tools lib traceevent: Introduce pevent_strerror

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.

To sync error string with its code, define PEVENT_ERRORS with _PE()
macro and use it as suggested by Steven.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1345618831-9148-4-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/traceevent/event-parse.c

@@ -4795,6 +4795,49 @@ enum pevent_errno pevent_parse_event(struct pevent *pevent, const char *buf,
 	return ret;
 }
 
+#undef _PE
+#define _PE(code, str) str
+static const char * const pevent_error_str[] = {
+	PEVENT_ERRORS
+};
+#undef _PE
+
+int pevent_strerror(struct pevent *pevent, enum pevent_errno errnum,
+		    char *buf, size_t buflen)
+{
+	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)

tools/lib/traceevent/event-parse.h

@@ -345,6 +345,16 @@ enum pevent_flag {
 	PEVENT_NSEC_OUTPUT		= 1,	/* output in NSECS */
 };
 
+#define PEVENT_ERRORS 							      \
+	_PE(MEM_ALLOC_FAILED,	"failed to allocate memory"),		      \
+	_PE(PARSE_EVENT_FAILED,	"failed to parse event"),		      \
+	_PE(READ_ID_FAILED,	"failed to read event id"),		      \
+	_PE(READ_FORMAT_FAILED,	"failed to read event format"),		      \
+	_PE(READ_PRINT_FAILED,	"failed to read event print fmt"), 	      \
+	_PE(OLD_FTRACE_ARG_FAILED,"failed to allocate field name for ftrace")
+
+#undef _PE
+#define _PE(__code, __str) PEVENT_ERRNO__ ## __code
 enum pevent_errno {
 	PEVENT_ERRNO__SUCCESS			= 0,
 
@@ -357,15 +367,11 @@ enum pevent_errno {
 	 */
 	__PEVENT_ERRNO__START			= -100000,
 
-	PEVENT_ERRNO__MEM_ALLOC_FAILED		= __PEVENT_ERRNO__START,
-	PEVENT_ERRNO__PARSE_EVENT_FAILED,
-	PEVENT_ERRNO__READ_ID_FAILED,
-	PEVENT_ERRNO__READ_FORMAT_FAILED,
-	PEVENT_ERRNO__READ_PRINT_FAILED,
-	PEVENT_ERRNO__OLD_FTRACE_ARG_FAILED,
+	PEVENT_ERRORS,
 
 	__PEVENT_ERRNO__END,
 };
+#undef _PE
 
 struct cmdline;
 struct cmdline_list;
@@ -583,6 +589,8 @@ 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);