Ignore unreliable DNS servers.
Collect statistics about DNS query success state and delay. Ignore
servers that have been tried at least five times and have a success rate
of < 0.25. Retry these servers once every 180s.
Bug: 25731675
Change-Id: I78e24f43e388dca82fb81835e1796f4c7dce8da3
diff --git a/libc/dns/include/resolv_params.h b/libc/dns/include/resolv_params.h
new file mode 100644
index 0000000..353ae4d
--- /dev/null
+++ b/libc/dns/include/resolv_params.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _RESOLV_PARAMS_H
+#define _RESOLV_PARAMS_H
+
+#include <stdint.h>
+
+/* Hard-coded defines */
+#define MAXNS 3 /* max # name servers we'll track */
+#define MAXNSSAMPLES 64 /* max # samples to store per server */
+
+/* Defaults used for initializing __res_params */
+#define SUCCESS_THRESHOLD 75 /* if successes * 100 / total_samples is less than
+ * this value, the server is considered failing
+ */
+#define NSSAMPLE_VALIDITY 1800 /* Sample validity in seconds.
+ * Set to -1 to disable skipping failing
+ * servers.
+ */
+
+/* per-netid configuration parameters passed from netd to the resolver */
+struct __res_params {
+ uint16_t sample_validity; // sample lifetime in s
+ // threshold of success / total samples below which a server is considered broken
+ uint8_t success_threshold; // 0: disable, value / 100 otherwise
+ uint8_t min_samples; // min # samples needed for statistics to be considered meaningful
+ uint8_t max_samples; // max # samples taken into account for statistics
+} __attribute__((__packed__));
+
+#endif // _RESOLV_PARAMS_H