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

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

On 2.08.21 г. 19:29, Steven Rostedt wrote:
> What I was talking about is to change tep_print_field() to do something like:
> 
> Take the current tep_print_field() and turn it into static _tep_print_field().
> 
>   [ Not even compiled tested ]
> 

Hi Steven,

I am not able to make sense from the code below.

> void tep_print_field(struct trace_seq *s, void *data,
> 		     struct tep_format_field *field)
> {
> 	struct tep_event = field->event;
> 	struct tep_print_parse = event->print_fmt.print_cache;
> 	struct tep_handle *tep = event->tep;
> 	unsigned int offset, len;
> 
> 	if (event->flags & TEP_EVENT_FL_FAILED)
> 		goto out;
> 
> 	if (field->flags & TEP_FIELD_IS_DYNAMIC)
> 		dynamic_offset(tep, field, data, &offset, &len);
> 
> 	for (;parse; parse = parse->next) {

You need
         if (!parse->arg)
			continue;

> 		if (parse->type == PRINT_FMT_STRING)
> 			continue;
> 		if (parse->arg->type != TEP_PRINT_FIELD)
> 			continue;

I can't understand the idea of those two checks. I printed the values and they don't seem to have any selective power.

> 		if (parse->arg->field.field->field != field)
> 			continue;
> 

This does not compile. I guess you mean
  		if (parse->arg->field.field != field)
  			continue;

however "parse->arg->field.field" looks like unused memory (NULL or 0xffffffff) and this check always fails.

Maybe we must call some of the process_XXX()static functions first in order to make your new version of 
tep_print_field() works?

Thanks!
Yordan

> 		print_parse_data(parse, s, data, size, event);
> 		return;
> 	}
> 
>   out:
> 	/* Not found */
>