rtla: Use str_has_prefix() for prefix checks

The code currently uses strncmp() combined with strlen() to check if a
string starts with a specific prefix. This pattern is verbose and prone
to errors if the length does not match the prefix string.

Replace this pattern with the str_has_prefix() helper function in both
trace.c and utils.c. This improves code readability and safety by
handling the prefix length calculation automatically.

In addition, remove the unused retval variable from
trace_event_save_hist() in trace.c to clean up the function and
silence potential compiler warnings.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Link: https://lore.kernel.org/r/20260309195040.1019085-12-wander@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>

Author: walac

tools/tracing/rtla/src/trace.c

@@ -342,7 +342,7 @@ static void trace_event_disable_filter(struct trace_instance *instance,
 static void trace_event_save_hist(struct trace_instance *instance,
 				  struct trace_events *tevent)
 {
-	int retval, index, out_fd;
+	int index, out_fd;
 	mode_t mode = 0644;
 	char path[MAX_PATH];
 	char *hist;
@@ -356,8 +356,7 @@ static void trace_event_save_hist(struct trace_instance *instance,
 		return;
 
 	/* is this a hist: trigger? */
-	retval = strncmp(tevent->trigger, "hist:", strlen("hist:"));
-	if (retval)
+	if (!str_has_prefix(tevent->trigger, "hist:"))
 		return;
 
 	snprintf(path, ARRAY_SIZE(path), "%s_%s_hist.txt", tevent->system, tevent->event);

tools/tracing/rtla/src/utils.c

@@ -331,8 +331,7 @@ static int procfs_is_workload_pid(const char *comm_prefix, struct dirent *proc_e
 		return 0;
 
 	buffer[MAX_PATH-1] = '\0';
-	retval = strncmp(comm_prefix, buffer, strlen(comm_prefix));
-	if (retval)
+	if (!str_has_prefix(buffer, comm_prefix))
 		return 0;
 
 	/* comm already have \n */