NetworkStats - no need for xt_qtaguid clat bw fixups am: d1dd2f9c am: df27973f

    }

    /**

     * Calculate and apply adjustments to captured statistics for 464xlat traffic counted twice.

     * Calculate and apply adjustments to captured statistics for 464xlat traffic.

     *

     * <p>This mutates stacked traffic stats, to account for IPv4/IPv6 header size difference.

     *

     * <p>This mutates both base and stacked traffic stats, to account respectively for

     * double-counted traffic and IPv4/IPv6 header size difference.

     * <p>UID stats, which are only accounted on the stacked interface, need to be increased

     * by 20 bytes/packet to account for translation overhead.

     *

     * <p>For 464xlat traffic, xt_qtaguid sees every IPv4 packet twice, once as a native IPv4

     * packet on the stacked interface, and once as translated to an IPv6 packet on the

     * base interface. For correct stats accounting on the base interface, if using xt_qtaguid,

     * every rx 464xlat packet needs to be subtracted from the root UID on the base interface

     * (http://b/12249687, http:/b/33681750), and every tx 464xlat packet which was counted onto

     * clat uid should be ignored.

     * <p>The potential additional overhead of 8 bytes/packet for ip fragments is ignored.

     *

     * As for eBPF, the per uid stats is collected by different hook, the rx packets on base

     * interface will not be counted. Thus, the adjustment on root uid is not needed. However, the

     * tx traffic counted in the same way xt_qtaguid does, so the traffic on clat uid still

     * needs to be ignored.

     * <p>Interface stats need to sum traffic on both stacked and base interface because:

     *   - eBPF offloaded packets appear only on the stacked interface

     *   - Non-offloaded ingress packets appear only on the stacked interface

     *     (due to iptables raw PREROUTING drop rules)

     *   - Non-offloaded egress packets appear only on the stacked interface

     *     (due to ignoring traffic from clat daemon by uid match)

     * (and of course the 20 bytes/packet overhead needs to be applied to stacked interface stats)

     *

     * <p>This method will behave fine if {@code stackedIfaces} is an non-synchronized but add-only

     * {@code ConcurrentHashMap}

     */

    public static void apply464xlatAdjustments(NetworkStats baseTraffic,

            NetworkStats stackedTraffic, Map<String, String> stackedIfaces, boolean useBpfStats) {

        // Total 464xlat traffic to subtract from uid 0 on all base interfaces.

        // stackedIfaces may grow afterwards, but NetworkStats will just be resized automatically.

        final NetworkStats adjustments = new NetworkStats(0, stackedIfaces.size());

        // For recycling

        Entry entry = null;

        Entry adjust = new NetworkStats.Entry(IFACE_ALL, 0, 0, 0, 0, 0, 0, 0L, 0L, 0L, 0L, 0L);

        for (int i = 0; i < stackedTraffic.size; i++) {

            entry = stackedTraffic.getValues(i, entry);

            if (entry.iface == null || !entry.iface.startsWith(CLATD_INTERFACE_PREFIX)) {

                continue;

            }

            final String baseIface = stackedIfaces.get(entry.iface);

            if (baseIface == null) {

                continue;

            }

            // Subtract xt_qtaguid 464lat rx traffic seen for the root UID on the current base

            // interface. As for eBPF, the per uid stats is collected by different hook, the rx

            // packets on base interface will not be counted.

            adjust.iface = baseIface;

            if (!useBpfStats) {

                adjust.rxBytes = -(entry.rxBytes + entry.rxPackets * IPV4V6_HEADER_DELTA);

                adjust.rxPackets = -entry.rxPackets;

            }

            adjustments.combineValues(adjust);

            if (entry == null) continue;

            if (entry.iface == null) continue;

            if (!entry.iface.startsWith(CLATD_INTERFACE_PREFIX)) continue;

            // For 464xlat traffic, per uid stats only counts the bytes of the native IPv4 packet

            // sent on the stacked interface with prefix "v4-" and drops the IPv6 header size after

            // unwrapping. To account correctly for on-the-wire traffic, add the 20 additional bytes

            // difference for all packets (http://b/12249687, http:/b/33681750).

            //

            // Note: this doesn't account for LRO/GRO/GSO/TSO (ie. >mtu) traffic correctly, nor

            // does it correctly account for the 8 extra bytes in the IPv6 fragmentation header.

            //

            // While the ebpf code path does try to simulate proper post segmentation packet

            // counts, we have nothing of the sort of xt_qtaguid stats.

            entry.rxBytes += entry.rxPackets * IPV4V6_HEADER_DELTA;

            entry.txBytes += entry.txPackets * IPV4V6_HEADER_DELTA;

            stackedTraffic.setValues(i, entry);

        }

        // Traffic on clat uid is v6 tx traffic that is already counted with app uid on the stacked

        // v4 interface, so it needs to be removed to avoid double-counting.

        // Theoretically there should be no traffic accounted to the clat daemon's uid:

        //   see ebpf program 'netd.c's early returns

        //   and iptables '-m owner --uid-owner clat -j RETURN' rules prior to accounting

        // TODO: remove this - should definitely be safe once ebpf only.

        baseTraffic.removeUids(new int[] {CLAT_UID});

        baseTraffic.combineAllValues(adjustments);

    }

    /**