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 ===============================================
 Ethernet switch device driver model (switchdev)
 ===============================================
 
 Copyright |copy| 2014 Jiri Pirko <jiri@resnulli.us>
 
 Copyright |copy| 2014-2015 Scott Feldman <sfeldma@gmail.com>
 
 
 The Ethernet switch device driver model (switchdev) is an in-kernel driver
 model for switch devices which offload the forwarding (data) plane from the
 kernel.
 
 Figure 1 is a block diagram showing the components of the switchdev model for
 an example setup using a data-center-class switch ASIC chip.  Other setups
 with SR-IOV or soft switches, such as OVS, are possible.
 
 ::
 
 
                              User-space tools
 
        user space                   |
       +-------------------------------------------------------------------+
        kernel                       | Netlink
                                     |
                      +--------------+-------------------------------+
                      |         Network stack                        |
                      |           (Linux)                            |
                      |                                              |
                      +----------------------------------------------+
 
                            sw1p2     sw1p4     sw1p6
                       sw1p1  +  sw1p3  +  sw1p5  +          eth1
                         +    |    +    |    +    |            +
                         |    |    |    |    |    |            |
                      +--+----+----+----+----+----+---+  +-----+-----+
                      |         Switch driver         |  |    mgmt   |
                      |        (this document)        |  |   driver  |
                      |                               |  |           |
                      +--------------+----------------+  +-----------+
                                     |
        kernel                       | HW bus (eg PCI)
       +-------------------------------------------------------------------+
        hardware                     |
                      +--------------+----------------+
                      |         Switch device (sw1)   |
                      |  +----+                       +--------+
                      |  |    v offloaded data path   | mgmt port
                      |  |    |                       |
                      +--|----|----+----+----+----+---+
                         |    |    |    |    |    |
                         +    +    +    +    +    +
                        p1   p2   p3   p4   p5   p6
 
                              front-panel ports
 
 
                                     Fig 1.
 
 
 Include Files
 -------------
 
 ::
 
     #include <linux/netdevice.h>
     #include <net/switchdev.h>
 
 
 Configuration
 -------------
 
 Use "depends NET_SWITCHDEV" in driver's Kconfig to ensure switchdev model
 support is built for driver.
 
 
 Switch Ports
 ------------
 
 On switchdev driver initialization, the driver will allocate and register a
 struct net_device (using register_netdev()) for each enumerated physical switch
 port, called the port netdev.  A port netdev is the software representation of
 the physical port and provides a conduit for control traffic to/from the
 controller (the kernel) and the network, as well as an anchor point for higher
 level constructs such as bridges, bonds, VLANs, tunnels, and L3 routers.  Using
 standard netdev tools (iproute2, ethtool, etc), the port netdev can also
 provide to the user access to the physical properties of the switch port such
 as PHY link state and I/O statistics.
 
 There is (currently) no higher-level kernel object for the switch beyond the
 port netdevs.  All of the switchdev driver ops are netdev ops or switchdev ops.
 
 A switch management port is outside the scope of the switchdev driver model.
 Typically, the management port is not participating in offloaded data plane and
 is loaded with a different driver, such as a NIC driver, on the management port
 device.
 
 Switch ID
 ^^^^^^^^^
 
 The switchdev driver must implement the net_device operation
 ndo_get_port_parent_id for each port netdev, returning the same physical ID for
 each port of a switch. The ID must be unique between switches on the same
 system. The ID does not need to be unique between switches on different
 systems.
 
 The switch ID is used to locate ports on a switch and to know if aggregated
 ports belong to the same switch.
 
 Port Netdev Naming
 ^^^^^^^^^^^^^^^^^^
 
 Udev rules should be used for port netdev naming, using some unique attribute
 of the port as a key, for example the port MAC address or the port PHYS name.
 Hard-coding of kernel netdev names within the driver is discouraged; let the
 kernel pick the default netdev name, and let udev set the final name based on a
 port attribute.
 
 Using port PHYS name (ndo_get_phys_port_name) for the key is particularly
 useful for dynamically-named ports where the device names its ports based on
 external configuration.  For example, if a physical 40G port is split logically
 into 4 10G ports, resulting in 4 port netdevs, the device can give a unique
 name for each port using port PHYS name.  The udev rule would be::
 
     SUBSYSTEM=="net", ACTION=="add", ATTR{phys_switch_id}=="<phys_switch_id>", \
             ATTR{phys_port_name}!="", NAME="swX$attr{phys_port_name}"
 
 Suggested naming convention is "swXpYsZ", where X is the switch name or ID, Y
 is the port name or ID, and Z is the sub-port name or ID.  For example, sw1p1s0
 would be sub-port 0 on port 1 on switch 1.
 
 Port Features
 ^^^^^^^^^^^^^
 
 NETIF_F_NETNS_LOCAL
 
 If the switchdev driver (and device) only supports offloading of the default
 network namespace (netns), the driver should set this feature flag to prevent
 the port netdev from being moved out of the default netns.  A netns-aware
 driver/device would not set this flag and be responsible for partitioning
 hardware to preserve netns containment.  This means hardware cannot forward
 traffic from a port in one namespace to another port in another namespace.
 
 Port Topology
 ^^^^^^^^^^^^^
 
 The port netdevs representing the physical switch ports can be organized into
 higher-level switching constructs.  The default construct is a standalone
 router port, used to offload L3 forwarding.  Two or more ports can be bonded
 together to form a LAG.  Two or more ports (or LAGs) can be bridged to bridge
 L2 networks.  VLANs can be applied to sub-divide L2 networks.  L2-over-L3
 tunnels can be built on ports.  These constructs are built using standard Linux
 tools such as the bridge driver, the bonding/team drivers, and netlink-based
 tools such as iproute2.
 
 The switchdev driver can know a particular port's position in the topology by
 monitoring NETDEV_CHANGEUPPER notifications.  For example, a port moved into a
 bond will see its upper master change.  If that bond is moved into a bridge,
 the bond's upper master will change.  And so on.  The driver will track such
 movements to know what position a port is in in the overall topology by
 registering for netdevice events and acting on NETDEV_CHANGEUPPER.
 
 L2 Forwarding Offload
 ---------------------
 
 The idea is to offload the L2 data forwarding (switching) path from the kernel
 to the switchdev device by mirroring bridge FDB entries down to the device.  An
 FDB entry is the {port, MAC, VLAN} tuple forwarding destination.
 
 To offloading L2 bridging, the switchdev driver/device should support:
 
         - Static FDB entries installed on a bridge port
         - Notification of learned/forgotten src mac/vlans from device
         - STP state changes on the port
         - VLAN flooding of multicast/broadcast and unknown unicast packets
 
 Static FDB Entries
 ^^^^^^^^^^^^^^^^^^
 
 A driver which implements the ``ndo_fdb_add``, ``ndo_fdb_del`` and
 ``ndo_fdb_dump`` operations is able to support the command below, which adds a
 static bridge FDB entry::
 
         bridge fdb add dev DEV ADDRESS [vlan VID] [self] static
 
 (the "static" keyword is non-optional: if not specified, the entry defaults to
 being "local", which means that it should not be forwarded)
 
 The "self" keyword (optional because it is implicit) has the role of
 instructing the kernel to fulfill the operation through the ``ndo_fdb_add``
 implementation of the ``DEV`` device itself. If ``DEV`` is a bridge port, this
 will bypass the bridge and therefore leave the software database out of sync
 with the hardware one.
 
 To avoid this, the "master" keyword can be used::
 
         bridge fdb add dev DEV ADDRESS [vlan VID] master static
 
 The above command instructs the kernel to search for a master interface of
 ``DEV`` and fulfill the operation through the ``ndo_fdb_add`` method of that.
 This time, the bridge generates a ``SWITCHDEV_FDB_ADD_TO_DEVICE`` notification
 which the port driver can handle and use it to program its hardware table. This
 way, the software and the hardware database will both contain this static FDB
 entry.
 
 Note: for new switchdev drivers that offload the Linux bridge, implementing the
 ``ndo_fdb_add`` and ``ndo_fdb_del`` bridge bypass methods is strongly
 discouraged: all static FDB entries should be added on a bridge port using the
 "master" flag. The ``ndo_fdb_dump`` is an exception and can be implemented to
 visualize the hardware tables, if the device does not have an interrupt for
 notifying the operating system of newly learned/forgotten dynamic FDB
 addresses. In that case, the hardware FDB might end up having entries that the
 software FDB does not, and implementing ``ndo_fdb_dump`` is the only way to see
 them.
 
 Note: by default, the bridge does not filter on VLAN and only bridges untagged
 traffic.  To enable VLAN support, turn on VLAN filtering::
 
         echo 1 >/sys/class/net/<bridge>/bridge/vlan_filtering
 
 Notification of Learned/Forgotten Source MAC/VLANs
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 The switch device will learn/forget source MAC address/VLAN on ingress packets
 and notify the switch driver of the mac/vlan/port tuples.  The switch driver,
 in turn, will notify the bridge driver using the switchdev notifier call::
 
         err = call_switchdev_notifiers(val, dev, info, extack);
 
 Where val is SWITCHDEV_FDB_ADD when learning and SWITCHDEV_FDB_DEL when
 forgetting, and info points to a struct switchdev_notifier_fdb_info.  On
 SWITCHDEV_FDB_ADD, the bridge driver will install the FDB entry into the
 bridge's FDB and mark the entry as NTF_EXT_LEARNED.  The iproute2 bridge
 command will label these entries "offload"::
 
         $ bridge fdb
         52:54:00:12:35:01 dev sw1p1 master br0 permanent
         00:02:00:00:02:00 dev sw1p1 master br0 offload
         00:02:00:00:02:00 dev sw1p1 self
         52:54:00:12:35:02 dev sw1p2 master br0 permanent
         00:02:00:00:03:00 dev sw1p2 master br0 offload
         00:02:00:00:03:00 dev sw1p2 self
         33:33:00:00:00:01 dev eth0 self permanent
         01:00:5e:00:00:01 dev eth0 self permanent
         33:33:ff:00:00:00 dev eth0 self permanent
         01:80:c2:00:00:0e dev eth0 self permanent
         33:33:00:00:00:01 dev br0 self permanent
         01:00:5e:00:00:01 dev br0 self permanent
         33:33:ff:12:35:01 dev br0 self permanent
 
 Learning on the port should be disabled on the bridge using the bridge command::
 
         bridge link set dev DEV learning off
 
 Learning on the device port should be enabled, as well as learning_sync::
 
         bridge link set dev DEV learning on self
         bridge link set dev DEV learning_sync on self
 
 Learning_sync attribute enables syncing of the learned/forgotten FDB entry to
 the bridge's FDB.  It's possible, but not optimal, to enable learning on the
 device port and on the bridge port, and disable learning_sync.
 
 To support learning, the driver implements switchdev op
 switchdev_port_attr_set for SWITCHDEV_ATTR_PORT_ID_{PRE}_BRIDGE_FLAGS.
 
 FDB Ageing
 ^^^^^^^^^^
 
 The bridge will skip ageing FDB entries marked with NTF_EXT_LEARNED and it is
 the responsibility of the port driver/device to age out these entries.  If the
 port device supports ageing, when the FDB entry expires, it will notify the
 driver which in turn will notify the bridge with SWITCHDEV_FDB_DEL.  If the
 device does not support ageing, the driver can simulate ageing using a
 garbage collection timer to monitor FDB entries.  Expired entries will be
 notified to the bridge using SWITCHDEV_FDB_DEL.  See rocker driver for
 example of driver running ageing timer.
 
 To keep an NTF_EXT_LEARNED entry "alive", the driver should refresh the FDB
 entry by calling call_switchdev_notifiers(SWITCHDEV_FDB_ADD, ...).  The
 notification will reset the FDB entry's last-used time to now.  The driver
 should rate limit refresh notifications, for example, no more than once a
 second.  (The last-used time is visible using the bridge -s fdb option).
 
 STP State Change on Port
 ^^^^^^^^^^^^^^^^^^^^^^^^
 
 Internally or with a third-party STP protocol implementation (e.g. mstpd), the
 bridge driver maintains the STP state for ports, and will notify the switch
 driver of STP state change on a port using the switchdev op
 switchdev_attr_port_set for SWITCHDEV_ATTR_PORT_ID_STP_UPDATE.
 
 State is one of BR_STATE_*.  The switch driver can use STP state updates to
 update ingress packet filter list for the port.  For example, if port is
 DISABLED, no packets should pass, but if port moves to BLOCKED, then STP BPDUs
 and other IEEE 01:80:c2:xx:xx:xx link-local multicast packets can pass.
 
 Note that STP BDPUs are untagged and STP state applies to all VLANs on the port
 so packet filters should be applied consistently across untagged and tagged
 VLANs on the port.
 
 Flooding L2 domain
 ^^^^^^^^^^^^^^^^^^
 
 For a given L2 VLAN domain, the switch device should flood multicast/broadcast
 and unknown unicast packets to all ports in domain, if allowed by port's
 current STP state.  The switch driver, knowing which ports are within which
 vlan L2 domain, can program the switch device for flooding.  The packet may
 be sent to the port netdev for processing by the bridge driver.  The
 bridge should not reflood the packet to the same ports the device flooded,
 otherwise there will be duplicate packets on the wire.
 
 To avoid duplicate packets, the switch driver should mark a packet as already
 forwarded by setting the skb->offload_fwd_mark bit. The bridge driver will mark
 the skb using the ingress bridge port's mark and prevent it from being forwarded
 through any bridge port with the same mark.
 
 It is possible for the switch device to not handle flooding and push the
 packets up to the bridge driver for flooding.  This is not ideal as the number
 of ports scale in the L2 domain as the device is much more efficient at
 flooding packets that software.
 
 If supported by the device, flood control can be offloaded to it, preventing
 certain netdevs from flooding unicast traffic for which there is no FDB entry.
 
 IGMP Snooping
 ^^^^^^^^^^^^^
 
 In order to support IGMP snooping, the port netdevs should trap to the bridge
 driver all IGMP join and leave messages.
 The bridge multicast module will notify port netdevs on every multicast group
 changed whether it is static configured or dynamically joined/leave.
 The hardware implementation should be forwarding all registered multicast
 traffic groups only to the configured ports.
 
 L3 Routing Offload
 ------------------
 
 Offloading L3 routing requires that device be programmed with FIB entries from
 the kernel, with the device doing the FIB lookup and forwarding.  The device
 does a longest prefix match (LPM) on FIB entries matching route prefix and
 forwards the packet to the matching FIB entry's nexthop(s) egress ports.
 
 To program the device, the driver has to register a FIB notifier handler
 using register_fib_notifier. The following events are available:
 
 ===================  ===================================================
 FIB_EVENT_ENTRY_ADD  used for both adding a new FIB entry to the device,
                      or modifying an existing entry on the device.
 FIB_EVENT_ENTRY_DEL  used for removing a FIB entry
 FIB_EVENT_RULE_ADD,
 FIB_EVENT_RULE_DEL   used to propagate FIB rule changes
 ===================  ===================================================
 
 FIB_EVENT_ENTRY_ADD and FIB_EVENT_ENTRY_DEL events pass::
 
         struct fib_entry_notifier_info {
                 struct fib_notifier_info info; /* must be first */
                 u32 dst;
                 int dst_len;
                 struct fib_info *fi;
                 u8 tos;
                 u8 type;
                 u32 tb_id;
                 u32 nlflags;
         };
 
 to add/modify/delete IPv4 dst/dest_len prefix on table tb_id.  The ``*fi``
 structure holds details on the route and route's nexthops.  ``*dev`` is one
 of the port netdevs mentioned in the route's next hop list.
 
 Routes offloaded to the device are labeled with "offload" in the ip route
 listing::
 
         $ ip route show
         default via 192.168.0.2 dev eth0
         11.0.0.0/30 dev sw1p1  proto kernel  scope link  src 11.0.0.2 offload
         11.0.0.4/30 via 11.0.0.1 dev sw1p1  proto zebra  metric 20 offload
         11.0.0.8/30 dev sw1p2  proto kernel  scope link  src 11.0.0.10 offload
         11.0.0.12/30 via 11.0.0.9 dev sw1p2  proto zebra  metric 20 offload
         12.0.0.2  proto zebra  metric 30 offload
                 nexthop via 11.0.0.1  dev sw1p1 weight 1
                 nexthop via 11.0.0.9  dev sw1p2 weight 1
         12.0.0.3 via 11.0.0.1 dev sw1p1  proto zebra  metric 20 offload
         12.0.0.4 via 11.0.0.9 dev sw1p2  proto zebra  metric 20 offload
         192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.15
 
 The "offload" flag is set in case at least one device offloads the FIB entry.
 
 XXX: add/mod/del IPv6 FIB API
 
 Nexthop Resolution
 ^^^^^^^^^^^^^^^^^^
 
 The FIB entry's nexthop list contains the nexthop tuple (gateway, dev), but for
 the switch device to forward the packet with the correct dst mac address, the
 nexthop gateways must be resolved to the neighbor's mac address.  Neighbor mac
 address discovery comes via the ARP (or ND) process and is available via the
 arp_tbl neighbor table.  To resolve the routes nexthop gateways, the driver
 should trigger the kernel's neighbor resolution process.  See the rocker
 driver's rocker_port_ipv4_resolve() for an example.
 
 The driver can monitor for updates to arp_tbl using the netevent notifier
 NETEVENT_NEIGH_UPDATE.  The device can be programmed with resolved nexthops
 for the routes as arp_tbl updates.  The driver implements ndo_neigh_destroy
 to know when arp_tbl neighbor entries are purged from the port.
 
 Device driver expected behavior
 -------------------------------
 
 Below is a set of defined behavior that switchdev enabled network devices must
 adhere to.
 
 Configuration-less state
 ^^^^^^^^^^^^^^^^^^^^^^^^
 
 Upon driver bring up, the network devices must be fully operational, and the
 backing driver must configure the network device such that it is possible to
 send and receive traffic to this network device and it is properly separated
 from other network devices/ports (e.g.: as is frequent with a switch ASIC). How
 this is achieved is heavily hardware dependent, but a simple solution can be to
 use per-port VLAN identifiers unless a better mechanism is available
 (proprietary metadata for each network port for instance).
 
 The network device must be capable of running a full IP protocol stack
 including multicast, DHCP, IPv4/6, etc. If necessary, it should program the
 appropriate filters for VLAN, multicast, unicast etc. The underlying device
 driver must effectively be configured in a similar fashion to what it would do
 when IGMP snooping is enabled for IP multicast over these switchdev network
 devices and unsolicited multicast must be filtered as early as possible in
 the hardware.
 
 When configuring VLANs on top of the network device, all VLANs must be working,
 irrespective of the state of other network devices (e.g.: other ports being part
 of a VLAN-aware bridge doing ingress VID checking). See below for details.
 
 If the device implements e.g.: VLAN filtering, putting the interface in
 promiscuous mode should allow the reception of all VLAN tags (including those
 not present in the filter(s)).
 
 Bridged switch ports
 ^^^^^^^^^^^^^^^^^^^^
 
 When a switchdev enabled network device is added as a bridge member, it should
 not disrupt any functionality of non-bridged network devices and they
 should continue to behave as normal network devices. Depending on the bridge
 configuration knobs below, the expected behavior is documented.
 
 Bridge VLAN filtering
 ^^^^^^^^^^^^^^^^^^^^^
 
 The Linux bridge allows the configuration of a VLAN filtering mode (statically,
 at device creation time, and dynamically, during run time) which must be
 observed by the underlying switchdev network device/hardware:
 
 - with VLAN filtering turned off: the bridge is strictly VLAN unaware and its
   data path will process all Ethernet frames as if they are VLAN-untagged.
   The bridge VLAN database can still be modified, but the modifications should
   have no effect while VLAN filtering is turned off. Frames ingressing the
   device with a VID that is not programmed into the bridge/switch's VLAN table
   must be forwarded and may be processed using a VLAN device (see below).
 
 - with VLAN filtering turned on: the bridge is VLAN-aware and frames ingressing
   the device with a VID that is not programmed into the bridges/switch's VLAN
   table must be dropped (strict VID checking).
 
 When there is a VLAN device (e.g: sw0p1.100) configured on top of a switchdev
 network device which is a bridge port member, the behavior of the software
 network stack must be preserved, or the configuration must be refused if that
 is not possible.
 
 - with VLAN filtering turned off, the bridge will process all ingress traffic
   for the port, except for the traffic tagged with a VLAN ID destined for a
   VLAN upper. The VLAN upper interface (which consumes the VLAN tag) can even
   be added to a second bridge, which includes other switch ports or software
   interfaces. Some approaches to ensure that the forwarding domain for traffic
   belonging to the VLAN upper interfaces are managed properly:
 
     * If forwarding destinations can be managed per VLAN, the hardware could be
       configured to map all traffic, except the packets tagged with a VID
       belonging to a VLAN upper interface, to an internal VID corresponding to
       untagged packets. This internal VID spans all ports of the VLAN-unaware
       bridge. The VID corresponding to the VLAN upper interface spans the
       physical port of that VLAN interface, as well as the other ports that
       might be bridged with it.
     * Treat bridge ports with VLAN upper interfaces as standalone, and let
       forwarding be handled in the software data path.
 
 - with VLAN filtering turned on, these VLAN devices can be created as long as
   the bridge does not have an existing VLAN entry with the same VID on any
   bridge port. These VLAN devices cannot be enslaved into the bridge since they
   duplicate functionality/use case with the bridge's VLAN data path processing.
 
 Non-bridged network ports of the same switch fabric must not be disturbed in any
 way by the enabling of VLAN filtering on the bridge device(s). If the VLAN
 filtering setting is global to the entire chip, then the standalone ports
 should indicate to the network stack that VLAN filtering is required by setting
 'rx-vlan-filter: on [fixed]' in the ethtool features.
 
 Because VLAN filtering can be turned on/off at runtime, the switchdev driver
 must be able to reconfigure the underlying hardware on the fly to honor the
 toggling of that option and behave appropriately. If that is not possible, the
 switchdev driver can also refuse to support dynamic toggling of the VLAN
 filtering knob at runtime and require a destruction of the bridge device(s) and
 creation of new bridge device(s) with a different VLAN filtering value to
 ensure VLAN awareness is pushed down to the hardware.
 
 Even when VLAN filtering in the bridge is turned off, the underlying switch
 hardware and driver may still configure itself in a VLAN-aware mode provided
 that the behavior described above is observed.
 
 The VLAN protocol of the bridge plays a role in deciding whether a packet is
 treated as tagged or not: a bridge using the 802.1ad protocol must treat both
 VLAN-untagged packets, as well as packets tagged with 802.1Q headers, as
 untagged.
 
 The 802.1p (VID 0) tagged packets must be treated in the same way by the device
 as untagged packets, since the bridge device does not allow the manipulation of
 VID 0 in its database.
 
 When the bridge has VLAN filtering enabled and a PVID is not configured on the
 ingress port, untagged and 802.1p tagged packets must be dropped. When the bridge
 has VLAN filtering enabled and a PVID exists on the ingress port, untagged and
 priority-tagged packets must be accepted and forwarded according to the
 bridge's port membership of the PVID VLAN. When the bridge has VLAN filtering
 disabled, the presence/lack of a PVID should not influence the packet
 forwarding decision.
 
 Bridge IGMP snooping
 ^^^^^^^^^^^^^^^^^^^^
 
 The Linux bridge allows the configuration of IGMP snooping (statically, at
 interface creation time, or dynamically, during runtime) which must be observed
 by the underlying switchdev network device/hardware in the following way:
 
 - when IGMP snooping is turned off, multicast traffic must be flooded to all
   ports within the same bridge that have mcast_flood=true. The CPU/management
   port should ideally not be flooded (unless the ingress interface has
   IFF_ALLMULTI or IFF_PROMISC) and continue to learn multicast traffic through
   the network stack notifications. If the hardware is not capable of doing that
   then the CPU/management port must also be flooded and multicast filtering
   happens in software.
 
 - when IGMP snooping is turned on, multicast traffic must selectively flow
   to the appropriate network ports (including CPU/management port). Flooding of
   unknown multicast should be only towards the ports connected to a multicast
   router (the local device may also act as a multicast router).
 
 The switch must adhere to RFC 4541 and flood multicast traffic accordingly
 since that is what the Linux bridge implementation does.
 
 Because IGMP snooping can be turned on/off at runtime, the switchdev driver
 must be able to reconfigure the underlying hardware on the fly to honor the
 toggling of that option and behave appropriately.
 
 A switchdev driver can also refuse to support dynamic toggling of the multicast
 snooping knob at runtime and require the destruction of the bridge device(s)
 and creation of a new bridge device(s) with a different multicast snooping
 value.

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