Re: [PATCH v7 00/10] tracing: 'hist' triggers

[Namhyung Kim <namhyung@kernel.org>]

Hi Tom,

I tried to play with this patchset, and it worked greatly.  Thanks for
your work!

But I found that it doesn't handle string fields properly so I can see
failure on accessing 'filename' field in sched_process_exec event.
Below is my fix for that..  Can you take a look at it?

Thanks,
Namhyung



>From e0442e9aec9740e4f20931ff10545f07c8d6d346 Mon Sep 17 00:00:00 2001
From: Namhyung Kim <namhyung@kernel.org>
Date: Thu, 11 Jun 2015 11:48:41 +0900
Subject: [PATCH] tracing: Support string type key properly

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@linux.intel.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 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 5ea18956497d..d5edf9fa5aea 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)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)\
 {									\
@@ -330,7 +346,13 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
 
 	if (is_string_field(field)) {
 		flags |= HIST_FIELD_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);
@@ -485,7 +507,10 @@ 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);
@@ -791,8 +816,24 @@ 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_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);
 			}
 		}
 	}
-- 
2.4.2