Re: [PATCH v5] tracing: Preserve repeated boot-time tracing parameters

[Steven Rostedt]

On Sat, 28 Mar 2026 14:18:42 -0600
Wesley Atwell <atwellwea@xxxxxxxxx> wrote:

> Some tracing boot parameters already accept delimited value lists, but
> their __setup() handlers keep only the last instance seen at boot.
> Make repeated instances append to the same boot-time buffer in the
> format each parser already consumes.
> 
> Use a shared trace_append_boot_param() helper for the ftrace filters,
> trace_options, and kprobe_event boot parameters. trace_trigger=
> tokenizes its backing storage in place, so keep a running offset and
> only parse the newly appended chunk into bootup_triggers[].
> 
> This also lets Bootconfig array values work naturally when they expand
> to repeated param=value entries.
> 
> Validated by booting with repeated ftrace_filter=, ftrace_notrace=,
> ftrace_graph_filter=, ftrace_graph_notrace=, trace_options=,
> kprobe_event=, and trace_trigger= parameters and confirming that the
> resulting tracefs state preserved every requested entry. Before this
> change, only the last instance from each repeated parameter survived
> boot.
> 
> Signed-off-by: Wesley Atwell <atwellwea@xxxxxxxxx>
> ---
> v5:

FYI, it's nice to have a daisy chain connection of previous versions. I
suggest instead of just saying "v5:" use:

Changes since v4: https://lore.kernel.org/all/20260324221326.1395799-2-atwellwea@xxxxxxxxx/

> - use int sizes in the shared append helper and trace_trigger bookkeeping
> - keep a single bounded append path that only inserts the separator after
>   the first entry
> - only advance the trace_trigger buffer offset after a successful append
> 
>  kernel/trace/ftrace.c       | 12 ++++++++----
>  kernel/trace/trace.c        | 29 ++++++++++++++++++++++++++++-
>  kernel/trace/trace.h        |  2 ++
>  kernel/trace/trace_events.c | 23 ++++++++++++++++++++---
>  kernel/trace/trace_kprobe.c |  3 ++-
>  5 files changed, 60 insertions(+), 9 deletions(-)
> 

> +/*
> + * Repeated boot parameters, including Bootconfig array expansions, need
> + * to stay in the delimiter form that the existing parser consumes.
> + */
> +void __init trace_append_boot_param(char *buf, const char *str, char sep,
> +				    int size)
> +{

This is much better.

> +	int len, needed, str_len;
> +
> +	if (!*str)
> +		return;
> +
> +	len = strlen(buf);
> +	str_len = strlen(str);
> +	needed = len + str_len + 1;

Perhaps add a comment:

	/* For continuation, account for separator */
> +	if (len)
> +		needed++;
> +	if (needed > size)
> +		return;
> +
> +	if (len)
> +		buf[len++] = sep;
> +
> +	strscpy(buf + len, str, size - len);
> +}
> +
>  static int __init set_cmdline_ftrace(char *str)
>  {
>  	strscpy(bootup_tracer_buf, str, MAX_TRACER_SIZE);


> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -3679,20 +3679,37 @@ static struct boot_triggers {
>  } bootup_triggers[MAX_BOOT_TRIGGERS];
>  
>  static char bootup_trigger_buf[COMMAND_LINE_SIZE];
> +static int bootup_trigger_buf_len;
>  static int nr_boot_triggers;
>  
>  static __init int setup_trace_triggers(char *str)
>  {
> +	char *slot;
>  	char *trigger;
>  	char *buf;
>  	int i;
>  
> -	strscpy(bootup_trigger_buf, str, COMMAND_LINE_SIZE);
> +	if (bootup_trigger_buf_len >= COMMAND_LINE_SIZE)
> +		return 1;
> +
> +	slot = bootup_trigger_buf + bootup_trigger_buf_len;

The bootup_trigger_buf is a temporary buffer for this function only. It
works fine as is. There's no reason to modify this function.

-- Steve

> +
> +	/*
> +	 * trace_trigger= parsing tokenizes the backing storage in place.
> +	 * Copy each repeated parameter into fresh space and only parse that
> +	 * newly copied chunk here.
> +	 */
> +	trace_append_boot_param(slot, str, '\0',
> +				COMMAND_LINE_SIZE - bootup_trigger_buf_len);
> +	if (!*slot)
> +		return 1;
> +
> +	bootup_trigger_buf_len += strlen(slot) + 1;
>  	trace_set_ring_buffer_expanded(NULL);
>  	disable_tracing_selftest("running event triggers");
>  
> -	buf = bootup_trigger_buf;
> -	for (i = 0; i < MAX_BOOT_TRIGGERS; i++) {
> +	buf = slot;
> +	for (i = nr_boot_triggers; i < MAX_BOOT_TRIGGERS; i++) {
>  		trigger = strsep(&buf, ",");
>  		if (!trigger)
>  			break;