doca-eth

# DOCA Ethernet

**Where to start:** This skill assumes DOCA is already installed and
the user is doing **hands-on packet-queue work** on a host or
BlueField with DOCA. Open [`TASKS.md`](TASKS.md) if the user wants
to *do* something (configure / build / modify / run / test /
debug); open [`CAPABILITIES.md`](CAPABILITIES.md) when the question
is *what can a DOCA Ethernet queue express* on this version. If
the user has not installed DOCA yet, route to
[`doca-setup`](../../doca-setup/SKILL.md) first. If the user is
asking *"how do I get packets to land on my RX queue at all"*, the
answer lives in [`doca-flow`](../doca-flow/SKILL.md) — DOCA
Ethernet is the *queue* surface; DOCA Flow is the *steering*
surface, and they are independent libraries.

## Example questions this skill answers well

The CLASSES of DOCA Ethernet questions this skill is built to
answer, each with one worked example. The agent should treat the
*class* as the load-bearing piece — the worked example is a single
instance.

- **"How do I bring up an RX and TX queue on a representor or
  physical port?"** — worked example: *"set up a `doca_eth_rxq`
  plus a `doca_eth_txq` on a single BlueField representor for
  first-run testing"*. Answered by the queue-pair lifecycle in
  [`TASKS.md ## configure`](TASKS.md#configure) +
  [`CAPABILITIES.md ## Capabilities and modes`](CAPABILITIES.md#capabilities-and-modes)
  RX / TX object table.
- **"Which RX type fits my data shape — regular, cyclic, or
  managed-recv?"** — worked example: *"line-rate ingress with
  fixed-size frames into a pre-allocated buffer ring"*. Answered
  by the RX-type taxonomy in
  [`CAPABILITIES.md ## Capabilities and modes`](CAPABILITIES.md#capabilities-and-modes)
  + the capability-query rule (`doca_eth_rxq_cap_is_type_supported`
  against a `doca_devinfo`) in
  [`TASKS.md ## configure`](TASKS.md#configure).
- **"How do I send a packet from user code through `doca_eth_txq`?"**
  — worked example: *"allocate a packet `doca_buf`, attach the
  payload, submit one send-task, wait for the completion event"*.
  Answered by the TX submission shape in
  [`CAPABILITIES.md ## Capabilities and modes`](CAPABILITIES.md#capabilities-and-modes)
  + the property-set workflow in
  [`TASKS.md ## modify`](TASKS.md#modify).
- **"My queue is up but no packets arrive — why?"** — worked
  example: *"`doca_eth_rxq` started cleanly but the recv callback
  never fires"*. Answered by the steering-dependency rule in
  [`CAPABILITIES.md ## Safety policy`](CAPABILITIES.md#safety-policy)
  + the env-prep checklist in
  [`TASKS.md ## configure`](TASKS.md#configure) step 1, which
  routes the steering side to
  [`doca-flow`](../doca-flow/SKILL.md) and the
  promiscuous-mode side to
  [`doca-setup`](../../doca-setup/SKILL.md).
- **"Is this Ethernet capability available on my device + my
  installed DOCA?"** — worked example: *"does this device
  advertise L3 checksum offload"*. Answered by the
  capability-query rule (`doca_eth_txq_cap_is_l3_chksum_offload_supported`
  against a `doca_devinfo`) in
  [`CAPABILITIES.md ## Capabilities and modes`](CAPABILITIES.md#capabilities-and-modes)
  + the version-and-device overlay in
  [`CAPABILITIES.md ## Version compatibility`](CAPABILITIES.md#version-compatibility).
- **"What does this `DOCA_ERROR_*` from an Ethernet call mean and
  which layer caused it?"** — worked example: *"`DOCA_ERROR_AGAIN`
  on `doca_task_submit` for an `eth_txq` send-task at high rate"*.
  Answered by the Ethernet overlay on the cross-library taxonomy
  in
  [`CAPABILITIES.md ## Error taxonomy`](CAPABILITIES.md#error-taxonomy)
  + the layered ladder in
  [`TASKS.md ## debug`](TASKS.md#debug) that escalates to
  [`doca-debug`](../../doca-debug/SKILL.md).

## Audience

This skill serves **external developers building applications that
consume the DOCA Ethernet library** — i.e., users whose code calls
`doca_eth_rxq_*` / `doca_eth_txq_*` (directly in C/C++, or through
FFI/bindings from another language) to do line-rate packet I/O on
physical ports, representors, or SFs of a BlueField or ConnectX
device. It is *not* for NVIDIA developers contributing to DOCA
Ethernet itself.

**Language scope.** DOCA Ethernet ships as a C library with
`pkg-config` module name `doca-eth`. The shipped samples are
written in C. C and C++ consumers are the canonical case; the
worked examples in `TASKS.md` assume that path. Other-language
consumers (Rust, Go, Python, …) consume the same `*.so` through
FFI or language-specific bindings; the skill's contribution in
that case is to keep the queue-object split, lifecycle,
capability-discovery, permission, RX-type taxonomy, and
error-taxonomy guidance language-neutral, and to route the agent
to the public C ABI as the authoritative surface that any wrapper
will eventually call.

## When to load this skill

Load this skill when the user is doing hands-on DOCA Ethernet
work, in any language. Concretely:

- Initializing a `doca_eth_rxq` on a `doca_dev` opened against a
  physical port, a representor, or an SF — choosing among the
  regular / cyclic / managed-recv RX types based on data shape
  before `doca_ctx_start()`.
- Initializing a `doca_eth_txq` on the same or a different
  `doca_dev` and posting send-tasks against packet `doca_buf`s
  payload buffers.
- Reading or setting Ethernet queue properties via
  `doca_eth_rxq_set_*` / `doca_eth_txq_set_*` and querying device
  capability via `doca_eth_rxq_cap_*` / `doca_eth_txq_cap_*`
  (max burst size, RX-type support, max scatter-gather length,
  checksum-offload presence).
- Confirming the port is up and that traffic is actually steered
  to the chosen RX queue — either via DOCA Flow rules (the
  canonical path) or via kernel-side promiscuous mode (the
  expedient first-run path).
- Wiring an Ethernet queue to a higher-level data plane: GPU
  packet processing via DOCA GPUNetIO, custom user-space
  forwarding agents, or telemetry mirrors that snap a copy of
  every packet.
- Debugging a `DOCA_ERROR_*` returned