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Subject[PATCH] tracing/filters: allow event filters to be set only when not tracing
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This patch adds code allowing the event filter to be set only if there's
no active tracing going on.

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>

---
kernel/trace/trace.c | 13 +++++++++++++
kernel/trace/trace.h | 2 ++
kernel/trace/trace_events.c | 7 +++++++
kernel/trace/trace_events_filter.c | 12 ++++++++++++
4 files changed, 34 insertions(+), 0 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3624b25..30530f7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -235,6 +235,19 @@ static struct tracer *trace_types __read_mostly;
/* current_trace points to the tracer that is currently active */
static struct tracer *current_trace __read_mostly;

+/**
+ * tracer_is_nop - return if nop tracer is current tracer
+ *
+ * This function is used by other tracers to know whether there is
+ * currently a tracer set. Tracers may use this function to know if
+ * it should enable their features when starting up. See event tracer
+ * for an example (event_filter_write).
+ */
+int tracer_is_nop(void)
+{
+ return current_trace == &nop_trace;
+}
+
/*
* max_tracer_type_len is used to simplify the allocating of
* buffers to read userspace tracer names. We keep track of
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index cfb07ef..6834345 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -466,6 +466,7 @@ struct trace_iterator {

int tracer_init(struct tracer *t, struct trace_array *tr);
int tracing_is_enabled(void);
+int tracer_is_nop(void);
void trace_wake_up(void);
void tracing_reset(struct trace_array *tr, int cpu);
void tracing_reset_online_cpus(struct trace_array *tr);
@@ -859,6 +860,7 @@ extern int filter_match_preds(struct ftrace_event_call *call, void *rec);
extern void filter_free_subsystem_preds(struct event_subsystem *system);
extern int filter_add_subsystem_pred(struct event_subsystem *system,
struct filter_pred *pred);
+extern int subsystem_events_enabled(struct event_subsystem *system);

static inline void
filter_check_discard(struct ftrace_event_call *call, void *rec,
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index be9299a..eb1d363 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -498,6 +498,9 @@ event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
struct filter_pred *pred;
int err;

+ if (tracing_is_enabled() && (!tracer_is_nop() || call->enabled))
+ return -EBUSY;
+
if (cnt >= sizeof(buf))
return -EINVAL;

@@ -564,6 +567,10 @@ subsystem_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
struct filter_pred *pred;
int err;

+ if (tracing_is_enabled() &&
+ (!tracer_is_nop() || subsystem_events_enabled(system)))
+ return -EBUSY;
+
if (cnt >= sizeof(buf))
return -EINVAL;

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 470ad94..a706e0b 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -172,6 +172,18 @@ void filter_free_preds(struct ftrace_event_call *call)
}
}

+int subsystem_events_enabled(struct event_subsystem *system)
+{
+ struct ftrace_event_call *call = __start_ftrace_events;
+
+ events_for_each(call) {
+ if (!strcmp(call->system, system->name) && call->enabled)
+ return 1;
+ }
+
+ return 0;
+}
+
void filter_free_subsystem_preds(struct event_subsystem *system)
{
struct ftrace_event_call *call = __start_ftrace_events;
--
1.5.6.3




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