+
+/*
+ * Older glibc <sys/mount.h> headers did not define all the available
+ * umount2(2) flags. Both MNT_FORCE and MNT_DETACH are supported in the
+ * kernel back to 2.4.11 so we define them correctly if they are missing.
+ */
+#ifdef MNT_FORCE
+# define MS_FORCE MNT_FORCE
+#else
+# define MS_FORCE 0x00000001
+#endif /* MNT_FORCE */
+
+#ifdef MNT_DETACH
+# define MS_DETACH MNT_DETACH
+#else
+# define MS_DETACH 0x00000002
+#endif /* MNT_DETACH */
+
+/*
+ * Overlay mount is default in Linux, but for solaris/zfs
+ * compatibility, MS_OVERLAY is defined to explicitly have the user
+ * provide a flag (-O) to mount over a non empty directory.
+ */
+#define MS_OVERLAY 0x00000004