Doca Comch
NVIDIAOfficialCreated by NVIDIA
- Skill
- Tool integration
- Software development
- Apache-2.0
- Medium risk
AutoGineer summary
Written by AutoGineer from the skill’s own files, not by the author
This skill provides specialized support for developers building applications that utilize the DOCA Comch library to exchange control or data messages between a host and a BlueField DPU over PCIe. It covers the full lifecycle of Comch development, including role selection (server vs. client), path optimization (slow-path vs. fast-path), connection management, and debugging API errors. The skill is designed to integrate with existing DOCA installations and provides structured workflows for configuring, building, and troubleshooting Comch-based communication channels.
What it does
- Guides the initialization of Comch servers on DPUs and clients on hosts.
- Assists in choosing between slow-path (task/callback) and fast-path (producer/consumer) communication modes.
- Provides workflows for configuring connection callbacks and managing state transitions.
- Helps debug DOCA_ERROR_* codes specific to the Comch API.
- Explains how to query and set library capabilities like message sizes and client limits.
- Maps Comch-specific terminology and versioning changes, such as the 2.5 rename from Comm Channel.
When to use it
- When implementing PCIe control-plane messaging between a host and a BlueField DPU.
- When debugging connection failures or representor visibility issues.
- When optimizing data streaming performance using producer/consumer fast-paths.
- When needing to understand the Comch error taxonomy and lifecycle requirements.
- When developing language bindings that wrap the Comch C ABI.
Advantages
- Provides clear, structured workflows for complex DPU-host communication tasks.
- Offers specific guidance on performance optimization through path selection.
- Ensures consistent handling of DOCA versioning and library-specific error codes.
- Integrates seamlessly with standard DOCA development environments and tools.
- Reduces development friction by providing clear paths for common configuration and debugging scenarios.
Usage examples
- “Send a control message from host to BlueField over PCIe.”
- The agent will guide you through selecting the appropriate server/client roles and implementing the necessary send/recv logic using the Comch API.
- “Why is doca_comch_server_create returning DOCA_ERROR_NOT_PERMITTED?”
- The agent will help you verify representor visibility and DPU-side permissions, routing to setup documentation if environment issues are detected.
- “How do I stream bulk data from a host driver to a DPU agent with low CPU?”
- The agent will direct you to the fast-path producer/consumer implementation workflow to ensure efficient data transfer.
- “Is doca_comch_producer available in my DOCA version?”
- The agent will check your installed version and confirm availability, providing guidance on whether to use the new API or the legacy slow-path.
Install
Download the skill as a ZIP:
https://mp-staging.autogineer.com/agent-skills/nvidia/doca-comch/downloadUnzip it into the cross-client skills folder of your project:
mkdir -p .agents/skills && unzip doca-comch.zip -d .agents/skills
Documentation by NVIDIA
DOCA Comch
Examples
"Send a control message from host to BlueField over PCIe." — this is in scope. Pick server (DPU) vs client (host) and stay on the Comch send/recv path; do not fall back to TCP.
"Connect callback never fires." — check role, representor visibility, and the 2.5 rename overlay before rewriting the app as raw verbs.
Instructions
Follow Loading order below. Open the tasks companion for configure / modify / debug. Open the capabilities companion for slow-path vs fast-path and the 2.5 rename. Do not open every companion file.
Where to start: This skill assumes DOCA is already installed and
the user is doing hands-on Comch work on a BlueField + host
pair with DOCA. Open the tasks companion if the user wants to
do something (configure / build / modify / run / test / debug);
open the capabilities companion when the question is
what can Comch express on this version. If the user has not
installed DOCA yet, route to
doca-setup/SKILL.md first. If the user is
asking "is Comch even on this DOCA" because the docs they read
mention doca-comm-channel, route to
Version compatibility
for the 2.5 rename.
Example questions this skill answers well
The CLASSES of Comch 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 a Comch channel between host and DPU?" — worked example: "server side on the DPU, client side on the host, exchange a first control message". Answered by the role-selection + lifecycle workflow in
configure +
Capabilities and modes
server-vs-client table.
"How do I move bulk data over Comch with low CPU?" — worked example: "stream a 64 KiB chunk every 100 µs from the host driver to a DPU agent". Answered by the producer / consumer fast-path described in
Capabilities and modes
the channel-setup workflow in
configure
step 4, with the "slow-path vs fast-path" selection rule.
"What is the maximum message size I can send?" — worked example: "can I send a 4 MiB control message in one shot?". Answered by the capability-query rule (
doca_comch_cap_get_max_msg_size) inCapabilities and modes
the property-set workflow in
modify.
"Why doesn't the DPU side see the representor?" — worked example: "
doca_comch_server_createreturnsDOCA_ERROR_NOT_PERMITTEDon a freshly imaged BlueField". Answered by the representor + permission overlay inSafety policy
the env-prep checklist in
configure step 1, which
routes representor-side env questions to
doca-setup/SKILL.md."Is this Comch capability on my installed DOCA version?" — worked example: "is
doca_comch_producerin DOCA 2.6.0, or do I still need the old slow-path API?". Answered by the version-compatibility overlay inVersion compatibility,
which cross-links the canonical detection chain in
doca-version/SKILL.mdand adds the Comch-specific 2.5 rename rule."What does this
DOCA_ERROR_*from a Comch call mean and which layer caused it?" — worked example: "DOCA_ERROR_AGAINon submitting adoca_comch_task_sendviadoca_task_submit". Answered by the Comch overlay on the cross-library taxonomy inError taxonomy
the layered ladder in
debug that escalates to
doca-debug/SKILL.md.
Audience
This skill serves external developers building applications that
consume the DOCA Comch library — i.e., users whose code calls
doca_comch_* (directly in C/C++, or through FFI/bindings from
another language) to exchange control or data messages between a
host process and a BlueField agent over PCIe. It is not for
NVIDIA developers contributing to DOCA Comch itself.
Language scope. DOCA Comch ships as a C library with
pkg-config module name doca-comch. The shipped samples are
written in C. C and C++ consumers are the canonical case; the
worked examples in the tasks companion 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 role-split, lifecycle,
capability-discovery, permission, 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 Comch work, in any language. Concretely:
Initializing a
doca_comch_serveron the DPU side or adoca_comch_clienton the host side, on a representor or PCIe address the host can reach.Configuring at least one of: a recv callback for slow-path messages, a producer for fast-path outbound data, a consumer for fast-path inbound data, before
doca_ctx_start().Reading or setting comch properties via
doca_comch_set_*anddoca_comch_cap_get_*— max message size, max number of clients (server side), producer / consumer queue sizing.Establishing a connection between the two sides and reacting to connection-state transitions via the connection callbacks registered before start.
Choosing between the slow-path (send-task / recv-callback, message-oriented, lower throughput, single-call simplicity) and the fast-path (producer / consumer, asynchronous, much higher throughput, two-context setup).
Debugging a
DOCA_ERROR_*returned from a Comch call (lifecycle vs. permission vs. capability vs. would-block) and the connection state machine across the host / DPU pair.Designing or extending non-C bindings (Rust, Go, Python, …) that wrap the Comch C ABI — for the lifecycle, role-split, permission, and capability rules the wrapper must honor.
Do not load this skill for general DOCA orientation, install
of DOCA itself, or non-Comch library questions. For those, use
doca-public-knowledge-map/SKILL.md.
What this skill provides
This is a thin loader. The body keeps only the orientation needed to pick the right next file. The substantive Comch-specific material lives in two companion files:
the capabilities companion — what Comch can express on this version: the server vs client role split, the slow-path send-task / recv-callback surface, the producer / consumer fast-path surface, the capability-query surface (
doca_comch_cap_get_*), the Comch error taxonomy (mapped onto the cross-libraryDOCA_ERROR_*set), the observability surface (connection state callbacks, task completion callbacks), and the safety policy that gates representor and permission decisions.the tasks companion — step-by-step workflows for the six in-scope Comch verbs:
configure,build,modify,run,test,debug. Plus aDeferred task verbsblock that points out-of-scope questions at the right next skill.
The skill assumes a host + BlueField pair where DOCA is already
installed at the standard location and the user has the privileges
their public install profile expects (in particular, sudo on the
DPU side to see the host representor). It does not cover installing
DOCA — that path goes through
doca-setup/SKILL.md.
What this skill deliberately does not ship
This skill is agent guidance, not a samples or templates bundle. To keep the boundary clean, it deliberately does not contain — and pull requests should not add:
Pre-written DOCA Comch application source code, in any language. The verified Comch source code is the shipped C samples at
/opt/mellanox/doca/samples/doca_comch/<name>/. The agent's job is to route the user to those files and prescribe a minimum-diff modification on them via the universal modify-a-sample workflow indoca-programming-guide/SKILL.md, layered with the Comch-specific overrides inmodify.
Standalone build manifests (
meson.build,CMakeLists.txt,Cargo.toml, …) parked inside the skill. The agent constructs the build manifest in the user's project directory against the user's installed DOCA, wherepkg-config --modversion doca-comchis the source of truth.A
samples/,bindings/, orreference/subtree of any kind. A mock or incomplete artifact in this skill's tree, even one labeled "reference", is misleading: users will read it as buildable.
Loading order
Read this skill first to confirm the user's question is in scope.
For the Comch capability matrix, role split, slow-path / fast-path surfaces, permission policy, error taxonomy, observability, and safety policy, see the capabilities companion.
For step-by-step workflows — configure, build, modify, run, test, debug — see the tasks companion.
Both companion files cross-link to each other,
doca-version/SKILL.md for the canonical
version-handling rules, and
doca-public-knowledge-map/SKILL.md
whenever the right answer is "look it up in the public docs or
the installed package layout" rather than "Comch-specific
guidance".
Related skills
doca-public-knowledge-map/SKILL.md— the routing table for every public DOCA documentation source and the on-disk layout of an installed DOCA package. The Comch URL slug isDOCA-Comch(DOCA 2.5+), notdoca-comm-channel.doca-setup/SKILL.md— env preparation, install verification, representor visibility checks, and the I have no install yet path with the public NGC DOCA container. This skill assumes its preconditions are satisfied.doca-version/SKILL.md— canonical DOCA version-handling rules. This skill's## Version compatibilitycross-links the four-way match rule and adds the Comch-specific 2.5 rename overlay.doca-structured-tools-contract/SKILL.md— the bundle's structured-tools precedence rule (detect / prefer / fall back / report). The Command appendix in the tasks companion honors this contract.doca-programming-guide/SKILL.md— general DOCA programming patterns shared by every library: the canonicalpkg-config+ meson build pattern, the universal modify-a-shipped-sample first-app workflow, the universal lifecycle, the cross-libraryDOCA_ERROR_*taxonomy, and the program-side debug order. This skill layers Comch specifics on top.doca-debug/SKILL.md— the cross-cutting debug ladder (install / version / build / link / runtime / program / driver). Comch-specific debug (lifecycle violations, representor visibility, slow-path vs fast-path queue-full symptoms) overlays on top of that ladder.
Files
- ATTRIBUTION.mdAdded by AutoGineer888 B
- BENCHMARK.md9.8 KiB
- CAPABILITIES.md16.1 KiB
- LICENSELicence file added by AutoGineer11.2 KiB
- SKILL.md12.1 KiB
- SKILLCARD.yaml2.7 KiB
- TASKS.md21.6 KiB
- evals/evals.json2.9 KiB
- skill-card.md4.7 KiB
- skill.oms.sig5.1 KiB
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Requirements and compatibility
Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta
“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.
The author says: Requires DOCA SDK installed at /opt/mellanox/doca on Linux (Ubuntu 22.04/24.04 or RHEL/SLES) on a host + BlueField pair (the Comch channel runs over the RoCE/IB protocol, not the TCP/IP stack). Reads the user's local install via `pkg-config doca-comch` (legacy `doca-comm-channel` on installs <2.5) and inspects /opt/mellanox/doca/{lib,include,samples,applications}. The validation steps require a live DOCA install.
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What our scanner noticed· Medium risk
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Attribution and licence
- Created by
- NVIDIA
- Publisher
- NVIDIA (Official)
- Source
- NVIDIA/skills · skills/doca-comch · commit fce3cca
- Licence
- Apache License 2.0 (redistribution allowed)
- LICENSE (added by AutoGineer from LICENSE-APACHE)
- ATTRIBUTION.md (written by AutoGineer)
- Synced
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The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download doca-comch.zip