Re: [PATCH v6] tracing: Preserve repeated boot-time tracing parameters

[Steven Rostedt]

On Sun, 29 Mar 2026 12:42:54 -0600
Wesley Atwell <atwellwea@xxxxxxxxx> wrote:

BTW, please do not reply to old versions of a patch with new versions. It
makes it much more difficult for maintainers to find what is the last patch.

New versions of a patch should *always* be a start of a new thread!

> 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=
> still tokenizes a temporary parse buffer in place, but now copies each
> parsed event/trigger pair into boot-time storage so repeated instances
> do not overwrite earlier ones.
> 
> This also lets Bootconfig array values work naturally when they expand
> to repeated param=value entries.
> 
> Before this change, only the last instance from each repeated
> parameter survived boot.
> 
> Signed-off-by: Wesley Atwell <atwellwea@xxxxxxxxx>
> ---
> Changes since v5: https://lore.kernel.org/all/20260328201842.1782806-1-atwellwea@xxxxxxxxx/

This is also why I suggested using the above link. The link shows how to
find the old version of the patch, without relying on "In-Reply-To" header.

> - add the separator accounting comment in trace_append_boot_param()
> - keep the existing trace_trigger= temporary buffer and copy each
>   parsed event/trigger pair into boot-time storage instead of tracking
>   a running offset inside that buffer
> 
>  kernel/trace/ftrace.c       | 12 ++++++++----
>  kernel/trace/trace.c        | 30 +++++++++++++++++++++++++++++-
>  kernel/trace/trace.h        |  2 ++
>  kernel/trace/trace_events.c | 24 +++++++++++++++++++++---
>  kernel/trace/trace_kprobe.c |  3 ++-
>  5 files changed, 62 insertions(+), 9 deletions(-)
> 

> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -228,6 +228,33 @@ static int boot_instance_index;
>  static char boot_snapshot_info[COMMAND_LINE_SIZE] __initdata;
>  static int boot_snapshot_index;
>  
> +/*
> + * 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)
> +{
> +	int len, needed, str_len;
> +
> +	if (!*str)
> +		return;
> +
> +	len = strlen(buf);
> +	str_len = strlen(str);
> +	needed = len + str_len + 1;

Nit, but it would be nice to have a blank line here.

> +	/* For continuation, account for the 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);
> @@ -329,7 +356,8 @@ static char trace_boot_options_buf[MAX_TRACER_SIZE] __initdata;
>  
>  static int __init set_trace_boot_options(char *str)
>  {
> -	strscpy(trace_boot_options_buf, str, MAX_TRACER_SIZE);
> +	trace_append_boot_param(trace_boot_options_buf, str, ',',
> +				MAX_TRACER_SIZE);
>  	return 1;
>  }
>  __setup("trace_options=", set_trace_boot_options);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index b8f3804586a0..237a0417de1c 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -863,6 +863,8 @@ extern int DYN_FTRACE_TEST_NAME(void);
>  extern int DYN_FTRACE_TEST_NAME2(void);
>  
>  extern void trace_set_ring_buffer_expanded(struct trace_array *tr);
> +void __init trace_append_boot_param(char *buf, const char *str,
> +				    char sep, int size);
>  extern bool tracing_selftest_disabled;
>  
>  #ifdef CONFIG_FTRACE_STARTUP_TEST
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 249d1cba72c0..1c4a4a46169e 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -17,6 +17,7 @@
>  #include <linux/kthread.h>
>  #include <linux/tracefs.h>
>  #include <linux/uaccess.h>
> +#include <linux/memblock.h>
>  #include <linux/module.h>
>  #include <linux/ctype.h>
>  #include <linux/sort.h>
> @@ -3674,7 +3675,7 @@ trace_create_new_event(struct trace_event_call *call,
>  #define MAX_BOOT_TRIGGERS 32
>  
>  static struct boot_triggers {
> -	const char		*event;
> +	char			*event;
>  	char			*trigger;
>  } bootup_triggers[MAX_BOOT_TRIGGERS];
>  
> @@ -3683,6 +3684,7 @@ static int nr_boot_triggers;
>  
>  static __init int setup_trace_triggers(char *str)
>  {
> +	char *event;
>  	char *trigger;
>  	char *buf;
>  	int i;
> @@ -3692,14 +3694,30 @@ static __init int setup_trace_triggers(char *str)
>  	disable_tracing_selftest("running event triggers");
>  
>  	buf = bootup_trigger_buf;
> -	for (i = 0; i < MAX_BOOT_TRIGGERS; i++) {
> +	for (i = nr_boot_triggers; i < MAX_BOOT_TRIGGERS; i++) {

Let's not make this so complex.

This function isn't the same as the other functions. It doesn't need to add
separators to the temp buffer. It only needs to append it.


>  		trigger = strsep(&buf, ",");
>  		if (!trigger)
>  			break;
> -		bootup_triggers[i].event = strsep(&trigger, ".");
> +		event = strsep(&trigger, ".");
>  		bootup_triggers[i].trigger = trigger;
>  		if (!bootup_triggers[i].trigger)
>  			break;
> +
> +		/*
> +		 * Keep each parsed trigger outside the temporary setup
> +		 * buffer so repeated trace_trigger= entries do not
> +		 * overwrite earlier ones.
> +		 */
> +		bootup_triggers[i].event =
> +			memblock_alloc_or_panic(strlen(event) + 1,
> +						SMP_CACHE_BYTES);
> +		strscpy(bootup_triggers[i].event, event,
> +			strlen(event) + 1);
> +		bootup_triggers[i].trigger =
> +			memblock_alloc_or_panic(strlen(trigger) + 1,
> +						SMP_CACHE_BYTES);
> +		strscpy(bootup_triggers[i].trigger, trigger,
> +			strlen(trigger) + 1);
>  	}

I believe all you need for the boot triggers is this:

  (Not even compiled tested)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 9928da636c9d..7754a8adb58a 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -3677,20 +3677,24 @@ static struct boot_triggers {
 } bootup_triggers[MAX_BOOT_TRIGGERS];
 
 static char bootup_trigger_buf[COMMAND_LINE_SIZE];
+static int boot_trigger_buf_len;
 static int nr_boot_triggers;
 
 static __init int setup_trace_triggers(char *str)
 {
 	char *trigger;
 	char *buf;
+	int len = boot_trigger_buf_len;
 	int i;
 
-	strscpy(bootup_trigger_buf, str, COMMAND_LINE_SIZE);
+	strscpy(bootup_trigger_buf + len , str, COMMAND_LINE_SIZE - len);
 	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 = bootup_trigger_buf + len;
+	boot_trigger_buf_len += strlen(buf);
+
+	for (i = nr_boot_triggers; i < MAX_BOOT_TRIGGERS; i++) {
 		trigger = strsep(&buf, ",");
 		if (!trigger)
 			break;