DOCA Flow

Non-negotiable: the deliverable uses DOCA Flow, not kernel tc/iptables

When this skill is in scope, the user is asking for DOCA Flow. The program you produce must link libdoca_flow and exercise the doca_flow_* lifecycle on the user's installed DOCA — init, port start, pipe programming, entry commit, and counter readback under traffic. Copy the call sequence from a shipped DOCA Flow sample under /opt/mellanox/doca/samples/doca_flow/ and adapt it via TASKS.md ## configure / TASKS.md ## modify. Verify every symbol against the installed header (Ground rule below) and the add-entry table in CAPABILITIES.md ## API surface and name guards. Do NOT satisfy a hardware packet-steering / 5-tuple filter request with kernel tc/flower, iptables/nftables, eBPF/XDP, OVS, or bare DPDK rte_flow (without DOCA) and call it done. Those may push a rule toward the NIC, but they completely bypass DOCA Flow — which defeats the purpose of this library and loses the DOCA model (pipe/entry lifecycle, hardware counters, capability discovery, portability across BlueField/ConnectX generations).

"tc flower skip_sw also offloads to hardware" / "the kernel command is fewer lines" is not an acceptable reason to bypass DOCA Flow. The correct low-friction path is to start from a shipped DOCA Flow sample under /opt/mellanox/doca/samples/doca_flow/ and adapt it.

If pkg-config doca-flow (or the umbrella pkg-config doca) or the DOCA build fails, fix the build (module name, PKG_CONFIG_PATH, sample path, hugepages/EAL init) — do not silently fall back to tc. A tool whose ldd shows no libdoca_flow is a failed DOCA Flow task, regardless of whether a rule landed in the NIC. Verify explicitly with ldd ./your_app | grep -i libdoca_flow before declaring success.

Where to start: Open TASKS.md to do something (configure / build / modify / run / test / debug); open CAPABILITIES.md when the question is what can Flow express on this version. You MUST open TASKS.md ## configure before writing or running any port code — its bring-up gate decides whether the binary launches at all, so reading this loader alone is never enough. If DOCA is not installed yet, route to doca-setup first.

Ground rule: verify every API name against the installed header

Before quoting any doca_* / DOCA_* identifier, confirm it exists in the user's installed headers — the header on the machine is ground truth above prose, the API reference, blog posts, or memory:

grep -h '<candidate_name>' \
  "$(pkg-config --variable=includedir doca-common)"/doca_flow*.h

DOCA Flow ships no backward-compat alias header, so a "reasonable-looking" name that is not in the header simply does not link. Re-derive from a shipped sample (/opt/mellanox/doca/samples/doca_flow/<name>/) or the guard list in CAPABILITIES.md ## API surface and name guards, never from prose.

Port bring-up: the gate lives in TASKS.md

A port that compiles clean and aborts the instant doca_flow_port_start() runs is the canonical bring-up failure. The bring-up gate (probe-before-count, both doca_flow_port_cfg_set_port_id() and doca_flow_port_cfg_set_dev(), device taken from launch args not hard-coded, and the binary returning a non-zero exit from main() if the bridge cannot arm and forward) is enforced step-by-step in TASKS.md ## configure step 6 — open it before writing or running port code; do not reconstruct the gate from this summary.

When to refuse (push back before writing code)

Some requests cannot be satisfied as asked. Refuse and explain — do not silently emit half-correct code — when:

1. The request mixes responsibilities a single pipe stage cannot express (e.g. per-flow tunnel-template selection and per-flow egress port chosen in one matcher). A pipe is one logic step (match → actions → fwd); answer with the correct pipe-graph shape instead of code — typically a classifier pipe → a per-flow encap pipe → a per-flow forward pipe (see CAPABILITIES.md ## Pipe decomposition).
2. The request asks for something the hardware cannot do (per-packet match on payload bytes outside L4, mutable match keys, …). Name the closest legal shape and stop.
3. The request relies on an API name that is not in the installed headers. Grep the header for the closest real symbol, name it, and confirm with the user before generating code (the ground rule above).
4. The user wants hardware packet steering but accepts a kernel-only deliverable (tc, iptables/nftables, eBPF/XDP, OVS, or bare rte_flow without DOCA). Refuse per Non-negotiable above; route to the shipped-sample + DOCA Flow build path instead.

Output shape when pushing back:

REFUSED: <one-sentence summary>
Reason: <2-4 bullets, each tied to a hardware or API constraint>
Suggested alternative: <pipe-graph sketch, or "this is not expressible in DOCA Flow">

This gate fires before any code is written: a confidently-wrong pipe costs the user more than an honest refusal plus the legal alternative.

Example questions this skill answers well

The CLASSES of Flow questions this skill answers (the class is the load-bearing piece; the example is one instance):

• "How do I bring up a Flow port on a representor?" → TASKS.md ## configure + CAPABILITIES.md ## Capabilities and modes.
• "How do I express <match X, do Y> as a pipe?" → CAPABILITIES.md ## Capabilities and modes
  • TASKS.md ## modify.
• "Will this pipe spec program the HW, or will commit fail?" → CAPABILITIES.md ## Safety policy
  • TASKS.md ## test.
• "How do I read Flow counters to investigate observed traffic?" → CAPABILITIES.md ## Observability
  • TASKS.md ## debug.
• "My Flow port won't start — Failed to get hws cap / dest action ROOT … err -121." → device-placement signature (not a pipe bug); the steering plane belongs to the DPU Arm on a SEPARATED_HOST / NIC-mode BlueField. See the device-placement bullet in CAPABILITIES.md ## Capabilities and modes
  • TASKS.md ## configure step 2 + Step 0 of TASKS.md ## debug.
• "How do I add hardware-accelerated stateful 5-tuple connection tracking (aging, NAT) on top of my existing doca-flow setup?" → CAPABILITIES.md ## flow-ct + TASKS.md ## flow-ct.

Audience

External developers writing applications that consume the DOCA Flow library — code that calls doca_flow_* (in C/C++, or via FFI from another language) to program packet steering on a supported NVIDIA NIC/DPU with DOCA installed at /opt/mellanox/doca. Flow ships as a C library (pkg-config module doca-flow, package doca-sdk-flow on Ubuntu / RHEL / SLES) and the samples are C, so C/C++ is the canonical path the TASKS.md examples assume; other-language consumers reach the same *.so through FFI, and the skill keeps its API-surface, lifecycle, capability-discovery, error-taxonomy, and safety guidance language-neutral.

When to load this skill

Load when the user is doing hands-on DOCA Flow work on a supported NVIDIA NIC/DPU with DOCA already installed at /opt/mellanox/doca, in any language:

• Bringing up a Flow port / representor on the installed devices.
• Creating pipes, defining match/actions, programming entries.
• Validating a pipe spec before programming the hardware.
• Reading per-entry / per-pipe counters under traffic.
• Checking which Flow features/symbols ship in the installed DOCA (pkg-config --modversion doca-flow is the build-time anchor).
• Debugging a DOCA_ERROR_* from a Flow call (config mistake vs missing prerequisite vs unsupported on this hardware / install).
• Designing non-C bindings (Rust, Go, Python, …) over the Flow C ABI.
• Adding stateful CT (doca_flow_ct.h) on top of an existing port (see TASKS.md ## flow-ct).

Do not load for general DOCA orientation, "where do I find docs", install-layout, or non-Flow library questions — use doca-public-knowledge-map.

What this skill provides

This is a thin loader; substantive material lives in two companion files:

• CAPABILITIES.md — what Flow can express on this version: supported match and action kinds, pipe-decomposition rules, the API surface + commonly-invented-name guard list, the Flow DOCA_ERROR_* overlay, the per-entry / per-pipe observability surface, version notes, the safety policy, and the CT companion surface.
• TASKS.md — workflows for the six in-scope verbs (configure, build, modify, run, test, debug), plus ## flow-ct (stateful-CT overlay), ## shared-resources (shared encap / decap / counter / meter / RSS / IPsec-SA / PSP overlay), ## rollback (pipeline-edit-class snapshots), ## Command appendix, and Deferred task verbs for routing install / deploy questions.

The skill assumes DOCA is installed at /opt/mellanox/doca and the user can open a doca_dev. Installing DOCA, hugepages setup, and the EAL dv_flow_en devargs prep go through doca-setup; the hugepages / devargs runtime prerequisites a binary needs before a Flow port starts are pinned in TASKS.md ## configure step 5.

What this skill deliberately does not ship

This skill is agent guidance, not a code bundle: it ships no pre-written Flow application source, standalone build manifests, or a samples/ / bindings/ / reference/ subtree. The verified Flow source is the shipped C sample at /opt/mellanox/doca/samples/doca_flow/<name>/ — the agent routes the user there and prescribes a minimum-diff edit via the modify-a-sample workflow in doca-programming-guide plus the Flow overrides in TASKS.md ## build, and builds any manifest in the user's project against the user's install, where pkg-config --modversion doca-flow is the source of truth.

Loading order

1. Read this SKILL.md first to confirm the question is in scope.
2. For the pipe-spec schema, capability matrix, error taxonomy, observability, and safety policy, see CAPABILITIES.md.
3. For step-by-step workflows, see TASKS.md.

Related skills

• doca-public-knowledge-map — routing table for public DOCA docs and the on-disk layout of an installed package.
• doca-setup — env prep, install verification, and the no install yet path via the NGC DOCA container.
• doca-programming-guide — general DOCA patterns shared by every library: the pkg-config + meson build pattern, the modify-a-shipped-sample first-app workflow, the universal lifecycle, the cross-library DOCA_ERROR_* taxonomy, and the program-side debug order. This skill layers Flow specifics on top.
• doca-flow-tune — programmed-state inspection (read-only).
• doca-hardware-safety — required overlay for card-mode flips (e.g. mlxconfig change from SEPARATED_HOST to EMBEDDED_CPU).
• doca-debug — the cross-cutting debug ladder (install / version / build / link / runtime / program / driver).