+/* Unmount everything mounted under /sysroot.
+ *
+ * We have to unmount in the correct order, so we sort the paths by
+ * longest first to ensure that child paths are unmounted by parent
+ * paths.
+ *
+ * This call is more important than it appears at first, because it
+ * is widely used by both test and production code in order to
+ * get back to a known state (nothing mounted, everything synchronized).
+ */
+static int
+compare_longest_first (const void *vp1, const void *vp2)
+{
+ char * const *p1 = (char * const *) vp1;
+ char * const *p2 = (char * const *) vp2;
+ int n1 = strlen (*p1);
+ int n2 = strlen (*p2);
+ return n2 - n1;
+}
+