[PATCH 2/2] trace-cmd reset: Add option to preserve specific dynamic events

One may want to preserve some of the dynamic events (e.g., kprobes)
during a trace-cmd reset. Thus, provide -k command line option for
trace-cmd reset to allow keeping specified events untouched during the
reset operation.

For example, it's possible to prevent kprobes & kretprobes from being
destroyed in trace-cmd reset with this patch:

    # Add kprobe and kretprobe for sys_open():
    $ echo 'p do_sys_open' > /sys/kernel/tracing/kprobe_events
    $ echo 1 > /sys/kernel/tracing/events/kprobes/p_do_sys_open_0/enable
    $ echo 'r do_sys_open' >> /sys/kernel/tracing/kprobe_events
    $ echo 1 > /sys/kernel/tracing/events/kprobes/r_do_sys_open_0/enable
    $ cat /sys/kernel/tracing/kprobe_events
    p:kprobes/p_do_sys_open_0 do_sys_open
    r128:kprobes/r_do_sys_open_0 do_sys_open

    # Issue reset, but keep kprobes and kretprobes ('-k all' would keep
    # all existing dynamic events):
    $ trace-cmd reset -k kprobe -k kretprobe
    $ cat /sys/kernel/tracing/kprobe_events
    p:kprobes/p_do_sys_open_0 do_sys_open
    r128:kprobes/r_do_sys_open_0 do_sys_open

    # Issue reset, but this time only keep kretprobes:
    $ trace-cmd reset -k kretprobe
    $ cat /sys/kernel/tracing/kprobe_events
    r128:kprobes/r_do_sys_open_0 do_sys_open

    # Don't preserve any dynamic event:
    $ trace-cmd reset
    $ cat /sys/kernel/tracing/kprobe_events
    $

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=219302
Signed-off-by: Metin Kaya <[email protected]>
---
 tracecmd/trace-record.c | 59 ++++++++++++++++++++++++++++++++++++-----
 tracecmd/trace-usage.c  |  5 +++-
 2 files changed, 57 insertions(+), 7 deletions(-)

diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index c695cd23..f80b386f 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -5399,11 +5399,15 @@ static void clear_error_log(void)
 		clear_instance_error_log(instance);
 }
 
-static void clear_all_dynamic_events(void)
+static void clear_all_dynamic_events(unsigned int exclude_types)
 {
-	/* Clear event probes first, as they may be attached to other dynamic event */
-	tracefs_dynevent_destroy_all(TRACEFS_DYNEVENT_EPROBE, true);
-	tracefs_dynevent_destroy_all(TRACEFS_DYNEVENT_ALL, true);
+	/*
+	 * Clear event probes first (if they are not excluded), as they may be
+	 * attached to other dynamic event.
+	 */
+	if (!(TRACEFS_DYNEVENT_EPROBE & exclude_types))
+		tracefs_dynevent_destroy_all(TRACEFS_DYNEVENT_EPROBE, true);
+	tracefs_dynevent_destroy_all(TRACEFS_DYNEVENT_ALL & ~exclude_types, true);
 }
 
 static void clear_func_filters(void)
@@ -6036,11 +6040,51 @@ void trace_restart(int argc, char **argv)
 	exit(0);
 }
 
+/**
+ * find_dynevent_type - Find string formatted dynamic event type
+ *			in "enum tracefs_dynevent_type".
+ *
+ * @type: Dynamic event type in string format.
+ *
+ * Returns an unsigned int value for the event specified in @type.
+ */
+static unsigned int find_dynevent_type(const char *type)
+{
+	/* WARN: Should be kept in sync with "enum tracefs_dynevent_type". */
+	if (!strcmp(type, "kprobe"))
+		return TRACEFS_DYNEVENT_KPROBE;
+	else if (!strcmp(type, "kretprobe"))
+		return TRACEFS_DYNEVENT_KRETPROBE;
+	else if (!strcmp(type, "uprobe"))
+		return TRACEFS_DYNEVENT_UPROBE;
+	else if (!strcmp(type, "uretprobe"))
+		return TRACEFS_DYNEVENT_URETPROBE;
+	else if (!strcmp(type, "eprobe"))
+		return TRACEFS_DYNEVENT_EPROBE;
+	else if (!strcmp(type, "synth"))
+		return TRACEFS_DYNEVENT_SYNTH;
+	else if (!strcmp(type, "all"))
+		/*
+		 * Unfortunately TRACEFS_DYNEVENT_ALL does not work here.
+		 * Because tracefs_dynevent_destroy_all() assumes 0 means all
+		 * and destroys all dynamic events.
+		 */
+		return (TRACEFS_DYNEVENT_KPROBE |
+			TRACEFS_DYNEVENT_KRETPROBE |
+			TRACEFS_DYNEVENT_UPROBE |
+			TRACEFS_DYNEVENT_URETPROBE |
+			TRACEFS_DYNEVENT_EPROBE |
+			TRACEFS_DYNEVENT_SYNTH);
+	else
+		die("Invalid event type '%s'!\n", type);
+}
+
 void trace_reset(int argc, char **argv)
 {
 	int c;
 	int topt = 0;
 	struct buffer_instance *instance = &top_instance;
+	unsigned int excluded_types = 0;
 
 	init_top_instance();
 
@@ -6048,7 +6092,7 @@ void trace_reset(int argc, char **argv)
 	int last_specified_all = 0;
 	struct buffer_instance *inst; /* iterator */
 
-	while ((c = getopt(argc-1, argv+1, "hab:B:td")) >= 0) {
+	while ((c = getopt(argc-1, argv+1, "hab:B:tdk:")) >= 0) {
 
 		switch (c) {
 		case 'h':
@@ -6102,6 +6146,9 @@ void trace_reset(int argc, char **argv)
 				instance->flags &= ~BUFFER_FL_KEEP;
 			}
 			break;
+		case 'k':
+			excluded_types |= find_dynevent_type(optarg);
+			break;
 		default:
 			usage(argv);
 			break;
@@ -6112,7 +6159,7 @@ void trace_reset(int argc, char **argv)
 	set_buffer_size();
 	clear_filters();
 	clear_triggers();
-	clear_all_dynamic_events();
+	clear_all_dynamic_events(excluded_types);
 	clear_error_log();
 	/* set clock to "local" */
 	reset_clock();
diff --git a/tracecmd/trace-usage.c b/tracecmd/trace-usage.c
index 8bbf2e3e..f159e5e1 100644
--- a/tracecmd/trace-usage.c
+++ b/tracecmd/trace-usage.c
@@ -193,7 +193,7 @@ static struct usage_help usage_help[] = {
 	{
 		"reset",
 		"disable all kernel tracing and clear the trace buffers",
-		" %s reset [-b size][-B buf][-a][-d][-t]\n"
+		" %s reset [-b size][-B buf][-k event][-a][-d][-t]\n"
 		"          Disables the tracer (may reset trace file)\n"
 		"          Used in conjunction with start\n"
 		"          -b change the kernel buffer size (in kilobytes per CPU)\n"
@@ -201,6 +201,9 @@ static struct usage_help usage_help[] = {
 		"          -B reset the given buffer instance (may specify multiple -B)\n"
 		"          -a reset all instances (except top one)\n"
 		"          -t reset the top level instance (useful with -B or -a)\n"
+		"          -k keep dynamic event during reset. Valid values are:\n"
+		"              'kprobe', 'kretprobe', 'uprobe', 'uretprobe',\n"
+		"              'eprobe', 'synth' and 'all'.\n"
 	},
 	{
 		"clear",
-- 
2.34.1