Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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diff --git a/Documentation/networking/switchdev.rst b/Documentation/networking/switchdev.rst
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+.. SPDX-License-Identifier: GPL-2.0
+.. include:: <isonum.txt>
+.. _switchdev:
+
+===============================================
+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.