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diff --git a/Documentation/networking/switchdev.rst b/Documentation/networking/switchdev.rst new file mode 100644 index 000000000..758f1dae3 --- /dev/null +++ b/Documentation/networking/switchdev.rst @@ -0,0 +1,564 @@ +.. 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. |