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/*
* Copyright (C) 2015 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.
*/
package com.android.net.module.util.netlink;
import static com.android.net.module.util.netlink.NetlinkUtils.ticksToMilliSeconds;
import java.nio.ByteBuffer;
/**
* struct nda_cacheinfo
*
* see: <linux_src>/include/uapi/linux/neighbour.h
*
* @hide
*/
public class StructNdaCacheInfo {
// Already aligned.
public static final int STRUCT_SIZE = 16;
private static boolean hasAvailableSpace(ByteBuffer byteBuffer) {
return byteBuffer != null && byteBuffer.remaining() >= STRUCT_SIZE;
}
/**
* Parse a nd cacheinfo netlink attribute from a {@link ByteBuffer}.
*
* @param byteBuffer The buffer from which to parse the nd cacheinfo attribute.
* @return the parsed nd cacheinfo attribute, or {@code null} if the nd cacheinfo attribute
* could not be parsed successfully (for example, if it was truncated).
*/
public static StructNdaCacheInfo parse(ByteBuffer byteBuffer) {
if (!hasAvailableSpace(byteBuffer)) return null;
// The ByteOrder must have already been set by the caller. In most
// cases ByteOrder.nativeOrder() is correct, with the possible
// exception of usage within unittests.
final StructNdaCacheInfo struct = new StructNdaCacheInfo();
struct.ndm_used = byteBuffer.getInt();
struct.ndm_confirmed = byteBuffer.getInt();
struct.ndm_updated = byteBuffer.getInt();
struct.ndm_refcnt = byteBuffer.getInt();
return struct;
}
/**
* Explanatory notes, for reference.
*
* Before being returned to user space, the neighbor entry times are
* converted to clock_t's like so:
*
* ndm_used = jiffies_to_clock_t(now - neigh->used);
* ndm_confirmed = jiffies_to_clock_t(now - neigh->confirmed);
* ndm_updated = jiffies_to_clock_t(now - neigh->updated);
*
* meaning that these values are expressed as "clock ticks ago". To
* convert these clock ticks to seconds divide by sysconf(_SC_CLK_TCK).
* When _SC_CLK_TCK is 100, for example, the ndm_* times are expressed
* in centiseconds.
*
* These values are unsigned, but fortunately being expressed as "some
* clock ticks ago", these values are typically very small (and
* 2^31 centiseconds = 248 days).
*
* By observation, it appears that:
* ndm_used: the last time ARP/ND took place for this neighbor
* ndm_confirmed: the last time ARP/ND succeeded for this neighbor OR
* higher layer confirmation (TCP or MSG_CONFIRM)
* was received
* ndm_updated: the time when the current NUD state was entered
*/
public int ndm_used;
public int ndm_confirmed;
public int ndm_updated;
public int ndm_refcnt;
public StructNdaCacheInfo() {}
/**
* The last time ARP/ND took place for this neighbor.
*/
public long lastUsed() {
return ticksToMilliSeconds(ndm_used);
}
/**
* The last time ARP/ND succeeded for this neighbor or higher layer confirmation (TCP or
* MSG_CONFIRM) was received.
*/
public long lastConfirmed() {
return ticksToMilliSeconds(ndm_confirmed);
}
/**
* The time when the current NUD state was entered.
*/
public long lastUpdated() {
return ticksToMilliSeconds(ndm_updated);
}
@Override
public String toString() {
return "NdaCacheInfo{ "
+ "ndm_used{" + lastUsed() + "}, "
+ "ndm_confirmed{" + lastConfirmed() + "}, "
+ "ndm_updated{" + lastUpdated() + "}, "
+ "ndm_refcnt{" + ndm_refcnt + "} "
+ "}";
}
}
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