Doca Devemu

---
license: Apache-2.0
name: doca-devemu
description: >
  Use this skill when the user is doing hands-on DOCA Device
  Emulation on a BlueField DPU — exposing a custom emulated PCIe
  device the host sees as a real peripheral while DPU-side code
  runs the backend, picking the sub-library (PCI Generic,
  virtio-net, virtio-fs), wiring the per-sub-library Core context
  plus doorbell / DMA primitives, querying `doca_devemu_*_cap_*`,
  or debugging DOCA_ERROR_* from a `doca_devemu_*` call. Trigger
  even when the user does not say "devemu" — typical implicit
  phrasings include "expose a custom PCIe device from BlueField to
  the host", "host should see a virtio NIC backed by my DPU code",
  "lspci does not show my emulated device", "device enumerated but
  no driver binds", "DPU sees nothing when host kicks the queue",
  or "virtio feature negotiation failed at bind". Refuse and route
  elsewhere for the packaged DOCA SNAP / Virtio-net Services,
  host-side virtio kernel drivers, backend body design, or standard
  BlueField NIC behavior — those belong to other skills.
metadata:
  kind: library
compatibility: >
  Requires DOCA SDK installed at /opt/mellanox/doca on BOTH the
  host AND the BlueField DPU (Ubuntu 22.04/24.04 or RHEL/SLES),
  with the per-sub-library firmware-level emulation type (PCI
  Generic / virtio-net / virtio-fs) enabled in BlueField firmware
  and the host kernel shipping the matching standard driver
  (virtio_net / virtio_fs / generic PCIe). Reads the local install
  via the per-sub-library pkg-config module and inspects
  /opt/mellanox/doca/{lib,include,samples/doca_devemu}.
---

# DOCA Device Emulation

**Where to start:** This skill assumes DOCA is already installed
on the host AND on the BlueField, the user is doing **hands-on
emulated-PCIe-device work** from the DPU side (writing the
backend that the host's kernel driver will talk to over the
emulated PCIe surface), and the user knows which CLASS of
emulated device they want to build. 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 Device Emulation express* on this DOCA version + this
BlueField generation + this firmware. If the user has not
installed DOCA yet, route to
[`doca-setup`](../../doca-setup/SKILL.md) first. **Before
anything else, the agent must route the user to the right
sub-library** — DOCA Device Emulation is an *umbrella* that
covers PCI Generic (raw PCIe device emulation), virtio-net
(emulated virtio network device), and virtio-fs (emulated
virtio filesystem device); each sub-library has its own
context, its own `pkg-config` module, and its own capability
surface. The sub-library selection rule lives in
[`CAPABILITIES.md ## Capabilities and modes`](CAPABILITIES.md#capabilities-and-modes).
If the user wants a packaged solution rather than a library
(e.g. *"I want NVMe SNAP on my host without writing the
backend myself"*, or *"I want a managed virtio-net daemon"*),
route via
[`doca-public-knowledge-map`](../../doca-public-knowledge-map/SKILL.md)
to the DOCA SNAP Service / DOCA Virtio-net Service guides
— those services are *built on top of* this library and are a
different artifact than what this skill covers.

## Audience

This skill serves **external developers building applications
that consume the DOCA Device Emulation library** — i.e., users
whose DPU-side code calls `doca_devemu_pci_*`,
`doca_devemu_virtio_*`, or `doca_devemu_vfs_*` (directly
in C / C++, or through FFI / bindings from another language)
to expose an emulated PCIe device to the host that the host's
existing kernel drivers can drive as if it were a real PCIe
peripheral. It is *not* for NVIDIA developers contributing to
DOCA Device Emulation itself, and it is *not* the right
artifact for users who want a packaged emulated-device daemon
they do not have to write the backend for (the DOCA SNAP
Service and the DOCA Virtio-net Service are the packaged
options that build on top of this library).

**Language scope.** DOCA Device Emulation ships as a C library;
this skill covers three sub-libraries end-to-end. Select the exact
installed `pkg-config` module for the user's emulation class (see
the sub-library selection table in
[`CAPABILITIES.md ## Capabilities and modes`](CAPABILITIES.md#capabilities-and-modes)).
The shipped samples under
`/opt/mellanox/doca/samples/doca_devemu/` are
written in C. C and C++ consumers are the canonical case and
the worked examples in `TASKS.md` assume that path.
Other-language consumers (Rust, Go, Python, …) consume the
same `*.so` files through FFI or language-specific bindings;
the skill's contribution in that case is to keep the
sub-library selection, umbrella 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 Device
Emulation work from the DPU side, in any language. Concretely:

- Deciding which Device Emulation sub-library (PCI Generic,
  virtio-net, virtio-fs) the user needs — the umbrella
  selection question is *this skill's load-bearing first move*.
- Initializing the per-sub-library DOCA Core context on the
  DPU (one context per emulated device per sub-library) and
  configuring the doorbell / DMA primitives the host's PCIe
  driver will interact with.
- Reading per-sub-library capability surface via the
  `doca_devemu_pci_cap_*`, `doca_devemu_virtio_cap_*`, or
  `doca_devemu_vfs_cap_*` query families against the
  active `doca_devinfo` BEFORE assuming a particular feature
  bit or device characteristic is available.
- Choosing between writing the backend with `doca-devemu`
  yourself and adopting a packaged service (DOCA SNAP Service
  / DOCA Virtio-net Service) that already wraps this library.
- Debugging a `DOCA_ERROR_*` returned from a `doca_devemu_*`
  call — in particular disambiguating *firmware-level
  emulation type not enabled* from *BlueField generation does
  not support this sub-library at all* from *DPU-side process
  lacks privilege* from *host-side kernel driver did not bind*.
- Designing or extending non-C bindings (Rust, Go, Python, …)
  that wrap one of the device-emulation sub-libraries — for
  the sub-library selection, umbrella lifecycle, capability-
  discovery, permission, and error-taxonomy rules the wrapper
  must honor.

Do **not** load this skill for general DOCA orientation,
install of DOCA itself, the host-side kernel driver for the
emulated device class (virtio-net / virtio-blk / virtio-fs
kernel drivers ship with the host kernel and are not part of
DOCA), the packaged SNAP / Virtio-net services (they are
separate artifacts with their own service guides), or for
standard NIC behavior on the BlueField data path (use
[`doca-flow`](../doca-flow/SKILL.md) +
[`doca-eth`](../doca-eth/SKILL.md) instead — Device Emulation
is for *custom* emulated devices, not for shaping the
BlueField's built-in NIC personality).

## What this skill provides

This is a **thin loader**. The body keeps only the orientation
needed to pick the right next file. The substantive Device
Emulation-specific material lives in two companion files:

- `CAPABILITIES.md` — what Device Emulation can express on
  this version + this BlueField generation + this firmware:
  the umbrella architecture (host sees an emulated PCIe
  device; DPU runs the backend), the sub-library selection
  rule (PCI Generic vs virtio-net vs virtio-fs), the per-
  sub-library Core context shape, the doorbell / DMA
  primitives that bridge host ↔ DPU, the per-sub-library
  capability-query family (`doca_devemu_*_cap_*`), the
  per-sub-library `pkg-config` module name, the Device
  Emulation error taxonomy mapped onto the cross-library
  `DOCA_ERROR_*` set, the observability surface, the
  library-vs-packaged-service path-selection rule, and the
  safety policy that gates env preconditions (DPU-side
  privileges, BlueField firmware-level emulation type
  enablement, BlueField generation actually supporting the
  emulation class).
- `TASKS.md` — step-by-step workflows for the six in-scope
  Device Emulation verbs: `configure`, `build`, `modify`,
  `run`, `test`, `debug`. Plus a `Deferred task verbs` block
  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 on both sides, the
BlueField firmware has the emulation type the user wants to
build enabled, the user has the privileges their public
install profile expects (in particular, sudo on the DPU side
to perform PCIe-level emulation), and the host kernel ships
the standard driver for the emulated device class the user is
building. It does not cover installing DOCA, flipping
firmware-level configuration, or installing host-side kernel
drivers — those paths go through
[`doca-setup`](../../doca-setup/SKILL.md).

## Loading order

1. Read this `SKILL.md` first to confirm the user's question
   is in scope (custom emulated PCIe device built on the
   `doca-devemu` library, not the packaged SNAP /
   Virtio-net services, not the host-side kernel driver, not
   standard NIC behavior).
2. **For the umbrella architecture, the sub-library selection
   rule (PCI Generic vs virtio-net vs virtio-fs), the per-
   sub-library Core context shape, the doorbell / DMA
   primitives, the per-sub-library capability-query rule,
   the per-sub-library `pkg-config` modules, the library-vs-
   packaged-service path-selection rule, the error taxonomy,
   the observability surface, and the safety policy, see
   [CAPABILITIES.md](CAPABILITIES.md).**
3. **For step-by-step workflows — configure, build, modify,
   run, test, debug — see [TASKS.md](TASKS.md).**

Both companion files cross-link to each other,
[`doca-version`](../../doca-version/SKILL.md) for the
canonical DOCA version-handling rules (with the Device
Emulation overlay that the chosen sub-library's `pkg-config`
module plus the firmware-level emulation slot plus the
`doca_devemu_*_cap_*` query are all part of *"is this
emulation supported here"*), and
[`doca-public-knowledge-map`](../../doca-public-knowledge-map/SKILL.md)
whenever the right answer is "look it up in the public DOCA
Device Emulation umbrella guide, the per-sub-library guide
linked from it, the DOCA SNAP / Virtio-net Service guide, or
in the on-disk install layout" rather than "Device Emulation-
specific guidance".

## Example questions this skill answers well

See [`references/details.md`](references/details.md#example-questions-this-skill-answers-well).
## What this skill deliberately does not ship

See [`references/details.md`](references/details.md#what-this-skill-deliberately-does-not-ship).
## Related skills

See [`references/details.md`](references/details.md#related-skills).