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