perf ftrace: Use process/session specific trace settings

Executing 'perf ftrace' commands 'ftrace', 'profile' and 'latency' leave
tracing disabled as can seen in this output:

 # echo 1 > /sys/kernel/debug/tracing/tracing_on
 # cat /sys/kernel/debug/tracing/tracing_on
 1
 # perf ftrace trace --graph-opts depth=5 sleep 0.1 > /dev/null
 # cat /sys/kernel/debug/tracing/tracing_on
 0
 #

The 'tracing_on' file is not restored to its value before the command.

To fix that this patch uses the .../tracing/instances/XXX subdirectory
feature.

Each 'perf ftrace' invocation creates its own session/process
specific subdirectory and does not change the global state
in the .../tracing directory itself.

Use rmdir(../tracing/instances/dir) to stop process/session specific
tracing and delete all process/session specific setings.

Reported-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Suggested-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: https://lore.kernel.org/r/20250520093726.2009696-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: Thomas Richter

tools/perf/builtin-ftrace.c

@@ -19,6 +19,7 @@
 #include <ctype.h>
 #include <linux/capability.h>
 #include <linux/string.h>
+#include <sys/stat.h>
 
 #include "debug.h"
 #include <subcmd/pager.h>
@@ -45,6 +46,8 @@ static volatile sig_atomic_t done;
 
 static struct stats latency_stats;  /* for tracepoints */
 
+static char tracing_instance[PATH_MAX];	/* Trace instance directory */
+
 static void sig_handler(int sig __maybe_unused)
 {
 	done = true;
@@ -100,6 +103,34 @@ static bool is_ftrace_supported(void)
 	return supported;
 }
 
+/*
+ * Wrapper to test if a file in directory .../tracing/instances/XXX
+ * exists. If so return the .../tracing/instances/XXX file for use.
+ * Otherwise the file exists only in directory .../tracing and
+ * is applicable to all instances, for example file available_filter_functions.
+ * Return that file name in this case.
+ *
+ * This functions works similar to get_tracing_file() and expects its caller
+ * to free the returned file name.
+ *
+ * The global variable tracing_instance is set in init_tracing_instance()
+ * called at the  beginning to a process specific tracing subdirectory.
+ */
+static char *get_tracing_instance_file(const char *name)
+{
+	char *file;
+
+	if (asprintf(&file, "%s/%s", tracing_instance, name) < 0)
+		return NULL;
+
+	if (!access(file, F_OK))
+		return file;
+
+	free(file);
+	file = get_tracing_file(name);
+	return file;
+}
+
 static int __write_tracing_file(const char *name, const char *val, bool append)
 {
 	char *file;
@@ -109,7 +140,7 @@ static int __write_tracing_file(const char *name, const char *val, bool append)
 	char errbuf[512];
 	char *val_copy;
 
-	file = get_tracing_file(name);
+	file = get_tracing_instance_file(name);
 	if (!file) {
 		pr_debug("cannot get tracing file: %s\n", name);
 		return -1;
@@ -167,7 +198,7 @@ static int read_tracing_file_to_stdout(const char *name)
 	int fd;
 	int ret = -1;
 
-	file = get_tracing_file(name);
+	file = get_tracing_instance_file(name);
 	if (!file) {
 		pr_debug("cannot get tracing file: %s\n", name);
 		return -1;
@@ -209,7 +240,7 @@ static int read_tracing_file_by_line(const char *name,
 	char *file;
 	FILE *fp;
 
-	file = get_tracing_file(name);
+	file = get_tracing_instance_file(name);
 	if (!file) {
 		pr_debug("cannot get tracing file: %s\n", name);
 		return -1;
@@ -299,6 +330,39 @@ static int reset_tracing_files(struct perf_ftrace *ftrace __maybe_unused)
 	return 0;
 }
 
+/* Remove .../tracing/instances/XXX subdirectory created with
+ * init_tracing_instance().
+ */
+static void exit_tracing_instance(void)
+{
+	if (rmdir(tracing_instance))
+		pr_err("failed to delete tracing/instances directory\n");
+}
+
+/* Create subdirectory within .../tracing/instances/XXX to have session
+ * or process specific setup. To delete this setup, simply remove the
+ * subdirectory.
+ */
+static int init_tracing_instance(void)
+{
+	char dirname[] = "instances/perf-ftrace-XXXXXX";
+	char *path;
+
+	path = get_tracing_file(dirname);
+	if (!path)
+		goto error;
+	strncpy(tracing_instance, path, sizeof(tracing_instance) - 1);
+	put_tracing_file(path);
+	path = mkdtemp(tracing_instance);
+	if (!path)
+		goto error;
+	return 0;
+
+error:
+	pr_err("failed to create tracing/instances directory\n");
+	return -1;
+}
+
 static int set_tracing_pid(struct perf_ftrace *ftrace)
 {
 	int i;
@@ -629,14 +693,17 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace)
 
 	select_tracer(ftrace);
 
+	if (init_tracing_instance() < 0)
+		goto out;
+
 	if (reset_tracing_files(ftrace) < 0) {
 		pr_err("failed to reset ftrace\n");
-		goto out;
+		goto out_reset;
 	}
 
 	/* reset ftrace buffer */
 	if (write_tracing_file("trace", "0") < 0)
-		goto out;
+		goto out_reset;
 
 	if (set_tracing_options(ftrace) < 0)
 		goto out_reset;
@@ -648,7 +715,7 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace)
 
 	setup_pager();
 
-	trace_file = get_tracing_file("trace_pipe");
+	trace_file = get_tracing_instance_file("trace_pipe");
 	if (!trace_file) {
 		pr_err("failed to open trace_pipe\n");
 		goto out_reset;
@@ -723,7 +790,7 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace)
 out_close_fd:
 	close(trace_fd);
 out_reset:
-	reset_tracing_files(ftrace);
+	exit_tracing_instance();
 out:
 	return (done && !workload_exec_errno) ? 0 : -1;
 }
@@ -924,6 +991,9 @@ static int prepare_func_latency(struct perf_ftrace *ftrace)
 	if (ftrace->target.use_bpf)
 		return perf_ftrace__latency_prepare_bpf(ftrace);
 
+	if (init_tracing_instance() < 0)
+		return -1;
+
 	if (reset_tracing_files(ftrace) < 0) {
 		pr_err("failed to reset ftrace\n");
 		return -1;
@@ -942,7 +1012,7 @@ static int prepare_func_latency(struct perf_ftrace *ftrace)
 		return -1;
 	}
 
-	trace_file = get_tracing_file("trace_pipe");
+	trace_file = get_tracing_instance_file("trace_pipe");
 	if (!trace_file) {
 		pr_err("failed to open trace_pipe\n");
 		return -1;
@@ -993,7 +1063,7 @@ static int cleanup_func_latency(struct perf_ftrace *ftrace)
 	if (ftrace->target.use_bpf)
 		return perf_ftrace__latency_cleanup_bpf(ftrace);
 
-	reset_tracing_files(ftrace);
+	exit_tracing_instance();
 	return 0;
 }
 
@@ -1304,17 +1374,20 @@ static int __cmd_profile(struct perf_ftrace *ftrace)
 		goto out;
 	}
 
+	if (init_tracing_instance() < 0)
+		goto out;
+
 	if (reset_tracing_files(ftrace) < 0) {
 		pr_err("failed to reset ftrace\n");
-		goto out;
+		goto out_reset;
 	}
 
 	/* reset ftrace buffer */
 	if (write_tracing_file("trace", "0") < 0)
-		goto out;
+		goto out_reset;
 
 	if (set_tracing_options(ftrace) < 0)
-		return -1;
+		goto out_reset;
 
 	if (write_tracing_file("current_tracer", ftrace->tracer) < 0) {
 		pr_err("failed to set current_tracer to %s\n", ftrace->tracer);
@@ -1323,7 +1396,7 @@ static int __cmd_profile(struct perf_ftrace *ftrace)
 
 	setup_pager();
 
-	trace_file = get_tracing_file("trace_pipe");
+	trace_file = get_tracing_instance_file("trace_pipe");
 	if (!trace_file) {
 		pr_err("failed to open trace_pipe\n");
 		goto out_reset;
@@ -1385,7 +1458,7 @@ static int __cmd_profile(struct perf_ftrace *ftrace)
 out_close_fd:
 	close(trace_fd);
 out_reset:
-	reset_tracing_files(ftrace);
+	exit_tracing_instance();
 out:
 	return (done && !workload_exec_errno) ? 0 : -1;
 }