[PATCH v14 13/22] tracing: Support string type key properly

From: Tom Zanussi
Date: Wed Feb 24 2016 - 13:38:45 EST


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 c20d8e0..277aa57 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);
@@ -504,7 +526,10 @@ 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);
@@ -835,8 +860,24 @@ 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