565 lines
25 KiB
ReStructuredText
565 lines
25 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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.. include:: <isonum.txt>
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.. _switchdev:
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===============================================
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Ethernet switch device driver model (switchdev)
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===============================================
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Copyright |copy| 2014 Jiri Pirko <jiri@resnulli.us>
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Copyright |copy| 2014-2015 Scott Feldman <sfeldma@gmail.com>
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The Ethernet switch device driver model (switchdev) is an in-kernel driver
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model for switch devices which offload the forwarding (data) plane from the
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kernel.
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Figure 1 is a block diagram showing the components of the switchdev model for
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an example setup using a data-center-class switch ASIC chip. Other setups
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with SR-IOV or soft switches, such as OVS, are possible.
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::
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User-space tools
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user space |
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+-------------------------------------------------------------------+
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kernel | Netlink
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+--------------+-------------------------------+
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| Network stack |
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| (Linux) |
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| |
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+----------------------------------------------+
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sw1p2 sw1p4 sw1p6
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sw1p1 + sw1p3 + sw1p5 + eth1
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+ | + | + | +
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| | | | | | |
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+--+----+----+----+----+----+---+ +-----+-----+
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| Switch driver | | mgmt |
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| (this document) | | driver |
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| | | |
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+--------------+----------------+ +-----------+
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kernel | HW bus (eg PCI)
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+-------------------------------------------------------------------+
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hardware |
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+--------------+----------------+
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| Switch device (sw1) |
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| +----+ +--------+
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| | v offloaded data path | mgmt port
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| | | |
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+--|----|----+----+----+----+---+
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| | | | | |
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+ + + + + +
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p1 p2 p3 p4 p5 p6
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front-panel ports
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Fig 1.
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Include Files
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-------------
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::
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#include <linux/netdevice.h>
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#include <net/switchdev.h>
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Configuration
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-------------
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Use "depends NET_SWITCHDEV" in driver's Kconfig to ensure switchdev model
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support is built for driver.
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Switch Ports
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------------
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On switchdev driver initialization, the driver will allocate and register a
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struct net_device (using register_netdev()) for each enumerated physical switch
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port, called the port netdev. A port netdev is the software representation of
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the physical port and provides a conduit for control traffic to/from the
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controller (the kernel) and the network, as well as an anchor point for higher
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level constructs such as bridges, bonds, VLANs, tunnels, and L3 routers. Using
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standard netdev tools (iproute2, ethtool, etc), the port netdev can also
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provide to the user access to the physical properties of the switch port such
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as PHY link state and I/O statistics.
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There is (currently) no higher-level kernel object for the switch beyond the
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port netdevs. All of the switchdev driver ops are netdev ops or switchdev ops.
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A switch management port is outside the scope of the switchdev driver model.
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Typically, the management port is not participating in offloaded data plane and
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is loaded with a different driver, such as a NIC driver, on the management port
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device.
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Switch ID
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^^^^^^^^^
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The switchdev driver must implement the net_device operation
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ndo_get_port_parent_id for each port netdev, returning the same physical ID for
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each port of a switch. The ID must be unique between switches on the same
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system. The ID does not need to be unique between switches on different
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systems.
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The switch ID is used to locate ports on a switch and to know if aggregated
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ports belong to the same switch.
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Port Netdev Naming
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^^^^^^^^^^^^^^^^^^
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Udev rules should be used for port netdev naming, using some unique attribute
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of the port as a key, for example the port MAC address or the port PHYS name.
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Hard-coding of kernel netdev names within the driver is discouraged; let the
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kernel pick the default netdev name, and let udev set the final name based on a
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port attribute.
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Using port PHYS name (ndo_get_phys_port_name) for the key is particularly
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useful for dynamically-named ports where the device names its ports based on
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external configuration. For example, if a physical 40G port is split logically
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into 4 10G ports, resulting in 4 port netdevs, the device can give a unique
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name for each port using port PHYS name. The udev rule would be::
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SUBSYSTEM=="net", ACTION=="add", ATTR{phys_switch_id}=="<phys_switch_id>", \
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ATTR{phys_port_name}!="", NAME="swX$attr{phys_port_name}"
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Suggested naming convention is "swXpYsZ", where X is the switch name or ID, Y
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is the port name or ID, and Z is the sub-port name or ID. For example, sw1p1s0
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would be sub-port 0 on port 1 on switch 1.
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Port Features
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^^^^^^^^^^^^^
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NETIF_F_NETNS_LOCAL
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If the switchdev driver (and device) only supports offloading of the default
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network namespace (netns), the driver should set this feature flag to prevent
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the port netdev from being moved out of the default netns. A netns-aware
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driver/device would not set this flag and be responsible for partitioning
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hardware to preserve netns containment. This means hardware cannot forward
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traffic from a port in one namespace to another port in another namespace.
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Port Topology
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^^^^^^^^^^^^^
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The port netdevs representing the physical switch ports can be organized into
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higher-level switching constructs. The default construct is a standalone
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router port, used to offload L3 forwarding. Two or more ports can be bonded
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together to form a LAG. Two or more ports (or LAGs) can be bridged to bridge
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L2 networks. VLANs can be applied to sub-divide L2 networks. L2-over-L3
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tunnels can be built on ports. These constructs are built using standard Linux
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tools such as the bridge driver, the bonding/team drivers, and netlink-based
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tools such as iproute2.
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The switchdev driver can know a particular port's position in the topology by
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monitoring NETDEV_CHANGEUPPER notifications. For example, a port moved into a
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bond will see its upper master change. If that bond is moved into a bridge,
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the bond's upper master will change. And so on. The driver will track such
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movements to know what position a port is in in the overall topology by
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registering for netdevice events and acting on NETDEV_CHANGEUPPER.
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L2 Forwarding Offload
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---------------------
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The idea is to offload the L2 data forwarding (switching) path from the kernel
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to the switchdev device by mirroring bridge FDB entries down to the device. An
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FDB entry is the {port, MAC, VLAN} tuple forwarding destination.
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To offloading L2 bridging, the switchdev driver/device should support:
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- Static FDB entries installed on a bridge port
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- Notification of learned/forgotten src mac/vlans from device
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- STP state changes on the port
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- VLAN flooding of multicast/broadcast and unknown unicast packets
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Static FDB Entries
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^^^^^^^^^^^^^^^^^^
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A driver which implements the ``ndo_fdb_add``, ``ndo_fdb_del`` and
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``ndo_fdb_dump`` operations is able to support the command below, which adds a
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static bridge FDB entry::
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bridge fdb add dev DEV ADDRESS [vlan VID] [self] static
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(the "static" keyword is non-optional: if not specified, the entry defaults to
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being "local", which means that it should not be forwarded)
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The "self" keyword (optional because it is implicit) has the role of
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instructing the kernel to fulfill the operation through the ``ndo_fdb_add``
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implementation of the ``DEV`` device itself. If ``DEV`` is a bridge port, this
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will bypass the bridge and therefore leave the software database out of sync
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with the hardware one.
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To avoid this, the "master" keyword can be used::
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bridge fdb add dev DEV ADDRESS [vlan VID] master static
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The above command instructs the kernel to search for a master interface of
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``DEV`` and fulfill the operation through the ``ndo_fdb_add`` method of that.
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This time, the bridge generates a ``SWITCHDEV_FDB_ADD_TO_DEVICE`` notification
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which the port driver can handle and use it to program its hardware table. This
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way, the software and the hardware database will both contain this static FDB
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entry.
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Note: for new switchdev drivers that offload the Linux bridge, implementing the
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``ndo_fdb_add`` and ``ndo_fdb_del`` bridge bypass methods is strongly
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discouraged: all static FDB entries should be added on a bridge port using the
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"master" flag. The ``ndo_fdb_dump`` is an exception and can be implemented to
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visualize the hardware tables, if the device does not have an interrupt for
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notifying the operating system of newly learned/forgotten dynamic FDB
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addresses. In that case, the hardware FDB might end up having entries that the
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software FDB does not, and implementing ``ndo_fdb_dump`` is the only way to see
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them.
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Note: by default, the bridge does not filter on VLAN and only bridges untagged
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traffic. To enable VLAN support, turn on VLAN filtering::
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echo 1 >/sys/class/net/<bridge>/bridge/vlan_filtering
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Notification of Learned/Forgotten Source MAC/VLANs
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The switch device will learn/forget source MAC address/VLAN on ingress packets
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and notify the switch driver of the mac/vlan/port tuples. The switch driver,
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in turn, will notify the bridge driver using the switchdev notifier call::
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err = call_switchdev_notifiers(val, dev, info, extack);
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Where val is SWITCHDEV_FDB_ADD when learning and SWITCHDEV_FDB_DEL when
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forgetting, and info points to a struct switchdev_notifier_fdb_info. On
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SWITCHDEV_FDB_ADD, the bridge driver will install the FDB entry into the
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bridge's FDB and mark the entry as NTF_EXT_LEARNED. The iproute2 bridge
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command will label these entries "offload"::
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$ bridge fdb
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52:54:00:12:35:01 dev sw1p1 master br0 permanent
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00:02:00:00:02:00 dev sw1p1 master br0 offload
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00:02:00:00:02:00 dev sw1p1 self
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52:54:00:12:35:02 dev sw1p2 master br0 permanent
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00:02:00:00:03:00 dev sw1p2 master br0 offload
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00:02:00:00:03:00 dev sw1p2 self
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33:33:00:00:00:01 dev eth0 self permanent
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01:00:5e:00:00:01 dev eth0 self permanent
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33:33:ff:00:00:00 dev eth0 self permanent
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01:80:c2:00:00:0e dev eth0 self permanent
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33:33:00:00:00:01 dev br0 self permanent
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01:00:5e:00:00:01 dev br0 self permanent
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33:33:ff:12:35:01 dev br0 self permanent
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Learning on the port should be disabled on the bridge using the bridge command::
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bridge link set dev DEV learning off
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Learning on the device port should be enabled, as well as learning_sync::
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bridge link set dev DEV learning on self
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bridge link set dev DEV learning_sync on self
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Learning_sync attribute enables syncing of the learned/forgotten FDB entry to
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the bridge's FDB. It's possible, but not optimal, to enable learning on the
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device port and on the bridge port, and disable learning_sync.
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To support learning, the driver implements switchdev op
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switchdev_port_attr_set for SWITCHDEV_ATTR_PORT_ID_{PRE}_BRIDGE_FLAGS.
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FDB Ageing
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^^^^^^^^^^
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The bridge will skip ageing FDB entries marked with NTF_EXT_LEARNED and it is
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the responsibility of the port driver/device to age out these entries. If the
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port device supports ageing, when the FDB entry expires, it will notify the
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driver which in turn will notify the bridge with SWITCHDEV_FDB_DEL. If the
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device does not support ageing, the driver can simulate ageing using a
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garbage collection timer to monitor FDB entries. Expired entries will be
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notified to the bridge using SWITCHDEV_FDB_DEL. See rocker driver for
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example of driver running ageing timer.
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To keep an NTF_EXT_LEARNED entry "alive", the driver should refresh the FDB
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entry by calling call_switchdev_notifiers(SWITCHDEV_FDB_ADD, ...). The
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notification will reset the FDB entry's last-used time to now. The driver
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should rate limit refresh notifications, for example, no more than once a
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second. (The last-used time is visible using the bridge -s fdb option).
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STP State Change on Port
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^^^^^^^^^^^^^^^^^^^^^^^^
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Internally or with a third-party STP protocol implementation (e.g. mstpd), the
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bridge driver maintains the STP state for ports, and will notify the switch
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driver of STP state change on a port using the switchdev op
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switchdev_attr_port_set for SWITCHDEV_ATTR_PORT_ID_STP_UPDATE.
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State is one of BR_STATE_*. The switch driver can use STP state updates to
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update ingress packet filter list for the port. For example, if port is
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DISABLED, no packets should pass, but if port moves to BLOCKED, then STP BPDUs
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and other IEEE 01:80:c2:xx:xx:xx link-local multicast packets can pass.
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Note that STP BDPUs are untagged and STP state applies to all VLANs on the port
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so packet filters should be applied consistently across untagged and tagged
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VLANs on the port.
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Flooding L2 domain
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^^^^^^^^^^^^^^^^^^
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For a given L2 VLAN domain, the switch device should flood multicast/broadcast
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and unknown unicast packets to all ports in domain, if allowed by port's
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current STP state. The switch driver, knowing which ports are within which
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vlan L2 domain, can program the switch device for flooding. The packet may
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be sent to the port netdev for processing by the bridge driver. The
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bridge should not reflood the packet to the same ports the device flooded,
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otherwise there will be duplicate packets on the wire.
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To avoid duplicate packets, the switch driver should mark a packet as already
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forwarded by setting the skb->offload_fwd_mark bit. The bridge driver will mark
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the skb using the ingress bridge port's mark and prevent it from being forwarded
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through any bridge port with the same mark.
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It is possible for the switch device to not handle flooding and push the
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packets up to the bridge driver for flooding. This is not ideal as the number
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of ports scale in the L2 domain as the device is much more efficient at
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flooding packets that software.
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If supported by the device, flood control can be offloaded to it, preventing
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certain netdevs from flooding unicast traffic for which there is no FDB entry.
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IGMP Snooping
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^^^^^^^^^^^^^
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In order to support IGMP snooping, the port netdevs should trap to the bridge
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driver all IGMP join and leave messages.
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The bridge multicast module will notify port netdevs on every multicast group
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changed whether it is static configured or dynamically joined/leave.
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The hardware implementation should be forwarding all registered multicast
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traffic groups only to the configured ports.
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L3 Routing Offload
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------------------
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Offloading L3 routing requires that device be programmed with FIB entries from
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the kernel, with the device doing the FIB lookup and forwarding. The device
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does a longest prefix match (LPM) on FIB entries matching route prefix and
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forwards the packet to the matching FIB entry's nexthop(s) egress ports.
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To program the device, the driver has to register a FIB notifier handler
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using register_fib_notifier. The following events are available:
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=================== ===================================================
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FIB_EVENT_ENTRY_ADD used for both adding a new FIB entry to the device,
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or modifying an existing entry on the device.
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FIB_EVENT_ENTRY_DEL used for removing a FIB entry
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FIB_EVENT_RULE_ADD,
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FIB_EVENT_RULE_DEL used to propagate FIB rule changes
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=================== ===================================================
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FIB_EVENT_ENTRY_ADD and FIB_EVENT_ENTRY_DEL events pass::
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struct fib_entry_notifier_info {
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struct fib_notifier_info info; /* must be first */
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u32 dst;
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int dst_len;
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struct fib_info *fi;
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u8 tos;
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u8 type;
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u32 tb_id;
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u32 nlflags;
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};
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to add/modify/delete IPv4 dst/dest_len prefix on table tb_id. The ``*fi``
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structure holds details on the route and route's nexthops. ``*dev`` is one
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of the port netdevs mentioned in the route's next hop list.
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Routes offloaded to the device are labeled with "offload" in the ip route
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listing::
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$ ip route show
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default via 192.168.0.2 dev eth0
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11.0.0.0/30 dev sw1p1 proto kernel scope link src 11.0.0.2 offload
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11.0.0.4/30 via 11.0.0.1 dev sw1p1 proto zebra metric 20 offload
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11.0.0.8/30 dev sw1p2 proto kernel scope link src 11.0.0.10 offload
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11.0.0.12/30 via 11.0.0.9 dev sw1p2 proto zebra metric 20 offload
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12.0.0.2 proto zebra metric 30 offload
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nexthop via 11.0.0.1 dev sw1p1 weight 1
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nexthop via 11.0.0.9 dev sw1p2 weight 1
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12.0.0.3 via 11.0.0.1 dev sw1p1 proto zebra metric 20 offload
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12.0.0.4 via 11.0.0.9 dev sw1p2 proto zebra metric 20 offload
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192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.15
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The "offload" flag is set in case at least one device offloads the FIB entry.
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XXX: add/mod/del IPv6 FIB API
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Nexthop Resolution
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^^^^^^^^^^^^^^^^^^
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The FIB entry's nexthop list contains the nexthop tuple (gateway, dev), but for
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the switch device to forward the packet with the correct dst mac address, the
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nexthop gateways must be resolved to the neighbor's mac address. Neighbor mac
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address discovery comes via the ARP (or ND) process and is available via the
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arp_tbl neighbor table. To resolve the routes nexthop gateways, the driver
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should trigger the kernel's neighbor resolution process. See the rocker
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driver's rocker_port_ipv4_resolve() for an example.
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The driver can monitor for updates to arp_tbl using the netevent notifier
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NETEVENT_NEIGH_UPDATE. The device can be programmed with resolved nexthops
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for the routes as arp_tbl updates. The driver implements ndo_neigh_destroy
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to know when arp_tbl neighbor entries are purged from the port.
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Device driver expected behavior
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-------------------------------
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Below is a set of defined behavior that switchdev enabled network devices must
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adhere to.
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Configuration-less state
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^^^^^^^^^^^^^^^^^^^^^^^^
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Upon driver bring up, the network devices must be fully operational, and the
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backing driver must configure the network device such that it is possible to
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send and receive traffic to this network device and it is properly separated
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from other network devices/ports (e.g.: as is frequent with a switch ASIC). How
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this is achieved is heavily hardware dependent, but a simple solution can be to
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use per-port VLAN identifiers unless a better mechanism is available
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(proprietary metadata for each network port for instance).
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The network device must be capable of running a full IP protocol stack
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including multicast, DHCP, IPv4/6, etc. If necessary, it should program the
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appropriate filters for VLAN, multicast, unicast etc. The underlying device
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driver must effectively be configured in a similar fashion to what it would do
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when IGMP snooping is enabled for IP multicast over these switchdev network
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devices and unsolicited multicast must be filtered as early as possible in
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the hardware.
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When configuring VLANs on top of the network device, all VLANs must be working,
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irrespective of the state of other network devices (e.g.: other ports being part
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of a VLAN-aware bridge doing ingress VID checking). See below for details.
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If the device implements e.g.: VLAN filtering, putting the interface in
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promiscuous mode should allow the reception of all VLAN tags (including those
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not present in the filter(s)).
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Bridged switch ports
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^^^^^^^^^^^^^^^^^^^^
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When a switchdev enabled network device is added as a bridge member, it should
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not disrupt any functionality of non-bridged network devices and they
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should continue to behave as normal network devices. Depending on the bridge
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configuration knobs below, the expected behavior is documented.
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Bridge VLAN filtering
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^^^^^^^^^^^^^^^^^^^^^
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The Linux bridge allows the configuration of a VLAN filtering mode (statically,
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at device creation time, and dynamically, during run time) which must be
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observed by the underlying switchdev network device/hardware:
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|
|
|
- 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).
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|
|
|
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.
|