Hi Namhyung,

On Fri, 2017-12-08 at 22:06 +0900, Namhyung Kim wrote:

On Wed, Dec 06, 2017 at 04:38:00PM -0600, Tom Zanussi wrote:

quoted

Up until now, hist triggers only needed per-element support for saving
'comm' data, which was saved directly as a private data pointer.

In anticipation of the need to save other data besides 'comm', add a
new hist_elt_data struct for the purpose, and switch the current
'comm'-related code over to that.

Signed-off-by: Tom Zanussi <redacted>
---
 kernel/trace/trace_events_hist.c | 76 +++++++++++++++++++++++-----------------
 1 file changed, 43 insertions(+), 33 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index f75f7bc..3aeab8e 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c

@@ -289,6 +289,10 @@ static struct hist_field *find_var(struct hist_trigger_data *hist_data,
 	return NULL;
 }
 
+struct hist_elt_data {
+	char *comm;
+};
+
 static const char *hist_field_name(struct hist_field *field,
 				   unsigned int level)
 {

@@ -503,45 +507,61 @@ static inline void save_comm(char *comm, struct task_struct *task)
 	memcpy(comm, task->comm, TASK_COMM_LEN);
 }
 
-static void hist_trigger_elt_comm_free(struct tracing_map_elt *elt)
+static void hist_elt_data_free(struct hist_elt_data *elt_data)
+{
+	kfree(elt_data->comm);
+	kfree(elt_data);
+}
+
+static void hist_trigger_elt_data_free(struct tracing_map_elt *elt)
 {
-	kfree((char *)elt->private_data);
+	struct hist_elt_data *elt_data = elt->private_data;
+
+	hist_elt_data_free(elt_data);
 }
 
-static int hist_trigger_elt_comm_alloc(struct tracing_map_elt *elt)
+static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
 {
 	struct hist_trigger_data *hist_data = elt->map->private_data;
+	unsigned int size = TASK_COMM_LEN + 1;

AFAIK you don't need to do '+ 1' since task->comm is always terminated
by a NUL character using strlcpy().

Good point, will change.

Thanks,

Tom