perf record: Improve write_output error message

Improve the error message from write_output() to say what failed to
write and give the error number.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1382099356-4918-4-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -88,7 +88,7 @@ static int write_output(struct perf_record *rec, void *buf, size_t size)
 		int ret = write(rec->output, buf, size);
 
 		if (ret < 0) {
-			pr_err("failed to write\n");
+			pr_err("failed to write perf data, error: %m\n");
 			return -1;
 		}