> Op 20-06-2026 19:54 CEST schreef Woradorn Laodhanadhaworn
> <[email protected]>:
>
>
> In preparation for removing the strlcat API[1],
> replace the string concatenation logic with a struct seq_buf,
> which tracks the current position and the remaining space internally.
>
> The backing buffer bootup_event_buf allocation is unchanged.
> Use seq_buf_str() to NUL-terminate before passing to early_enable_events().
>
> Link: https://github.com/KSPP/linux/issues/370 [1]
>
> Signed-off-by: Woradorn Laodhanadhaworn <[email protected]>
> ---
> kernel/trace/trace_events.c | 21 ++++++++++++++++-----
> 1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index c46e623e7e0d..15164723e028 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -22,6 +22,7 @@
> #include <linux/sort.h>
> #include <linux/slab.h>
> #include <linux/delay.h>
> +#include <linux/seq_buf.h>
>
> #include <trace/events/sched.h>
> #include <trace/syscall.h>
> @@ -4501,13 +4502,23 @@ 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;
Isn't this now unused?
> +static struct seq_buf bootup_event_seq;
> +static bool bootup_event_seq_initialized;
>
I think this can be refactored to avoid the bool. And should bootup_event_seq
not be
__initdata?
> static __init int setup_trace_event(char *str)
> {
> - if (bootup_event_buf[0] != '\0')
> - strlcat(bootup_event_buf, ",", COMMAND_LINE_SIZE);
> + if (!bootup_event_seq_initialized) {
> + seq_buf_init(&bootup_event_seq, bootup_event_buf,
> COMMAND_LINE_SIZE);
> + bootup_event_seq_initialized = true;
> + }
> +
> + if (seq_buf_used(&bootup_event_seq) > 0)
> + seq_buf_puts(&bootup_event_seq, ",");
>
> - strlcat(bootup_event_buf, str, COMMAND_LINE_SIZE);
> + seq_buf_puts(&bootup_event_seq, str);
> +
> + if (seq_buf_has_overflowed(&bootup_event_seq))
> + return -ENOMEM;
>
> trace_set_ring_buffer_expanded(NULL);
> disable_tracing_selftest("running event tracing");
> @@ -4766,7 +4777,7 @@ 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_seq), false);
What if trace_event is empty? Then setup_trace_event does not run AFAIK. See the
WARN_ON in seq_buf_str too. Have you tested this?
>
> trace_printk_start_comm();
>
> @@ -4794,7 +4805,7 @@ 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_seq), true);
>
> return 0;
> }
> --
> 2.43.0
Thanks,
Jori.
