linux-kernel - Re: [RFC PATCH] tools lib traceevent: Allow setting an alternative symbol resolver

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Date:	Thu, 23 Jul 2015 17:35:24 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	David Ahern <dsahern@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Borislav Petkov <bp@...e.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] tools lib traceevent: Allow setting an alternative
 symbol resolver

On Thu, 23 Jul 2015 18:25:36 -0300
Arnaldo Carvalho de Melo <acme@...nel.org> wrote:

> Like this?

Yep, but some comments.

> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
> index cc25f059ab3d..7f9266225f11 100644
> --- a/tools/lib/traceevent/event-parse.c
> +++ b/tools/lib/traceevent/event-parse.c
> @@ -418,7 +418,7 @@ static int func_map_init(struct pevent *pevent)
>  }
>  
>  static struct func_map *
> -find_func(struct pevent *pevent, unsigned long long addr)
> +__find_func(struct pevent *pevent, unsigned long long addr)
>  {
>  	struct func_map *func;
>  	struct func_map key;
> @@ -434,6 +434,60 @@ find_func(struct pevent *pevent, unsigned long long addr)
>  	return func;
>  }
>  
> +struct func_resolver {
> +	pevent_func_resolver_t *func;
> +	void		       *priv;
> +	struct func_map	       map;
> +};
> +
> +/**
> + * pevent_set_function_resolver - set an alternative function resolver
> + * @pevent: handle for the pevent
> + * @resolver: function to be used
> + * @priv: resolver function private state.
> + *
> + * Some tools may have already a way to resolve kernel functions, allow them to
> + * keep using it instead of duplicating all the entries inside
> + * pevent->funclist.
> + */
> +int pevent_set_function_resolver(struct pevent *pevent,
> +				 pevent_func_resolver_t *func, void *priv)
> +{
> +	struct func_resolver *resolver = malloc(sizeof(*resolver));
> +
> +	if (resolver == NULL) {
> +		errno = ENOMEM;

Why set errno, wont a failed malloc set it for us?

> +		return -1;
> +	}
> +
> +	resolver->func = func;
> +	resolver->priv = priv;
> +
> +	free(pevent->func_resolver);
> +	pevent->func_resolver = resolver;

Also I wonder if we should add a way to clear the resolver. That is,
you want to use the default resolver?

Not really a necessity, as I don't see any current programs using it,
but it would complete the interface.

-- Steve

> +
> +	return 0;
> +}
> +
> +static struct func_map *
> +find_func(struct pevent *pevent, unsigned long long addr)
> +{
> +	struct func_map *map;
> +
> +	if (!pevent->func_resolver)
> +		return __find_func(pevent, addr);
> +
> +	map = &pevent->func_resolver->map;
> +	map->mod  = NULL;
> +	map->addr = addr;
> +	map->func = pevent->func_resolver->func(pevent->func_resolver->priv,
> +						&map->addr, &map->mod);
> +	if (map->func == NULL)
> +		return NULL;
> +
> +	return map;
> +}
> +
>  /**
>   * pevent_find_function - find a function by a given address
>   * @pevent: handle for the pevent
> @@ -6564,6 +6618,7 @@ void pevent_free(struct pevent *pevent)
>  	free(pevent->trace_clock);
>  	free(pevent->events);
>  	free(pevent->sort_events);
> +	free(pevent->func_resolver);
>  
>  	free(pevent);
>  }
> diff --git a/tools/lib/traceevent/event-parse.h b/tools/lib/traceevent/event-parse.h
> index 063b1971eb35..416e1bd9fe33 100644
> --- a/tools/lib/traceevent/event-parse.h
> +++ b/tools/lib/traceevent/event-parse.h
> @@ -453,6 +453,10 @@ struct cmdline_list;
>  struct func_map;
>  struct func_list;
>  struct event_handler;
> +struct func_resolver;
> +
> +typedef char *(pevent_func_resolver_t)(void *priv,
> +				       unsigned long long *addrp, char **modp);
>  
>  struct pevent {
>  	int ref_count;
> @@ -481,6 +485,7 @@ struct pevent {
>  	int cmdline_count;
>  
>  	struct func_map *func_map;
> +	struct func_resolver *func_resolver;
>  	struct func_list *funclist;
>  	unsigned int func_count;
>  
> @@ -611,6 +616,8 @@ enum trace_flag_type {
>  	TRACE_FLAG_SOFTIRQ		= 0x10,
>  };
>  
> +int pevent_set_function_resolver(struct pevent *pevent,
> +				 pevent_func_resolver_t *func, void *priv);
>  int pevent_register_comm(struct pevent *pevent, const char *comm, int pid);
>  int pevent_register_trace_clock(struct pevent *pevent, const char *trace_clock);
>  int pevent_register_function(struct pevent *pevent, char *name,

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