[PATCH v7 2/2] tracing: Preserve repeated trace_trigger boot parameters

[Wesley Atwell <atwellwea@gmail.com>]

trace_trigger= tokenizes bootup_trigger_buf in place and stores pointers
into that buffer for later trigger registration. Repeated trace_trigger=
parameters overwrite the buffer contents from earlier calls, leaving
only the last set of parsed event and trigger strings.

Keep each new trace_trigger= string at the end of bootup_trigger_buf and
parse only the appended range. That preserves the earlier event and
trigger strings while still letting repeated parameters queue additional
boot-time triggers.

This also lets Bootconfig array values work naturally when they expand
to repeated trace_trigger= entries.

Before this change, only the last trace_trigger= instance survived boot.

Signed-off-by: Wesley Atwell <atwellwea@gmail.com>
---
Changes since v6: https://lore.kernel.org/all/20260329184254.1813273-1-atwellwea@gmail.com/
- split trace_trigger= handling into its own patch
- follow Steven Rostedt's suggested bootup_trigger_buf offset approach
- account for the terminating NUL when advancing boot_trigger_buf_len
---
 kernel/trace/trace_events.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 249d1cba72c0..dd26e838d4de 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -3679,20 +3679,27 @@ 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);
+	if (len >= COMMAND_LINE_SIZE)
+		return 1;
+
+	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) + 1;
+
+	for (i = nr_boot_triggers; i < MAX_BOOT_TRIGGERS; i++) {
 		trigger = strsep(&buf, ",");
 		if (!trigger)
 			break;
-- 
2.43.0