libmount: use x-systemd options as X-*

The previous patch introduces X-* options namespace for options
that have to be maintained in user space.

Unfortunately, systemd users already use mount options that are
necessary by umount or another operations. The conclusion from
discussion with systemd guys is to store all the systemd options
in userspace.

It seems better to add one line exception to libmount than force all
fstab users to rename x-systemd to X-systemd.

Addresses: https://github.com/systemd/systemd/pull/3904
Signed-off-by: Karel Zak <kzak@redhat.com>

configure.ac

@@ -1971,6 +1971,7 @@ AS_IF([test "x$with_systemd" != xno], [
       [AC_MSG_ERROR([systemd expected but libsystemd not found])],
     [*:yes],
        AC_DEFINE([HAVE_LIBSYSTEMD], [1], [Define if libsystemd is available])
+       AC_DEFINE([HAVE_SYSTEMD], [1], [Define if systemd should be supported])
   )
 ])
 AM_CONDITIONAL([HAVE_SYSTEMD], [test "x$have_systemd" = xyes])

libmount/src/optmap.c

@@ -160,6 +160,13 @@ static const struct libmnt_optmap userspace_opts_map[] =
 
    { "comment=", MNT_MS_COMMENT, MNT_NOHLPS | MNT_NOMTAB },/* fstab comment only */
 
+   /*
+    * systemd assumes that x-systemd options namespace is available for umount,
+    * let's use the options as X-*
+    */
+#ifdef HAVE_SYSTEMD
+   { "x-systemd", MNT_MS_XPERSIST, MNT_NOHLPS | MNT_PREFIX },		 /* like X-* */
+#endif
    { "X-",      MNT_MS_XPERSIST, MNT_NOHLPS | MNT_PREFIX },              /* X- persistent comments (utab) */
    { "x-",      MNT_MS_XCOMMENT, MNT_NOHLPS | MNT_NOMTAB | MNT_PREFIX }, /* x- fstab only comments */
 

sys-utils/mount.8

@@ -1154,6 +1154,10 @@ that maintain mount options in user space is a bad idea, because it's necessary
 to link all tools that use the options with libmount and there is no guarantee that the
 options will be always available (for example after a move mount operation or in
 unshared namespace).
+
+Note that x-systemd mount options are maintained as X-* options, the rename is
+unnecessary to keep existing fstab settings backwardly compatible.
+
 .TP
 .BR x-mount.mkdir [ = \fImode\fR ]
 Allow to make a target directory (mountpoint).  The optional argument