content: /*
   * 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 android.net.netlink;
  
  import android.system.Os;
  import android.system.OsConstants;
  
  import java.nio.ByteBuffer;
  
  
  /**
   * struct nda_cacheinfo
   *
   * see: &lt;linux_src&gt;/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;
      }
  
      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;
      }
  
      // TODO: investigate whether this can change during device runtime and
      // decide what (if anything) should be done about that.
      private static final long CLOCK_TICKS_PER_SECOND = Os.sysconf(OsConstants._SC_CLK_TCK);
  
      private static long ticksToMilliSeconds(int intClockTicks) {
          final long longClockTicks = (long) intClockTicks & 0xffffffff;
          return (longClockTicks * 1000) / CLOCK_TICKS_PER_SECOND;
      }
  
      /**
       * 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() {}
  
      public long lastUsed() {
          return ticksToMilliSeconds(ndm_used);
      }
  
      public long lastConfirmed() {
          return ticksToMilliSeconds(ndm_confirmed);
      }
  
      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 + "} "
                  + "}";
      }
  }
  