return -1;
 }
 
-static int
-perf_pmu__parse_per_pkg(struct perf_pmu *pmu, struct perf_pmu_alias *alias)
+static bool perf_pmu__parse_event_source_bool(const char *pmu_name, const char *event_name,
+                                             const char *suffix)
 {
        char path[PATH_MAX];
        size_t len;
 
        len = perf_pmu__event_source_devices_scnprintf(path, sizeof(path));
        if (!len)
-               return 0;
-       scnprintf(path + len, sizeof(path) - len, "%s/events/%s.per-pkg", pmu->name, alias->name);
+               return false;
+
+       scnprintf(path + len, sizeof(path) - len, "%s/events/%s.%s", pmu_name, event_name, suffix);
 
        fd = open(path, O_RDONLY);
        if (fd == -1)
-               return -1;
+               return false;
 
-       close(fd);
+#ifndef NDEBUG
+       {
+               char buf[8];
 
-       alias->per_pkg = true;
-       return 0;
+               len = read(fd, buf, sizeof(buf));
+               assert(len == 1 || len == 2);
+               assert(buf[0] == '1');
+       }
+#endif
+
+       close(fd);
+       return true;
 }
 
-static int perf_pmu__parse_snapshot(struct perf_pmu *pmu, struct perf_pmu_alias *alias)
+static void perf_pmu__parse_per_pkg(struct perf_pmu *pmu, struct perf_pmu_alias *alias)
 {
-       char path[PATH_MAX];
-       size_t len;
-       int fd;
-
-       len = perf_pmu__event_source_devices_scnprintf(path, sizeof(path));
-       if (!len)
-               return 0;
-       scnprintf(path + len, sizeof(path) - len, "%s/events/%s.snapshot", pmu->name, alias->name);
-
-       fd = open(path, O_RDONLY);
-       if (fd == -1)
-               return -1;
+       alias->per_pkg = perf_pmu__parse_event_source_bool(pmu->name, alias->name, "per-pkg");
+}
 
-       alias->snapshot = true;
-       close(fd);
-       return 0;
+static void perf_pmu__parse_snapshot(struct perf_pmu *pmu, struct perf_pmu_alias *alias)
+{
+       alias->snapshot = perf_pmu__parse_event_source_bool(pmu->name, alias->name, "snapshot");
 }
 
 /* Delete an alias entry. */