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tracing: Support string type key properly
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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

Link: http://lkml.kernel.org/r/610180d6df0cfdf11ee205452f3b241dea657233.1457029949.git.tom.zanussi@linux.intel.com

Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
[ Added (unsigned long) typecast to fix compile warning ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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namhyung authored and rostedt committed Apr 19, 2016
1 parent 69a0200 commit 79e577c
Showing 1 changed file with 45 additions and 4 deletions.
49 changes: 45 additions & 4 deletions kernel/trace/trace_events_hist.c
Original file line number Diff line number Diff line change
Expand Up @@ -52,12 +52,28 @@ 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)(unsigned long)addr;
}

static u64 hist_field_pstring(struct hist_field *hist_field, void *event)
{
char **addr = (char **)(event + hist_field->field->offset);

return (u64)(unsigned long)*addr;
}

#define DEFINE_HIST_FIELD_FN(type) \
static u64 hist_field_##type(struct hist_field *hist_field, void *event)\
{ \
type *addr = (type *)(event + hist_field->field->offset); \
\
return (u64)*addr; \
return (u64)(unsigned long)*addr; \
}

DEFINE_HIST_FIELD_FN(s64);
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
}
}
}
Expand Down

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