Merge pull request #42 from OpenCloudOS/dev

some small optimization

Author: menglongdong

src/dropreason.c

@@ -18,7 +18,8 @@ static bool drop_reason_inited = false;
 bool drop_reason_support()
 {
 	return simple_exec("cat /sys/kernel/debug/tracing/events/skb/"
-			   "kfree_skb/format | grep NOT_SPECIFIED") == 0;
+			   "kfree_skb/format 2>/dev/null | "
+			   "grep NOT_SPECIFIED") == 0;
 }
 
 static int parse_reason_enum()

src/trace.c

@@ -375,19 +375,39 @@ static int trace_prepare_traces()
 int trace_prepare()
 {
 	trace_t *trace;
+	int err;
 
-	if (trace_prepare_args())
-		return -1;
+	err = trace_prepare_args();
+	if (err)
+		goto err;
 
-	if (trace_prepare_traces())
-		return -1;
+	err = trace_prepare_traces();
+	if (err)
+		goto err;
 
 	if (trace_ctx.args.show_traces) {
 		trace_show(&root_group);
 		exit(0);
 	}
 
+	if (geteuid() != 0) {
+		pr_err("Please run as root!\n");
+		err = -EPERM;
+		goto err;
+	}
+
+#ifndef COMPAT_MODE
+	if (!file_exist("/sys/kernel/btf/vmlinux")) {
+		pr_err("BTF is not support by your kernel, please compile"
+		       "this tool with \"COMPAT=1\"\n");
+		err = -ENOTSUP;
+		goto err;
+	}
+#endif
+
 	return 0;
+err:
+	return err;
 }
 
 static int trace_bpf_load()