tracing: Use str_has_prefix() instead of using fixed sizes

There are several instances of strncmp(str, "const", 123), where 123 is the
strlen of the const string to check if "const" is the prefix of str. But
this can be error prone. Use str_has_prefix() instead.
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -4411,7 +4411,7 @@ static int trace_set_options(struct trace_array *tr, char *option)
 
 	cmp = strstrip(option);
 
-	if (strncmp(cmp, "no", 2) == 0) {
+	if (str_has_prefix(cmp, "no")) {
 		neg = 1;
 		cmp += 2;
 	}

kernel/trace/trace_events.c

@@ -1251,7 +1251,7 @@ static int f_show(struct seq_file *m, void *v)
 	 */
 	array_descriptor = strchr(field->type, '[');
 
-	if (!strncmp(field->type, "__data_loc", 10))
+	if (str_has_prefix(field->type, "__data_loc"))
 		array_descriptor = NULL;
 
 	if (!array_descriptor)

kernel/trace/trace_events_hist.c

@@ -518,7 +518,7 @@ static int synth_event_define_fields(struct trace_event_call *call)
 
 static bool synth_field_signed(char *type)
 {
-	if (strncmp(type, "u", 1) == 0)
+	if (str_has_prefix(type, "u"))
 		return false;
 
 	return true;

kernel/trace/trace_probe.c

@@ -194,7 +194,7 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
 			code->op = FETCH_OP_RETVAL;
 		else
 			ret = -EINVAL;
-	} else if (strncmp(arg, "stack", 5) == 0) {
+	} else if (str_has_prefix(arg, "stack")) {
 		if (arg[5] == '\0') {
 			code->op = FETCH_OP_STACKP;
 		} else if (isdigit(arg[5])) {
@@ -213,7 +213,7 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
 #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
 	} else if (((flags & TPARG_FL_MASK) ==
 		    (TPARG_FL_KERNEL | TPARG_FL_FENTRY)) &&
-		   strncmp(arg, "arg", 3) == 0) {
+		   str_has_prefix(arg, "arg")) {
 		if (!isdigit(arg[3]))
 			return -EINVAL;
 		ret = kstrtoul(arg + 3, 10, &param);

kernel/trace/trace_stack.c

@@ -448,7 +448,7 @@ static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;
 
 static __init int enable_stacktrace(char *str)
 {
-	if (strncmp(str, "_filter=", 8) == 0)
+	if (str_has_prefix(str, "_filter="))
 		strncpy(stack_trace_filter_buf, str+8, COMMAND_LINE_SIZE);
 
 	stack_tracer_enabled = 1;