[PATCH v6 00/11] net/rtap: add io_uring based TAP driver

[Stephen Hemminger <stephen@networkplumber.org>]

This series adds net_rtap, an experimental poll mode driver that uses
Linux io_uring for asynchronous packet I/O with kernel TAP interfaces.

Like net_tap, net_rtap creates a kernel network interface visible to
standard tools (ip, ethtool) and the Linux TCP/IP stack.  From DPDK
it is an ordinary ethdev.

Motivation
----------

This driver started as an experiment to determine whether Linux
io_uring could deliver better packet I/O performance than the
traditional read()/write() system calls used by net_tap.  By posting
batches of I/O requests asynchronously, io_uring amortizes system
call overhead across multiple packets.

The project also served as a testbed for using AI tooling to help
build a comprehensive test suite, refactor code, and improve
documentation.  The result is intended as an example for other PMD
authors: the driver has thorough unit tests covering data path,
offloads, multi-queue, fd lifecycle, and more, along with detailed
code comments explaining design choices.

Why not extend net_tap?
-----------------------

The existing net_tap driver was designed to provide feature parity
with mlx5 when used behind the failsafe PMD.  That goal led to
significant complexity: rte_flow support emulated via eBPF programs,
software GSO implementation, and other features that duplicate in
user space what the kernel already does.

net_rtap takes the opposite approach -- use the kernel efficiently
and let it do what it does well.  There is no rte_flow support;
receive queue selection is left to the kernel's native RSS/steering.
There is no software GSO; the driver passes segmentation requests
to the kernel via the virtio-net header and lets the kernel handle
it.  The result is a much simpler driver that is easier to maintain
and reason about.

Given these fundamentally different design goals, a clean
implementation was more practical than refactoring net_tap.

Acknowledgement
---------------

Parts of the test suite, code review, and refactoring were done
with the assistance of Anthropic Claude (AI).  All generated code
was reviewed and tested by the author.

Requirements:
  - Kernel headers with IORING_ASYNC_CANCEL_ALL (upstream since 5.19)
  - liburing >= 2.0

Should work on distributions: Debian 12+, Ubuntu 24.04+,
Fedora 37+, SLES 15 SP6+ / openSUSE Tumbleweed.
RHEL 9 is not supported (io_uring is disabled by default).

v6:
  - fix lots of bugs found doing automated review
  - convert to use ifindex and netlink to avoid rename issues
  - implement xstats

Stephen Hemminger (11):
  net/rtap: add driver skeleton and documentation
  net/rtap: add TAP device creation and queue management
  net/rtap: add Rx/Tx with scatter/gather support
  net/rtap: add statistics and device info
  net/rtap: add link and device management operations
  net/rtap: add checksum and TSO offload support
  net/rtap: add multi-process support
  net/rtap: add link state change interrupt
  net/rtap: add Rx interrupt support
  net/rtap: add extended statistics support
  test: add unit tests for rtap PMD

 MAINTAINERS                            |    7 +
 app/test/meson.build                   |    1 +
 app/test/test_pmd_rtap.c               | 2620 ++++++++++++++++++++++++
 doc/guides/nics/features/rtap.ini      |   26 +
 doc/guides/nics/index.rst              |    1 +
 doc/guides/nics/rtap.rst               |  101 +
 doc/guides/rel_notes/release_26_03.rst |    7 +
 drivers/net/meson.build                |    1 +
 drivers/net/rtap/meson.build           |   30 +
 drivers/net/rtap/rtap.h                |  152 ++
 drivers/net/rtap/rtap_ethdev.c         |  864 ++++++++
 drivers/net/rtap/rtap_intr.c           |  207 ++
 drivers/net/rtap/rtap_netlink.c        |  445 ++++
 drivers/net/rtap/rtap_rxtx.c           |  803 ++++++++
 drivers/net/rtap/rtap_xstats.c         |  293 +++
 15 files changed, 5558 insertions(+)
 create mode 100644 app/test/test_pmd_rtap.c
 create mode 100644 doc/guides/nics/features/rtap.ini
 create mode 100644 doc/guides/nics/rtap.rst
 create mode 100644 drivers/net/rtap/meson.build
 create mode 100644 drivers/net/rtap/rtap.h
 create mode 100644 drivers/net/rtap/rtap_ethdev.c
 create mode 100644 drivers/net/rtap/rtap_intr.c
 create mode 100644 drivers/net/rtap/rtap_netlink.c
 create mode 100644 drivers/net/rtap/rtap_rxtx.c
 create mode 100644 drivers/net/rtap/rtap_xstats.c

-- 
2.51.0