Re: [RFC PATCH] libtraceevent: Add tep_print_selected_fields()

[Yordan Karadzhov <y.karadz@gmail.com>]

Steven,

The implementation of static void tep_print_fmt_field() is incomplete.
If you compare the logic there with the implementation of
void tep_print_field() you will see that I am not handling the case of
a field that is an "ARRAY".

Any ideas what is the best way to handle this case?

Thanks!
Yordan


On 2.08.21 г. 14:27, Yordan Karadzhov (VMware) wrote:
> The new method can print only a subset of the unique data fields of
> the trace event. The print format is derived from the parsing tokens
> (tep_print_parse objects) of the event. As a byproduct of this change
> the existing method tep_print_fields() gets upgraded to use the
> formats provided by the tokens.
> 
> Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
> ---
>   src/event-parse.c | 87 ++++++++++++++++++++++++++++++++++++++++++-----
>   src/event-parse.h |  3 ++
>   2 files changed, 81 insertions(+), 9 deletions(-)
> 
> diff --git a/src/event-parse.c b/src/event-parse.c
> index f42ae38..7302f3d 100644
> --- a/src/event-parse.c
> +++ b/src/event-parse.c
> @@ -3585,6 +3585,8 @@ tep_find_field(struct tep_event *event, const char *name)
>   	return format;
>   }
>   
> +
> +
>   /**
>    * tep_find_any_field - find any field by name
>    * @event: handle for the event
> @@ -5333,6 +5335,19 @@ static int is_printable_array(char *p, unsigned int len)
>   	return 1;
>   }
>   
> +static void dynamic_offset(struct tep_handle *tep,
> +			   struct tep_format_field *field,
> +			   void *data,
> +			   unsigned int *offset,
> +			   unsigned int *len)
> +{
> +	unsigned long long val;
> +
> +	val = tep_read_number(tep, data + field->offset, field->size);
> +	*offset = val & SHRT_MAX;
> +	*len = val >> 16;
> +}
> +
>   void tep_print_field(struct trace_seq *s, void *data,
>   		     struct tep_format_field *field)
>   {
> @@ -5343,12 +5358,9 @@ void tep_print_field(struct trace_seq *s, void *data,
>   	if (field->flags & TEP_FIELD_IS_ARRAY) {
>   		offset = field->offset;
>   		len = field->size;
> -		if (field->flags & TEP_FIELD_IS_DYNAMIC) {
> -			val = tep_read_number(tep, data + offset, len);
> -			offset = val;
> -			len = offset >> 16;
> -			offset &= 0xffff;
> -		}
> +		if (field->flags & TEP_FIELD_IS_DYNAMIC)
> +			dynamic_offset(tep, field, data, &offset, &len);
> +
>   		if (field->flags & TEP_FIELD_IS_STRING &&
>   		    is_printable_array(data + offset, len)) {
>   			trace_seq_printf(s, "%s", (char *)data + offset);
> @@ -5398,19 +5410,76 @@ void tep_print_field(struct trace_seq *s, void *data,
>   	}
>   }
>   
> -void tep_print_fields(struct trace_seq *s, void *data,
> -		      int size __maybe_unused, struct tep_event *event)
> +static struct tep_print_parse *parse_format_next(struct tep_print_parse *parse)
> +{
> +	while (parse) {
> +		if (strncmp(parse->format, "%", 1) == 0)
> +			break;
> +
> +		parse = parse->next;
> +	}
> +
> +	return parse;
> +}
> +
> +static void tep_print_fmt_field(struct trace_seq *s, void *data,
> +				const char *format,
> +				struct tep_format_field *field)
> +{
> +	struct tep_handle *tep = field->event->tep;
> +	unsigned int len, offset;
> +	unsigned long long val;
> +
> +	if (field->flags & TEP_FIELD_IS_DYNAMIC) {
> +		dynamic_offset(tep, field, data, &offset, &len);
> +		if (len)
> +			trace_seq_printf(s, format, (char *)data + offset);
> +		else
> +			trace_seq_printf(s, format, "(nil)");
> +	} else {
> +		val = tep_read_number(tep, data + field->offset, field->size);
> +		trace_seq_printf(s, format, val);
> +	}
> +}
> +
> +void tep_print_selected_fields(struct trace_seq *s, void *data,
> +			       struct tep_event *event,
> +			       int ignore_mask)
>   {
>   	struct tep_format_field *field;
> +	struct tep_print_parse *parse;
> +	unsigned int len;
> +	int field_mask = 1;
>   
> +	parse = event->print_fmt.print_cache;
>   	field = event->format.fields;
>   	while (field) {
> +		parse = parse_format_next(parse);
> +
> +		if (field_mask & ignore_mask)
> +			goto next;
> +
>   		trace_seq_printf(s, " %s=", field->name);
> -		tep_print_field(s, data, field);
> +
> +		len = strlen(parse->format);
> +		if (len > 0 && parse->format[len - 1] == 'x')
> +			trace_seq_printf(s, "0x");
> +
> +		tep_print_fmt_field(s, data, parse->format, field);
> +
> + next:
>   		field = field->next;
> +		parse = parse->next;
> +		field_mask *= 2;
>   	}
>   }
>   
> +void tep_print_fields(struct trace_seq *s, void *data,
> +		      int size __maybe_unused, struct tep_event *event)
> +{
> +	tep_print_selected_fields(s, data, event, 0);
> +}
> +
>   static int print_function(struct trace_seq *s, const char *format,
>   			  void *data, int size, struct tep_event *event,
>   			  struct tep_print_arg *arg)
> diff --git a/src/event-parse.h b/src/event-parse.h
> index d4a876f..fe0fbf4 100644
> --- a/src/event-parse.h
> +++ b/src/event-parse.h
> @@ -547,6 +547,9 @@ void tep_print_field(struct trace_seq *s, void *data,
>   		     struct tep_format_field *field);
>   void tep_print_fields(struct trace_seq *s, void *data,
>   		      int size __maybe_unused, struct tep_event *event);
> +void tep_print_selected_fields(struct trace_seq *s, void *data,
> +			       struct tep_event *event,
> +			       int ignore_mask);
>   int tep_strerror(struct tep_handle *tep, enum tep_errno errnum,
>   		 char *buf, size_t buflen);
>   
>