Re: [PATCH v9 20/22] tracing: Remove restriction on string position in hist trigger keys

[Namhyung Kim <namhyung@kernel.org>]

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
>