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SubjectRe: [PATCH] tools/lib/traceevent, tools/perf: Move struct tep_handler definition in a local header file
Hi,

On 2019-07-26 09:12:00 -0400, Steven Rostedt wrote:
> On Thu, 25 Jul 2019 20:58:29 -0700
> Andres Freund <andres@anarazel.de> wrote:
> >
> > Is just plain wrong, as:
> >
> > > - return pevent->events[idx];
> > > + return (all_events + idx);
> >
> > that's not a valid conversion. ->events isn't an array of tep_handle,
> > it's an array of tep_handle* (and even if it were, the previous notation
>
> You're right, it is wrong, but it's not tep_handle* but
> tep_event_format*.

Err, yea. Typo.



> > diff --git i/tools/lib/traceevent/event-parse.h w/tools/lib/traceevent/event-parse.h
> > index 642f68ab5fb2..7ebc9b5308d4 100644
> > --- i/tools/lib/traceevent/event-parse.h
> > +++ w/tools/lib/traceevent/event-parse.h
> > @@ -517,6 +517,7 @@ int tep_read_number_field(struct tep_format_field *field, const void *data,
> > unsigned long long *value);
> >
> > struct tep_event *tep_get_first_event(struct tep_handle *tep);
> > +struct tep_event *tep_get_event(struct tep_handle *tep, int index);
>
> I was looking at the tep_get_event() code, and we should switch that to
> "unsigned int index" otherwise passing in a negative number will return
> an address outside the array.

Makes sense.


> > int tep_get_events_count(struct tep_handle *tep);
> > struct tep_event *tep_find_event(struct tep_handle *tep, int id);
> >
> > diff --git i/tools/perf/util/trace-event-parse.c w/tools/perf/util/trace-event-parse.c
> > index 62bc61155dd1..6a035ffd58ac 100644
> > --- i/tools/perf/util/trace-event-parse.c
> > +++ w/tools/perf/util/trace-event-parse.c
> > @@ -179,28 +179,26 @@ struct tep_event *trace_find_next_event(struct tep_handle *pevent,
> > {
> > static int idx;
> > int events_count;
> > - struct tep_event *all_events;
> >
> > - all_events = tep_get_first_event(pevent);
> > events_count = tep_get_events_count(pevent);
>
> I think we can get rid of the events_count and all its checks, as the
> same check is done within tep_get_event().

> > - if (!pevent || !all_events || events_count < 1)
> > + if (!pevent || events_count < 1)
>
> if (!pevent)
>
> > return NULL;
> >
> > if (!event) {
> > idx = 0;
> > - return all_events;
> > + return tep_get_event(pevent, 0);
> > }
> >
> > - if (idx < events_count && event == (all_events + idx)) {
> > + if (idx < events_count && event == tep_get_event(pevent, idx)) {
>
> if (event == tep_get_event(pevent, idx))
> return tep_get_event(pevent, ++idx);
>
> > idx++;
> > if (idx == events_count)
> > return NULL;
> > - return (all_events + idx);
> > + return tep_get_event(pevent, idx);
> > }
> >
>
> struct tep_event_format *next_event;
>
> for (idx = 0; next_event = tep_get_event(pevent, idx); idx++)
> if (event == next_event)
> return tep_get_event(pevent, ++idx);
>
> Also, I think setting the idx to 1 in the loop is wrong. Why? think of
> this:
>
> first_event = trace_find_next_event(pevent, NULL);
>
> next_event = trace_find_next_event(pevent, first_event);
> for (i = 0; i < 5; i++)
> next_event = trace_find_next_event(pevent, next_event);
>
> second_event = trace_find_next_event(pevent, first_event);
>
> second_event would become NULL.

How about my proposal to instead change the loops in
trace-event-{python,perl}.c, the only callers of trace_find_next_event,
to be something akin to

[idx_type_for_tep_get_event] event_count = tep_get_events_count(pevent);
for ([idx_type_for_tep_get_event] idx = 0; idx < event_count; idx++)
{
struct tep_event *event = tep_get_events(...);

}

and just removing trace_find_next_event()? It's not a nice API imo, and
seems unnecessary given that the events aren't a linked list anymore.


> Care to send a formal patch?

Will do.

Greetings,

Andres Freund

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