kzak@redhat.com>