1/*
2 * Copyright (C) 2015 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
17package android.net.netlink;
18
19import android.system.Os;
20import android.system.OsConstants;
21
22import java.nio.ByteBuffer;
23
24
25/**
26 * struct nda_cacheinfo
27 *
28 * see: <linux_src>/include/uapi/linux/neighbour.h
29 *
30 * @hide
31 */
32public class StructNdaCacheInfo {
33    // Already aligned.
34    public static final int STRUCT_SIZE = 16;
35
36    private static boolean hasAvailableSpace(ByteBuffer byteBuffer) {
37        return byteBuffer != null && byteBuffer.remaining() >= STRUCT_SIZE;
38    }
39
40    public static StructNdaCacheInfo parse(ByteBuffer byteBuffer) {
41        if (!hasAvailableSpace(byteBuffer)) { return null; }
42
43        // The ByteOrder must have already been set by the caller.  In most
44        // cases ByteOrder.nativeOrder() is correct, with the possible
45        // exception of usage within unittests.
46        final StructNdaCacheInfo struct = new StructNdaCacheInfo();
47        struct.ndm_used = byteBuffer.getInt();
48        struct.ndm_confirmed = byteBuffer.getInt();
49        struct.ndm_updated = byteBuffer.getInt();
50        struct.ndm_refcnt = byteBuffer.getInt();
51        return struct;
52    }
53
54    // TODO: investigate whether this can change during device runtime and
55    // decide what (if anything) should be done about that.
56    private static final long CLOCK_TICKS_PER_SECOND = Os.sysconf(OsConstants._SC_CLK_TCK);
57
58    private static long ticksToMilliSeconds(int intClockTicks) {
59        final long longClockTicks = (long) intClockTicks & 0xffffffff;
60        return (longClockTicks * 1000) / CLOCK_TICKS_PER_SECOND;
61    }
62
63    /**
64     * Explanatory notes, for reference.
65     *
66     * Before being returned to user space, the neighbor entry times are
67     * converted to clock_t's like so:
68     *
69     *     ndm_used      = jiffies_to_clock_t(now - neigh->used);
70     *     ndm_confirmed = jiffies_to_clock_t(now - neigh->confirmed);
71     *     ndm_updated   = jiffies_to_clock_t(now - neigh->updated);
72     *
73     * meaning that these values are expressed as "clock ticks ago".  To
74     * convert these clock ticks to seconds divide by sysconf(_SC_CLK_TCK).
75     * When _SC_CLK_TCK is 100, for example, the ndm_* times are expressed
76     * in centiseconds.
77     *
78     * These values are unsigned, but fortunately being expressed as "some
79     * clock ticks ago", these values are typically very small (and
80     * 2^31 centiseconds = 248 days).
81     *
82     * By observation, it appears that:
83     *     ndm_used: the last time ARP/ND took place for this neighbor
84     *     ndm_confirmed: the last time ARP/ND succeeded for this neighbor OR
85     *                    higher layer confirmation (TCP or MSG_CONFIRM)
86     *                    was received
87     *     ndm_updated: the time when the current NUD state was entered
88     */
89    public int ndm_used;
90    public int ndm_confirmed;
91    public int ndm_updated;
92    public int ndm_refcnt;
93
94    public StructNdaCacheInfo() {}
95
96    public long lastUsed() {
97        return ticksToMilliSeconds(ndm_used);
98    }
99
100    public long lastConfirmed() {
101        return ticksToMilliSeconds(ndm_confirmed);
102    }
103
104    public long lastUpdated() {
105        return ticksToMilliSeconds(ndm_updated);
106    }
107
108    @Override
109    public String toString() {
110        return "NdaCacheInfo{ "
111                + "ndm_used{" + lastUsed() + "}, "
112                + "ndm_confirmed{" + lastConfirmed() + "}, "
113                + "ndm_updated{" + lastUpdated() + "}, "
114                + "ndm_refcnt{" + ndm_refcnt + "} "
115                + "}";
116    }
117}
118