On Tue, Jun 02, 2015 at 10:12:02AM -0700, Sukadev Bhattiprolu wrote:

SNIP

+ * If we fail to locate/process JSON and map files, create a NULL mapping
+ * table. This would at least allow perf to build even if we can't find/use
+ * the aliases.
+ */
+static void create_empty_mapping(const char *output_file)
+{
+	FILE *outfp;
+
+	pr_info("%s: Creating empty pmu_events_map[] table\n", prog);
+
+	/* Unlink file to clear any partial writes to it */
+	unlink(output_file);
+
+	outfp = fopen(output_file, "a");

you could open with "w+" and save the unlink call

SNIP

+int main(int argc, char *argv[])
+{
+	int rc;
+	int flags;
+	int maxfds;
+	char dirname[PATH_MAX];
+
+	const char *arch;
+	const char *output_file;
+	const char *start_dirname;
+
+	prog = basename(argv[0]);
+	if (argc < 4) {
+		pr_err("Usage: %s <arch> <starting_dir> <output_file>\n", prog);
+		return 1;
+	}
+
+	arch = argv[1];
+	start_dirname = argv[2];
+	output_file = argv[3];
+
+	if (argc > 4)
+		verbose = atoi(argv[4]);
+
+	unlink(output_file);
+	eventsfp = fopen(output_file, "a");

ditto

SNIP