Add utility for cc tests to read command outputs

This introduces a separate source file for adding common
utilities which can be used by any of the cc tests. For
now, we add a function to read values from the output of
a command with a format string like scanf().
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>

tests/cc/CMakeLists.txt

@@ -17,7 +17,8 @@ add_executable(test_libbcc
 	test_bpf_table.cc
 	test_hash_table.cc
 	test_usdt_args.cc
-	test_usdt_probes.cc)
+	test_usdt_probes.cc
+	utils.cc)
 
 target_link_libraries(test_libbcc bcc-shared dl)
 add_test(NAME test_libbcc COMMAND ${TEST_WRAPPER} c_test_all sudo ${CMAKE_CURRENT_BINARY_DIR}/test_libbcc)

tests/cc/utils.cc

+/*
+ * Copyright (c) 2017 IBM Corporation
+ *
+ * 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 <stdarg.h>
+#include <stdio.h>
+
+int cmd_scanf(const char *cmd, const char *fmt, ...) {
+  va_list args;
+  FILE *pipe;
+
+  va_start(args, fmt);
+  pipe = popen(cmd, "r");
+  if (pipe == NULL) {
+    va_end(args);
+    return -1;
+  }
+
+  vfscanf(pipe, fmt, args);
+  va_end(args);
+  pclose(pipe);
+  return 0;
+}