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Date: Sat, 17 Aug 2019 16:28:19 +0300
From: Ido Schimmel <idosch@...sch.org>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net, nhorman@...driver.com, jiri@...lanox.com,
toke@...hat.com, dsahern@...il.com, roopa@...ulusnetworks.com,
nikolay@...ulusnetworks.com, jakub.kicinski@...ronome.com,
andy@...yhouse.net, f.fainelli@...il.com, andrew@...n.ch,
vivien.didelot@...il.com, mlxsw@...lanox.com,
Ido Schimmel <idosch@...lanox.com>
Subject: [PATCH net-next v3 10/16] 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>
Acked-by: Jiri Pirko <jiri@...lanox.com>
---
Documentation/networking/devlink-trap.rst | 187 ++++++++++++++++++++++
Documentation/networking/index.rst | 1 +
include/net/devlink.h | 6 +
3 files changed, 194 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..dbc7a3e00fd8
--- /dev/null
+++ b/Documentation/networking/devlink-trap.rst
@@ -0,0 +1,187 @@
+.. 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
+ Or a summary of recent drops
+ ^
+ |
+ Userspace |
+ +---------------------------------------------------+
+ Kernel |
+ |
+ +-------+--------+
+ | |
+ | drop_monitor |
+ | |
+ +-------^--------+
+ |
+ |
+ |
+ +----+----+
+ | | 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
+ * - ``source_mac_is_multicast``
+ - ``drop``
+ - Traps incoming packets that the device decided to drop because of a
+ multicast source MAC
+ * - ``vlan_tag_mismatch``
+ - ``drop``
+ - Traps incoming packets that the device decided to drop in case of VLAN
+ tag mismatch: The ingress bridge port is not configured with a PVID and
+ the packet is untagged or prio-tagged
+ * - ``ingress_vlan_filter``
+ - ``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_spanning_tree_filter``
+ - ``drop``
+ - Traps incoming packets that the device decided to drop in case the STP
+ state of the ingress bridge port is not "forwarding"
+ * - ``port_list_is_empty``
+ - ``drop``
+ - Traps packets that the device decided to drop in case they need to be
+ flooded and the flood list is empty
+ * - ``port_loopback_filter``
+ - ``drop``
+ - Traps packets 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``
+ - Traps packets that the device decided to drop in case they hit a
+ blackhole route
+ * - ``ttl_value_is_too_small``
+ - ``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
+
+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 of all member traps. In addition, ``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 a46fca264bee..86a814e4d450 100644
--- a/Documentation/networking/index.rst
+++ b/Documentation/networking/index.rst
@@ -14,6 +14,7 @@ Contents:
device_drivers/index
dsa/index
devlink-info-versions
+ devlink-trap
ieee802154
kapi
z8530book
diff --git a/include/net/devlink.h b/include/net/devlink.h
index fb02e0e89f9d..7f43c48f54cd 100644
--- a/include/net/devlink.h
+++ b/include/net/devlink.h
@@ -540,6 +540,9 @@ 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_SMAC_MC,
DEVLINK_TRAP_GENERIC_ID_VLAN_TAG_MISMATCH,
@@ -556,6 +559,9 @@ 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,
--
2.21.0
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