Add basic readlink command

Change-Id: I693c1098e6c6d107a9e97285bf826ab153a1c8f0

toolbox/Android.mk

@@ -68,7 +68,8 @@ TOOLS := \
 	load_policy \
 	swapon \
 	swapoff \
-	mkswap
+	mkswap \
+	readlink
 
 ifneq (,$(filter userdebug eng,$(TARGET_BUILD_VARIANT)))
 TOOLS += r

toolbox/readlink.c

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2013, The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *  * Neither the name of Google, Inc. nor the names of its contributors
+ *    may be used to endorse or promote products derived from this
+ *    software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+static void usage(char* name) {
+    fprintf(stderr, "Usage: %s FILE\n", name);
+}
+
+int readlink_main(int argc, char* argv[]) {
+    if (argc != 2) {
+        usage(argv[0]);
+        return EXIT_FAILURE;
+    }
+
+    char name[PATH_MAX+1];
+    ssize_t len = readlink(argv[1], name, PATH_MAX);
+
+    if (len < 0) {
+        perror("readlink");
+        return EXIT_FAILURE;
+    }
+
+    name[len] = '\0';
+    printf("%s\n", name);
+
+    return EXIT_SUCCESS;
+}