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SubjectRe: [PATCH v9 20/22] tracing: Remove restriction on string position in hist trigger keys
On Thu, Jul 16, 2015 at 12:22:53PM -0500, Tom Zanussi wrote:
> If we assume the maximum size for a string field, we don't have to
> worry about its position. Since we only allow two keys in a compound
> key and having more than one string key in a given compound key
> doesn't make much sense anyway, trading a bit of extra space instead
> of introducing an arbitrary restriction makes more sense.
>
> We also need to use the event field size for static strings when
> copying the contents, otherwise we get random garbage in the key.
>
> Finally, rearrange the code without changing any functionality by
> moving the compound key updating code into a separate function.
>
> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>

Looks good to me. Just a nitpick below..


> ---
> kernel/trace/trace_events_hist.c | 65 +++++++++++++++++++++++-----------------
> 1 file changed, 37 insertions(+), 28 deletions(-)
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 67fffee..4ba7645 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -508,8 +508,8 @@ static int create_key_field(struct hist_trigger_data *hist_data,
> goto out;
> }
>
> - if (is_string_field(field)) /* should be last key field */
> - key_size = HIST_KEY_SIZE_MAX - key_offset;
> + if (is_string_field(field))
> + key_size = MAX_FILTER_STR_VAL;
> else
> key_size = field->size;
> }
> @@ -781,9 +781,36 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
> }
> }
>
> +static inline void add_to_key(char *compound_key, void *key,
> + struct hist_field *key_field, void *rec)
> +{
> + size_t size = key_field->size;
> +
> + if (key_field->flags & HIST_FIELD_STRING) {
> + struct ftrace_event_field *field;
> +
> + /* ensure NULL-termination */
> + size--;

This is unnecessary since the size value will be updated below anyway.
I think it's enough just to move the comment to ...


> +
> + 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);
> + else if (field->filter_type == FILTER_STATIC_STRING)
> + size = field->size;
> +

... here. :)

> + if (size > key_field->size - 1)
> + size = key_field->size - 1;
> + }
> +
> + memcpy(compound_key + key_field->offset, key, size);
> +}
> +
> static void event_hist_trigger(struct event_trigger_data *data, void *rec)
> {
> struct hist_trigger_data *hist_data = data->private_data;
> + bool use_compound_key = (hist_data->n_keys > 1);
> unsigned long entries[HIST_STACKTRACE_DEPTH];
> char compound_key[HIST_KEY_SIZE_MAX];
> struct stack_trace stacktrace;
> @@ -798,8 +825,7 @@ static void event_hist_trigger(struct event_trigger_data *data, void *rec)
> return;
> }
>
> - if (hist_data->n_keys > 1)
> - memset(compound_key, 0, hist_data->key_size);
> + memset(compound_key, 0, hist_data->key_size);
>
> for (i = hist_data->n_vals; i < hist_data->n_fields; i++) {
> key_field = hist_data->fields[i];
> @@ -816,35 +842,18 @@ static void event_hist_trigger(struct event_trigger_data *data, void *rec)
> key = entries;
> } else {
> field_contents = key_field->fn(key_field, rec);
> - if (key_field->flags & HIST_FIELD_STRING)
> + if (key_field->flags & HIST_FIELD_STRING) {
> key = (void *)field_contents;
> - else
> + use_compound_key = true;
> + } else
> 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,
> - size);
> - }
> }
> +
> + if (use_compound_key)
> + add_to_key(compound_key, key, key_field, rec);
> }
>
> - if (hist_data->n_keys > 1)
> + if (use_compound_key)
> key = compound_key;
>
> elt = tracing_map_insert(hist_data->map, key);
> --
> 1.9.3
>


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