[PATCH v7 1/2] tracing: Append repeated boot-time tracing parameters

Wesley Atwell
2026-03-30T18:11:15Z

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.

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@gmail.com>
---
Changes since v6: https://lore.kernel.org/all/20260329184254.1813273-1-atwellwea@gmail.com/
- split trace_trigger= handling into a separate patch
- add the requested blank line in trace_append_boot_param()
---
kernel/trace/ftrace.c | 12 ++++++++----
kernel/trace/trace.c | 31 ++++++++++++++++++++++++++++++-
kernel/trace/trace.h | 2 ++
kernel/trace/trace_kprobe.c | 3 ++-
4 files changed, 42 insertions(+), 6 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..652d9f4e7943 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -228,6 +228,34 @@ 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;
+
+ /* 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 +357,8 @@ 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..1579cdec3f56 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -862,6 +862,8 @@ extern int DYN_FTRACE_TEST_NAME(void);
#define DYN_FTRACE_TEST_NAME2 trace_selftest_dynamic_test_func2
extern int DYN_FTRACE_TEST_NAME2(void);

+void __init trace_append_boot_param(char *buf, const char *str,
+ char sep, int size);
extern void trace_set_ring_buffer_expanded(struct trace_array *tr);
extern bool tracing_selftest_disabled;

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;

base-commit: e3c33bc767b5512dbfec643a02abf58ce608f3b2
--
2.43.0