linux-kernel - Re: [PATCH 3/3] tools lib traceevent: Introduce pevent

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Message-ID: <1339524114.13377.140.camel@gandalf.stny.rr.com>
Date:	Tue, 12 Jun 2012 14:01:54 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung.kim@....com>
Subject: Re: [PATCH 3/3] tools lib traceevent: Introduce pevent_strerror

On Tue, 2012-06-12 at 16:42 +0900, Namhyung Kim wrote:
> From: Namhyung Kim <namhyung.kim@....com>
> 
> The pevent_strerror() sets @buf to a string that describes the
> (libtraceevent-specific) error condition that is passed via @errnum.
> 
> This is similar to strerror_r() and does same thing if @errnum has a
> standard errno value.
> 
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/lib/traceevent/event-parse.c |   48 ++++++++++++++++++++++++++++++++++++
>  tools/lib/traceevent/event-parse.h |    2 ++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
> index 866bdca4825d..3ed2d9362e69 100644
> --- a/tools/lib/traceevent/event-parse.c
> +++ b/tools/lib/traceevent/event-parse.c
> @@ -4706,6 +4706,54 @@ enum pevent_errno pevent_parse_event(struct pevent *pevent, const char *buf,
>  	return ret;
>  }
>  
> +/*
> + * This must have a same ordering as the enum pevent_errno.
> + */
> +static const char * const pevent_error_str[] = {
> +	"failed to allocate memory",
> +	"failed to parse event",
> +	"failed to read event id",
> +	"failed to read event format",
> +	"failed to read event print fmt",
> +	"failed to allocate field name for ftrace",
> +};
> +
> +int pevent_strerror(struct pevent *pevent, enum pevent_errno errnum,
> +		    char *buf, size_t buflen)

Hmm, actually I wonder if we should put the error into the pevent
structure. Then we wouldn't even need to waste time to pass the data
through.

That is, you can simply do:

	ret = pevent_foo();
	if (ret < 0) {
		pevent_strerr(pevent, buf, buflen);
		printf("%s\n", buf);
	}

Perhaps even include a pevent_perror(), to just do:

	if (ret < 0) {
		pevent_perror(pevent);
		return ret;
	}

-- Steve

> +{
> +	int idx;
> +	const char *msg;
> +
> +	if (errnum >= 0) {
> +		strerror_r(errnum, buf, buflen);
> +		return 0;
> +	}
> +
> +	if (errnum <  __PEVENT_ERRNO__START ||
> +	    errnum >= __PEVENT_ERRNO__END)
> +		return -1;
> +
> +	idx = errnum - __PEVENT_ERRNO__START;
> +	msg = pevent_error_str[idx];
> +
> +	switch (errnum) {
> +	case PEVENT_ERRNO__MEM_ALLOC_FAILED:
> +	case PEVENT_ERRNO__PARSE_EVENT_FAILED:
> +	case PEVENT_ERRNO__READ_ID_FAILED:
> +	case PEVENT_ERRNO__READ_FORMAT_FAILED:
> +	case PEVENT_ERRNO__READ_PRINT_FAILED:
> +	case PEVENT_ERRNO__OLD_FTRACE_ARG_FAILED:
> +		snprintf(buf, buflen, "%s", msg);
> +		break;
> +
> +	default:
> +		/* cannot reach here */
> +		break;
> +	}
> +
> +	return 0;
> +}
> +
>  int get_field_val(struct trace_seq *s, struct format_field *field,
>  		  const char *name, struct pevent_record *record,
>  		  unsigned long long *val, int err)
> diff --git a/tools/lib/traceevent/event-parse.h b/tools/lib/traceevent/event-parse.h
> index 24b7649d530b..7e90aba20850 100644
> --- a/tools/lib/traceevent/event-parse.h
> +++ b/tools/lib/traceevent/event-parse.h
> @@ -576,6 +576,8 @@ int pevent_data_pid(struct pevent *pevent, struct pevent_record *rec);
>  const char *pevent_data_comm_from_pid(struct pevent *pevent, int pid);
>  void pevent_event_info(struct trace_seq *s, struct event_format *event,
>  		       struct pevent_record *record);
> +int pevent_strerror(struct pevent *pevent, enum pevent_errno errnum,
> +		    char *buf, size_t buflen);
>  
>  struct event_format **pevent_list_events(struct pevent *pevent, enum event_sort_type);
>  struct format_field **pevent_event_common_fields(struct event_format *event);


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