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Message-Id: <20190528122136.30476-5-idosch@idosch.org> Date: Tue, 28 May 2019 15:21:28 +0300 From: Ido Schimmel <idosch@...sch.org> To: netdev@...r.kernel.org Cc: davem@...emloft.net, jiri@...lanox.com, mlxsw@...lanox.com, dsahern@...il.com, roopa@...ulusnetworks.com, nikolay@...ulusnetworks.com, andy@...yhouse.net, pablo@...filter.org, jakub.kicinski@...ronome.com, pieter.jansenvanvuuren@...ronome.com, andrew@...n.ch, f.fainelli@...il.com, vivien.didelot@...oirfairelinux.com, Ido Schimmel <idosch@...lanox.com> Subject: [RFC PATCH net-next 04/12] Documentation: Add devlink-trap documentation From: Ido Schimmel <idosch@...lanox.com> Add initial documentation of the devlink-trap mechanism, explaining the background, motivation and the semantics of the interface. Signed-off-by: Ido Schimmel <idosch@...lanox.com> --- Documentation/networking/devlink-trap.rst | 189 ++++++++++++++++++++++ Documentation/networking/index.rst | 1 + include/net/devlink.h | 6 + 3 files changed, 196 insertions(+) create mode 100644 Documentation/networking/devlink-trap.rst diff --git a/Documentation/networking/devlink-trap.rst b/Documentation/networking/devlink-trap.rst new file mode 100644 index 000000000000..4b3045bc76d1 --- /dev/null +++ b/Documentation/networking/devlink-trap.rst @@ -0,0 +1,189 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============ +Devlink Trap +============ + +Background +========== + +Devices capable of offloading the kernel's datapath and perform functions such +as bridging and routing must also be able to send specific packets to the +kernel (i.e., the CPU) for processing. + +For example, a device acting as a multicast-aware bridge must be able to send +IGMP membership reports to the kernel for processing by the bridge module. +Without processing such packets, the bridge module could never populate its +MDB. + +As another example, consider a device acting as router which has received an IP +packet with a TTL of 1. Upon routing the packet the device must send it to the +kernel so that it will route it as well and generate an ICMP Time Exceeded +error datagram. Without letting the kernel route such packets itself, utilities +such as ``traceroute`` could never work. + +The fundamental ability of sending certain packets to the kernel for processing +is called "packet trapping". + +Overview +======== + +The ``devlink-trap`` mechanism allows capable device drivers to register their +supported packet traps with ``devlink`` and report trapped packets to +``devlink`` for further analysis. + +Upon receiving trapped packets, ``devlink`` will perform a per-trap packets and +bytes accounting and potentially report the packet to user space via a netlink +event along with all the provided metadata (e.g., trap reason, timestamp, input +port). This is especially useful for drop traps (see :ref:`Trap-Types`) +as it allows users to obtain further visibility into packet drops that would +otherwise be invisible. + +The following diagram provides a general overview of ``devlink-trap``:: + + Netlink event: Packet w/ metadata + ^ + | + Userspace | + +---------------------------------------------------+ + Kernel | + | + +----+----+ + | | Kernel's Rx path + | devlink | (non-drop traps) + | | + +----^----+ ^ + | | + +-----------+ + | + +-------+-------+ + | | + | Device driver | + | | + +-------^-------+ + Kernel | + +---------------------------------------------------+ + Hardware | + | Trapped packet + | + +--+---+ + | | + | ASIC | + | | + +------+ + +.. _Trap-Types: + +Trap Types +========== + +The ``devlink-trap`` mechanism supports the following packet trap types: + + * ``drop``: Trapped packets were dropped by the underlying device. Packets + are only processed by ``devlink`` and not injected to the kernel's Rx path. + The trap action (see :ref:`Trap-Actions`) can be changed. + * ``exception``: Trapped packets were not forwarded as intended by the + underlying device due to an exception (e.g., TTL error, missing neighbour + entry) and trapped to the control plane for resolution. Packets are + processed by ``devlink`` and injected to the kernel's Rx path. Changing the + action of such traps is not allowed, as it can easily break the control + plane. + +.. _Trap-Actions: + +Trap Actions +============ + +The ``devlink-trap`` mechanism supports the following packet trap actions: + + * ``trap``: The sole copy of the packet is sent to the CPU. + * ``drop``: The packet is dropped by the underlying device and a copy is not + sent to the CPU. + +Generic Packet Traps +==================== + +Generic packet traps are used to describe traps that trap well-defined packets +or packets that are trapped due to well-defined conditions (e.g., TTL error). +Such traps can be shared by multiple device drivers and their description must +be added to the following table: + +.. list-table:: List of Generic Packet Traps + :widths: 5 5 90 + + * - Name + - Type + - Description + * - ``ingress_smac_mc_drop`` + - ``drop`` + - Traps incoming packets that the device decided to drop because of a + multicast source MAC + * - ``ingress_vlan_tag_allow_drop`` + - ``drop`` + - Traps incoming packets that the device decided to drop in case the + ingress bridge port is not configured with a PVID and the packet is + untagged or prio-tagged + * - ``ingress_vlan_filter_drop`` + - ``drop`` + - Traps incoming packets that the device decided to drop in case they are + tagged with a VLAN that is not configured on the ingress bridge port + * - ``ingress_stp_filter_drop`` + - ``drop`` + - Traps incoming packets that the device decided to drop in case the STP + state of the ingress bridge port is "listening", "disabled" or + "blocking" + * - ``uc_empty_tx_list_drop`` + - ``drop`` + - Traps packets with a unicast MAC that the device decided to drop in case + they need to be flooded and the flood list is empty + * - ``mc_empty_tx_list_drop`` + - ``drop`` + - Traps packets with a multicast MAC that the device decided to drop in + case they need to be flooded and the flood list is empty + * - ``uc_loopback_filter_drop`` + - ``drop`` + - Traps packets with a unicast MAC that the device decided to drop in case + after layer 2 forwarding the only port from which they should be + transmitted through is the port from which they were received + * - ``blackhole_route_drop`` + - ``drop`` + - Traps packets that the device decided to drop in case they hit a + blackhole route + * - ``ttl_error_exception`` + - ``exception`` + - Traps unicast packets that should be forwarded by the device whose TTL + was decremented to 0 or less + * - ``tail_drop`` + - ``drop`` + - Traps packets that the device decided to drop because they could not be + enqueued to a transmission queue which is full + * - ``early_drop`` + - ``drop`` + - Traps packets that the device decided to drop due to the decision of the + Random Early Detection (RED) queueing discipline to earlydrop the + packet + +Generic Packet Trap Groups +========================== + +Generic packet trap groups are used to aggregate logically related packet +traps. These groups allow the user to batch operations such as setting the +trap action and report state of all member traps. In addtion, ``devlink-trap`` +can report aggregated per-group packets and bytes statistics, in case per-trap +statistics are too narrow. The description of these groups must be added to the +following table: + +.. list-table:: List of Generic Packet Trap Groups + :widths: 10 90 + + * - Name + - Description + * - ``l2_drops`` + - Contains packet traps for packets that were dropped by the device during + layer 2 forwarding (i.e., bridge) + * - ``l3_drops`` + - Contains packet traps for packets that were dropped by the device or hit + an exception (e.g., TTL error) during layer 3 forwarding + * - ``buffer_drops`` + - Contains packet traps for packets that were dropped by the device due to + an enqueue decision diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst index f390fe3cfdfb..c09bf85ec050 100644 --- a/Documentation/networking/index.rst +++ b/Documentation/networking/index.rst @@ -26,6 +26,7 @@ Contents: device_drivers/intel/ice dsa/index devlink-info-versions + devlink-trap ieee802154 kapi z8530book diff --git a/include/net/devlink.h b/include/net/devlink.h index 6cfa1ab36e3f..4e095a70b466 100644 --- a/include/net/devlink.h +++ b/include/net/devlink.h @@ -524,6 +524,9 @@ struct devlink_trap { u32 metadata_cap; }; +/* All traps must be documented in + * Documentation/networking/devlink-trap.rst + */ enum devlink_trap_generic_id { DEVLINK_TRAP_GENERIC_ID_INGRESS_SMAC_MC_DROP, DEVLINK_TRAP_GENERIC_ID_INGRESS_VLAN_TAG_ALLOW_DROP, @@ -542,6 +545,9 @@ enum devlink_trap_generic_id { DEVLINK_TRAP_GENERIC_ID_MAX = __DEVLINK_TRAP_GENERIC_ID_MAX - 1, }; +/* All trap groups must be documented in + * Documentation/networking/devlink-trap.rst + */ enum devlink_trap_group_generic_id { DEVLINK_TRAP_GROUP_GENERIC_ID_L2_DROPS, DEVLINK_TRAP_GROUP_GENERIC_ID_L3_DROPS, -- 2.20.1
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