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

[Wesley Atwell <atwellwea@gmail.com>]

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@gmail.com>
---
v5:
- 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(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 413310912609..8bd3dd1d549c 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6841,7 +6841,8 @@ bool ftrace_filter_param __initdata;
 static int __init set_ftrace_notrace(char *str)
 {
 	ftrace_filter_param = true;
-	strscpy(ftrace_notrace_buf, str, FTRACE_FILTER_SIZE);
+	trace_append_boot_param(ftrace_notrace_buf, str, ',',
+				FTRACE_FILTER_SIZE);
 	return 1;
 }
 __setup("ftrace_notrace=", set_ftrace_notrace);
@@ -6849,7 +6850,8 @@ __setup("ftrace_notrace=", set_ftrace_notrace);
 static int __init set_ftrace_filter(char *str)
 {
 	ftrace_filter_param = true;
-	strscpy(ftrace_filter_buf, str, FTRACE_FILTER_SIZE);
+	trace_append_boot_param(ftrace_filter_buf, str, ',',
+				FTRACE_FILTER_SIZE);
 	return 1;
 }
 __setup("ftrace_filter=", set_ftrace_filter);
@@ -6861,14 +6863,16 @@ static int ftrace_graph_set_hash(struct ftrace_hash *hash, char *buffer);
 
 static int __init set_graph_function(char *str)
 {
-	strscpy(ftrace_graph_buf, str, FTRACE_FILTER_SIZE);
+	trace_append_boot_param(ftrace_graph_buf, str, ',',
+				FTRACE_FILTER_SIZE);
 	return 1;
 }
 __setup("ftrace_graph_filter=", set_graph_function);
 
 static int __init set_graph_notrace_function(char *str)
 {
-	strscpy(ftrace_graph_notrace_buf, str, FTRACE_FILTER_SIZE);
+	trace_append_boot_param(ftrace_graph_notrace_buf, str, ',',
+				FTRACE_FILTER_SIZE);
 	return 1;
 }
 __setup("ftrace_graph_notrace=", set_graph_notrace_function);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a626211ceb9a..c8cf45dc4152 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -228,6 +228,32 @@ 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;
+	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 +355,8 @@ 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..7f0bec4622f6 100644
--- 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;
+
+	/*
+	 * 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;
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index a5dbb72528e0..e9f1c55aea64 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -31,7 +31,8 @@ static char kprobe_boot_events_buf[COMMAND_LINE_SIZE] __initdata;
 
 static int __init set_kprobe_boot_events(char *str)
 {
-	strscpy(kprobe_boot_events_buf, str, COMMAND_LINE_SIZE);
+	trace_append_boot_param(kprobe_boot_events_buf, str, ';',
+				COMMAND_LINE_SIZE);
 	disable_tracing_selftest("running kprobe events");
 
 	return 1;
-- 
2.43.0