Re: [PATCH v2] tracing: Use seq_buf for string concatenation

On 30/6/2569 BE 01:39, Steven Rostedt wrote:

On Mon, 22 Jun 2026 16:46:23 +0700
Woradorn Laodhanadhaworn [off-list ref] wrote:

quoted

 
 #include <trace/events/sched.h>
 #include <trace/syscall.h>

@@ -4500,14 +4501,20 @@ static void __add_event_to_tracers(struct trace_event_call *call)
 extern struct trace_event_call *__start_ftrace_events[];
 extern struct trace_event_call *__stop_ftrace_events[];
 
-static char bootup_event_buf[COMMAND_LINE_SIZE] __initdata;

Keep the above string and just assign it.

quoted

+static struct seq_buf bootup_event_buf __initdata = {
+	.buffer = (char[COMMAND_LINE_SIZE]) {},
+	.size = COMMAND_LINE_SIZE,
+};

static struct seq_buf bootup_event_seq __initdata = {
	.buffer = bootup_event_buf;
	.size = sizeof(bootup_event_buf);
};

quoted

 
 static __init int setup_trace_event(char *str)
 {
-	if (bootup_event_buf[0] != '\0')
-		strlcat(bootup_event_buf, ",", COMMAND_LINE_SIZE);
+	if (seq_buf_used(&bootup_event_buf) > 0)
+		seq_buf_puts(&bootup_event_buf, ",");
+
+	seq_buf_puts(&bootup_event_buf, str);
 
-	strlcat(bootup_event_buf, str, COMMAND_LINE_SIZE);
+	if (seq_buf_has_overflowed(&bootup_event_buf))
+		return -ENOMEM;
 
 	trace_set_ring_buffer_expanded(NULL);
 	disable_tracing_selftest("running event tracing");

@@ -4766,7 +4773,7 @@ static __init int event_trace_enable(void)
 	 */
 	__trace_early_add_events(tr);
 
-	early_enable_events(tr, bootup_event_buf, false);
+	early_enable_events(tr, (char *)seq_buf_str(&bootup_event_buf), false);

The above then would be:

	seq_buf_str(&bootup_event_seq);
	early_enable_events(tr, bootup_event_buf, false);

Don't typecast a const char* to non const.

quoted

 
 	trace_printk_start_comm();
 

@@ -4794,7 +4801,7 @@ static __init int event_trace_enable_again(void)
 	if (!tr)
 		return -ENODEV;
 
-	early_enable_events(tr, bootup_event_buf, true);
+	early_enable_events(tr, (char *)seq_buf_str(&bootup_event_buf), true);

Same here.

-- Steve

quoted

 
 	return 0;
 }

Thank you, Steven, for your review. I've sent v4:
https://lore.kernel.org/all/20260713045249.69942-1-woradorn.laon@gmail.com (local)

Thanks,
Woradorn