+static int dir_is_mount_point(DIR *d, const char *subdir) {
+ struct file_handle *h;
+ int mount_id_parent, mount_id;
+ int r_p, r;
+
+ h = alloca(MAX_HANDLE_SZ);
+
+ h->handle_bytes = MAX_HANDLE_SZ;
+ r_p = name_to_handle_at(dirfd(d), ".", h, &mount_id_parent, 0);
+ if (r_p < 0)
+ r_p = -errno;
+
+ h->handle_bytes = MAX_HANDLE_SZ;
+ r = name_to_handle_at(dirfd(d), subdir, h, &mount_id, 0);
+ if (r < 0)
+ r = -errno;
+
+ /* got no handle; make no assumptions, return error */
+ if (r_p < 0 && r < 0)
+ return r_p;
+
+ /* got both handles; if they differ, it is a mount point */
+ if (r_p >= 0 && r >= 0)
+ return mount_id_parent != mount_id;
+
+ /* got only one handle; assume different mount points if one
+ * of both queries was not supported by the filesystem */
+ if (r_p == -ENOSYS || r_p == -ENOTSUP || r == -ENOSYS || r == -ENOTSUP)
+ return true;
+
+ /* return error */
+ if (r_p < 0)
+ return r_p;
+ return r;
+}
+