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Subject[PATCH 2/4] ftrace: Add 'function-fork' trace option
Date
The function-fork option is same as event-fork that it tracks task
fork/exit and set the pid filter properly. This can be useful if user
wants to trace selected tasks including their children only.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
kernel/trace/ftrace.c | 37 +++++++++++++++++++++++++++++++++++++
kernel/trace/trace.c | 5 ++++-
kernel/trace/trace.h | 6 +++++-
3 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index b451a860e885..7ca2ed8d0a48 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5575,6 +5575,43 @@ ftrace_filter_pid_sched_switch_probe(void *data, bool preempt,
trace_ignore_this_task(pid_list, next));
}

+static void
+ftrace_pid_follow_sched_process_fork(void *data,
+ struct task_struct *self,
+ struct task_struct *task)
+{
+ struct trace_pid_list *pid_list;
+ struct trace_array *tr = data;
+
+ pid_list = rcu_dereference_sched(tr->function_pids);
+ trace_filter_add_remove_task(pid_list, self, task);
+}
+
+static void
+ftrace_pid_follow_sched_process_exit(void *data, struct task_struct *task)
+{
+ struct trace_pid_list *pid_list;
+ struct trace_array *tr = data;
+
+ pid_list = rcu_dereference_sched(tr->function_pids);
+ trace_filter_add_remove_task(pid_list, NULL, task);
+}
+
+void ftrace_pid_follow_fork(struct trace_array *tr, bool enable)
+{
+ if (enable) {
+ register_trace_sched_process_fork(ftrace_pid_follow_sched_process_fork,
+ tr);
+ register_trace_sched_process_exit(ftrace_pid_follow_sched_process_exit,
+ tr);
+ } else {
+ unregister_trace_sched_process_fork(ftrace_pid_follow_sched_process_fork,
+ tr);
+ unregister_trace_sched_process_exit(ftrace_pid_follow_sched_process_exit,
+ tr);
+ }
+}
+
static void clear_ftrace_pids(struct trace_array *tr)
{
struct trace_pid_list *pid_list;
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b92489dfa829..291d8fc9dc36 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -257,7 +257,7 @@ unsigned long long ns2usecs(u64 nsec)

/* trace_flags that are default zero for instances */
#define ZEROED_TRACE_FLAGS \
- TRACE_ITER_EVENT_FORK
+ (TRACE_ITER_EVENT_FORK | TRACE_ITER_FUNC_FORK)

/*
* The global_trace is the descriptor that holds the top-level tracing
@@ -4205,6 +4205,9 @@ int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
if (mask == TRACE_ITER_EVENT_FORK)
trace_event_follow_fork(tr, enabled);

+ if (mask == TRACE_ITER_FUNC_FORK)
+ ftrace_pid_follow_fork(tr, enabled);
+
if (mask == TRACE_ITER_OVERWRITE) {
ring_buffer_change_overwrite(tr->trace_buffer.buffer, enabled);
#ifdef CONFIG_TRACER_MAX_TRACE
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 4d9804fd9a2d..bacf5e845c55 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -898,6 +898,7 @@ void ftrace_init_tracefs_toplevel(struct trace_array *tr,
struct dentry *d_tracer);
int init_function_trace(void);
void ftrace_pid_reset(struct trace_array *tr, bool update);
+void ftrace_pid_follow_fork(struct trace_array *tr, bool enable);
#else
static inline int ftrace_trace_task(struct trace_array *tr)
{
@@ -918,6 +919,7 @@ static inline void ftrace_init_tracefs(struct trace_array *tr, struct dentry *d)
static inline void ftrace_init_tracefs_toplevel(struct trace_array *tr, struct dentry *d) { }
static inline int init_function_trace(void) { return 0; }
static inline void ftrace_pid_reset(struct trace_array *tr, bool update) { }
+static inline void ftrace_pid_follow_fork(struct trace_array *tr, bool enable) { }
/* ftace_func_t type is not defined, use macro instead of static inline */
#define ftrace_init_array_ops(tr, func) do { } while (0)
#endif /* CONFIG_FUNCTION_TRACER */
@@ -991,11 +993,13 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf,

#ifdef CONFIG_FUNCTION_TRACER
# define FUNCTION_FLAGS \
- C(FUNCTION, "function-trace"),
+ C(FUNCTION, "function-trace"), \
+ C(FUNC_FORK, "function-fork"),
# define FUNCTION_DEFAULT_FLAGS TRACE_ITER_FUNCTION
#else
# define FUNCTION_FLAGS
# define FUNCTION_DEFAULT_FLAGS 0UL
+# define TRACE_ITER_FUNC_FORK 0UL
#endif

#ifdef CONFIG_STACKTRACE
--
2.12.0
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