[PATCH v16 13/23] tracing: Support string type key properly

[Tom Zanussi]

From: Namhyung Kim <namhyung@xxxxxxxxxx>

The string in a trace event is usually recorded as dynamic array which
is variable length.  But current hist code only support fixed length
array so it cannot support most strings.

This patch fixes it by checking filter_type of the field and get
proper pointer with it.  With this, it can get a histogram of exec()
based on filenames like below:

  # cd /sys/kernel/tracing/events/sched/sched_process_exec
  # cat 'hist:key=filename' > trigger
  # ps
   PID TTY       TIME CMD
     1 ?     00:00:00 init
    29 ?     00:00:00 sh
    38 ?     00:00:00 ps
  # ls
  enable  filter  format  hist  id  trigger
  # cat hist
  # trigger info: hist:keys=filename:vals=hitcount:sort=hitcount:size=2048 [active]

  { filename: /usr/bin/ps                         } hitcount:          1
  { filename: /usr/bin/ls                         } hitcount:          1
  { filename: /usr/bin/cat                        } hitcount:          1

  Totals:
      Hits: 3
      Entries: 3
      Dropped: 0

Cc: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 47 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 21cae42..3a7daae 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -52,6 +52,22 @@ static u64 hist_field_string(struct hist_field *hist_field, void *event)
 	return (u64)(unsigned long)addr;
 }
 
+static u64 hist_field_dynstring(struct hist_field *hist_field, void *event)
+{
+	u32 str_item = *(u32 *)(event + hist_field->field->offset);
+	int str_loc = str_item & 0xffff;
+	char *addr = (char *)(event + str_loc);
+
+	return (u64)addr;
+}
+
+static u64 hist_field_pstring(struct hist_field *hist_field, void *event)
+{
+	char **addr = (char **)(event + hist_field->field->offset);
+
+	return (u64)*addr;
+}
+
 #define DEFINE_HIST_FIELD_FN(type)					\
 static u64 hist_field_##type(struct hist_field *hist_field, void *event)\
 {									\
@@ -340,7 +356,13 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
 
 	if (is_string_field(field)) {
 		flags |= HIST_FIELD_FL_STRING;
-		hist_field->fn = hist_field_string;
+
+		if (field->filter_type == FILTER_STATIC_STRING)
+			hist_field->fn = hist_field_string;
+		else if (field->filter_type == FILTER_DYN_STRING)
+			hist_field->fn = hist_field_dynstring;
+		else
+			hist_field->fn = hist_field_pstring;
 	} else {
 		hist_field->fn = select_value_fn(field->size,
 						 field->is_signed);
@@ -508,7 +530,10 @@ static int create_key_field(struct hist_trigger_data *hist_data,
 			goto out;
 		}
 
-		key_size = field->size;
+		if (is_string_field(field)) /* should be last key field */
+			key_size = HIST_KEY_SIZE_MAX - key_offset;
+		else
+			key_size = field->size;
 	}
 
 	hist_data->fields[key_idx] = create_hist_field(field, flags);
@@ -841,8 +866,24 @@ static void event_hist_trigger(struct event_trigger_data *data, void *rec)
 				key = (void *)&field_contents;
 
 			if (hist_data->n_keys > 1) {
+				/* ensure NULL-termination */
+				size_t size = key_field->size - 1;
+
+				if (key_field->flags & HIST_FIELD_FL_STRING) {
+					struct ftrace_event_field *field;
+
+					field = key_field->field;
+					if (field->filter_type == FILTER_DYN_STRING)
+						size = *(u32 *)(rec + field->offset) >> 16;
+					else if (field->filter_type == FILTER_PTR_STRING)
+						size = strlen(key);
+
+					if (size > key_field->size - 1)
+						size = key_field->size - 1;
+				}
+
 				memcpy(compound_key + key_field->offset, key,
-				       key_field->size);
+				       size);
 			}
 		}
 	}
-- 
1.9.3