Add getmntent_r to our collection of <mntent.h> compatibility stubs.

This helps build 'external/flo' out of the box.

Bug: 14841211
Change-Id: I30dde77239cceaf1f5743163744eb3604d27a266

tests/mntent_test.cpp

@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+
+#include <mntent.h>
+
+TEST(mntent, mntent_smoke) {
+  FILE* fp = setmntent("/no/mnt/tab/on/android", "r");
+  ASSERT_TRUE(fp == NULL);
+
+#if __BIONIC__ // glibc doesn't let you call getmntent/getmntent_r with a NULL FILE*.
+  ASSERT_TRUE(getmntent(fp) == NULL);
+
+  struct mntent mbuf;
+  char cbuf[32];
+  ASSERT_TRUE(getmntent_r(fp, &mbuf, cbuf, sizeof(cbuf)) == NULL);
+#endif
+
+  ASSERT_EQ(1, endmntent(fp));
+}