resolv_stats.h revision 4d8e740b0868b2670599b949ff07d74e5f317114 
1/*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef _RES_STATS_H
18#define _RES_STATS_H
19
20#include <stdbool.h>
21#include <stdint.h>
22#include <time.h>
23
24#include "resolv_params.h"
25
26#define RCODE_INTERNAL_ERROR    254
27#define RCODE_TIMEOUT           255
28
29/*
30 * Resolver reachability statistics and run-time parameters.
31 */
32
33struct __res_sample {
34    time_t			at;    // time in s at which the sample was recorded
35    uint16_t			rtt;   // round-trip time in ms
36    uint8_t			rcode; // the DNS rcode or RCODE_XXX defined above
37};
38
39struct __res_stats {
40    // Stats of the last <sample_count> queries.
41    struct __res_sample		samples[MAXNSSAMPLES];
42    // The number of samples stored.
43    uint8_t			sample_count;
44    // The next sample to modify.
45    uint8_t			sample_next;
46};
47
48/* Calculate the round-trip-time from start time t0 and end time t1. */
49int
50_res_stats_calculate_rtt(const struct timespec* t1, const struct timespec* t0);
51
52/* Initialize a sample for calculating server reachability statistics. */
53extern void
54_res_stats_set_sample(struct __res_sample* sample, time_t now, int rcode, int rtt);
55
56/* Aggregates the reachability statistics for the given server based on on the stored samples. */
57extern void
58_res_stats_aggregate(struct __res_stats* stats, int* successes, int* errors, int* timeouts,
59             int* internal_errors, int* rtt_avg, time_t* last_sample_time);
60
61/* Returns true if the server is considered unusable, i.e. if the success rate is not lower than the
62 * threshold for the stored stored samples. If not enough samples are stored, the server is
63 * considered usable.
64 */
65extern bool
66_res_stats_usable_server(const struct __res_params* params, struct __res_stats* stats);
67
68/* Returns an array of bools indicating which servers are considered good */
69extern void
70_res_stats_get_usable_servers(const struct __res_params* params, struct __res_stats stats[MAXNS],
71        int nscount, bool valid_servers[MAXNS]);
72
73#endif  // _RES_STATS_H
74