Re: [PATCH 5/5] tracing: New functions for kernel access to Ftrace instances

[Divya Indi]

Hi Steven,

Please find my comments inline -

On 10/15/19 4:19 PM, Steven Rostedt wrote:

On Wed, 14 Aug 2019 10:55:27 -0700
Divya Indi <divya.i...@oracle.com> wrote:

Adding 2 new functions -
1) trace_array_lookup : Look up and return a trace array, given its
name.
2) trace_array_set_clr_event : Enable/disable event recording to the
given trace array.

NOTE: trace_array_lookup returns a trace array and also increments the
reference counter associated with the returned trace array. Make sure to
call trace_array_put() once the use is done so that the instance can be
removed at a later time.

Example use:

tr = trace_array_lookup("foo-bar");

Should probably be renamed to: trace_array_get_by_name("foo-bar")

As the name should show that it adds a ref count.

Makes sense! Will make this change.

But if we make the change I suggested before, where we do not need to
do the put before calling the destroy, we should have:

if (!tr)

{

        tr = trace_array_create("foo-bar");

        trace_array_get(tr);

This would need a corresponding trace_array_put(?).
Additionally, this would again traverse the list of instances, So I
went with incrementing the ref ctr inside the function.

}

// Log to tr
// Enable/disable events to tr
trace_array_set_clr_event(tr, _THIS_IP,"system","event",1);

What's with the __THIS_IP?

My bad! Maybe remnants from a trace_array_printk copy-paste.
Will correct this.

// Done using tr
trace_array_put(tr);
..

Also, use trace_array_set_clr_event to enable/disable events to a trace array.
So now we no longer need to have ftrace_set_clr_event as an exported
API.

Signed-off-by: Divya Indi <divya.i...@oracle.com>
---
  include/linux/trace.h        |  2 ++
  include/linux/trace_events.h |  3 ++-
  kernel/trace/trace.c         | 28 ++++++++++++++++++++++++++++
  kernel/trace/trace_events.c  | 23 ++++++++++++++++++++++-
  4 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/include/linux/trace.h b/include/linux/trace.h
index 2c782d5..05164bb 100644
--- a/include/linux/trace.h
+++ b/include/linux/trace.h
@@ -32,6 +32,8 @@ int trace_array_printk(struct trace_array *tr, unsigned long 
ip,
  struct trace_array *trace_array_create(const char *name);
  int trace_array_destroy(struct trace_array *tr);
  void trace_array_put(struct trace_array *tr);
+struct trace_array *trace_array_lookup(const char *name);
+
  #endif        /* CONFIG_TRACING */

#endif /* _LINUX_TRACE_H */

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 8a62731..05a7514 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -540,7 +540,8 @@ extern int trace_define_field(struct trace_event_call 
*call, const char *type,
  #define is_signed_type(type)  (((type)(-1)) < (type)1)

int trace_set_clr_event(const char *system, const char *event, int set);

-
+int trace_array_set_clr_event(struct trace_array *tr, const char *system,
+               const char *event, int set);
  /*
   * The double __builtin_constant_p is because gcc will give us an error
   * if we try to allocate the static variable to fmt if it is not a
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7b6a37a..e394d55 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8514,6 +8514,34 @@ static int instance_rmdir(const char *name)
        return ret;
  }

+/**

+ * trace_array_lookup - Lookup the trace array, given its name.
+ * @name: The name of the trace array to be looked up.
+ *
+ * Lookup and return the trace array associated with @name.
+ *
+ * NOTE: The reference counter associated with the returned trace array is
+ * incremented to ensure it is not freed when in use. Make sure to call
+ * "trace_array_put" for this trace array when its use is done.
+ */
+struct trace_array *trace_array_lookup(const char *name)
+{
+       struct trace_array *tr;
+
+       mutex_lock(&trace_types_lock);
+
+       list_for_each_entry(tr, &ftrace_trace_arrays, list) {
+               if (tr->name && strcmp(tr->name, name) == 0) {
+                       tr->ref++;
+                       mutex_unlock(&trace_types_lock);
+                       return tr;
+               }
+       }
+       mutex_unlock(&trace_types_lock);
+       return NULL;
+}
+EXPORT_SYMBOL_GPL(trace_array_lookup);
+
  static __init void create_trace_instances(struct dentry *d_tracer)
  {
        trace_instance_dir = tracefs_create_instance_dir("instances", d_tracer,
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 2621995..96dd997 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -834,7 +834,6 @@ static int ftrace_set_clr_event(struct trace_array *tr, 
char *buf, int set)

return ret;

  }
-EXPORT_SYMBOL_GPL(ftrace_set_clr_event);

/**

   * trace_set_clr_event - enable or disable an event
@@ -859,6 +858,28 @@ int trace_set_clr_event(const char *system, const char 
*event, int set)
  }
  EXPORT_SYMBOL_GPL(trace_set_clr_event);

+/**

+ * trace_array_set_clr_event - enable or disable an event for a trace array
+ * @system: system name to match (NULL for any system)
+ * @event: event name to match (NULL for all events, within system)
+ * @set: 1 to enable, 0 to disable

We probably should make this a boolean.

This would internally call ftrace_set_clr_event which would expect 0/1.
But I agree making it boolean would be more intuitive.

Thanks,
Divya

-- Steve

+ *
+ * This is a way for other parts of the kernel to enable or disable
+ * event recording to instances.
+ *
+ * Returns 0 on success, -EINVAL if the parameters do not match any
+ * registered events.
+ */
+int trace_array_set_clr_event(struct trace_array *tr, const char *system,
+               const char *event, int set)
+{
+       if (!tr)
+               return -ENOENT;
+
+       return __ftrace_set_clr_event(tr, NULL, system, event, set);
+}
+EXPORT_SYMBOL_GPL(trace_array_set_clr_event);
+
  /* 128 should be much more than enough */
  #define EVENT_BUF_SIZE                127