[RFC v2 0/6] introduce PTP protocol library and software relay

[Rajesh Kumar]

This series introduces a new DPDK library (lib/ptp) for IEEE 1588-2019
PTP protocol packet processing and a companion example application
(ptp_tap_relay_sw) that demonstrates its usage.

Motivation
----------
Several DPDK applications need to classify and manipulate PTP packets
(e.g. ptpclient, ptp_tap_relay, custom Transparent Clocks). Today each
application re-implements its own PTP header parsing and correctionField
handling. A shared library avoids duplication and provides a tested,
standards-compliant foundation.

Library: lib/ptp
----------------
The library provides:
  - PTP header structures (IEEE 1588-2019 common header, timestamp,
    port identity)
  - Packet classification: rte_ptp_classify() detects PTP over L2
    (EtherType 0x88F7), VLAN-tagged L2 (TPIDs 0x8100/0x88A8, single
    or double), UDP/IPv4, UDP/IPv6 (ports 319/320), and VLAN-tagged
    UDP variants
  - Header access: rte_ptp_hdr_get() returns a pointer to the PTP
    header inside an mbuf
  - Inline helpers: correctionField manipulation (48.16 fixed-point),
    message type extraction, two-step flag check, timestamp conversion
  - Debug: rte_ptp_msg_type_str() for human-readable message names

The API is experimental (targeted for 26.07). Dependencies are minimal:
mbuf and net libraries only.

Example: ptp_tap_relay_sw
-------------------------
A minimal PTP Transparent Clock relay between a DPDK-bound physical NIC
and a kernel TAP interface using software timestamps only. No patched
kernel modules, custom TAP PMD, or hardware timestamp support is
required.

The relay:
  1. Receives packets on the physical NIC via DPDK
  2. Classifies PTP packets using rte_ptp_classify()
  3. For event messages, records software timestamps
     (CLOCK_MONOTONIC_RAW) at ingress and egress
  4. Adds residence time to correctionField via rte_ptp_add_correction()
     (IEEE 1588-2019 §10.2 Transparent Clock)
  5. Forwards bidirectionally: PHY <-> TAP

A two-pass design takes the TX timestamp as close to rte_eth_tx_burst()
as possible, minimising untracked delay.

Unit Tests: app/test
--------------------
A comprehensive test suite (ptp_autotest) covers all library APIs:
  - Packet classification across L2, VLAN, QinQ, IPv4-UDP, IPv6-UDP,
    and VLAN-tagged UDP encapsulations
  - Flag bit position validation (TWO_STEP, UNICAST, LI_61, LI_59)
  - correctionField manipulation and round-trip accuracy
  - Timestamp conversion, message type helpers, edge cases
  - Negative tests: truncated packets, bad IHL, non-PTP traffic
33 test cases total.

ptpclient Conversion
--------------------
The existing ptpclient example is converted to use lib/ptp shared
definitions (rte_ptp_hdr, rte_ptp_timestamp, rte_ptp_port_id,
RTE_PTP_ETHERTYPE, RTE_PTP_MULTICAST_MAC), removing ~120 lines of
duplicate struct and constant definitions.


Test Results
------------
Test setup: Intel E610 10GbE NIC (vfio-pci), ptp4l time transmitter
with HW timestamps on physical port, ptp4l time receiver with SW
timestamps (-S) on TAP interface, logSyncInterval=-4 (16 Sync/sec),
120s duration.

  Post-convergence (60s of locked data):
    Average RMS offset:   929 ns
    Worst max offset:     11615 ns (single transient)
    Steady-state range:   489 - 1055 ns RMS
    Corrections applied:  3635

linuxptp's PI servo uses relaxed gains for software timestamps
(kp=0.1, ki=0.001 vs kp=0.7, ki=0.3 for HW), expecting ~5-50 µs
jitter. Sub-microsecond RMS is achieved here because the time
transmitter uses HW timestamps and DPDK's poll-mode relay provides
deterministic low-latency forwarding.

v2:
    Fixed below AI generated Review comments 
  - Fixed flag bit positions for host-order representation after
    rte_be_to_cpu_16(): TWO_STEP (1<<9), UNICAST (1<<10),
    LI_61 (1<<0), LI_59 (1<<1).  Added unit test for all flags.
  - Fixed QinQ classification: outer 0x88A8 (802.1ad S-tag) now
    enters the VLAN parser alongside 0x8100.
  - Fixed signed left-shift UB in rte_ptp_add_correction(): shift
    is now performed on uint64_t before casting back to int64_t.
  - Fixed promiscuous enable failure in relay example: port_init()
    now returns error instead of logging and continuing silently.
  - Replaced deprecated master/slave PTP terminology with IEEE
    1588-2019 terms (time transmitter / time receiver) throughout
    code and documentation.
  - Documented per-burst single-timestamp design choice and its
    accuracy characteristics in the relay example.
  - Added IHL validation (reject IHL < 20) in IPv4 PTP-over-UDP path.
  - Changed rte_ptp_is_event() parameter from uint8_t to int with
    negative value guard for safe use with rte_ptp_classify() return.
  - Changed rte_ptp_hdr_get() parameter from const to non-const mbuf
    since it returns a non-const pointer into packet data.
  - All pointer accesses use rte_pktmbuf_mtod_offset() — no raw
    pointer arithmetic.
  - Added programmer's guide note about avoiding double-parse when
    both message type and header pointer are needed.

Rajesh Kumar (6):
  ptp: introduce PTP protocol library
  doc: add PTP library programmer's guide
  examples/ptp_tap_relay_sw: add software PTP relay example
  doc: add PTP software relay sample app guide
  app/test: add PTP library unit tests
  examples/ptpclient: use shared PTP library definitions

 MAINTAINERS                                   |    8 +
 app/test/meson.build                          |    1 +
 app/test/test_ptp.c                           | 1052 +++++++++++++++++
 doc/api/doxy-api-index.md                     |    1 +
 doc/api/doxy-api.conf.in                      |    1 +
 doc/guides/prog_guide/index.rst               |    1 +
 doc/guides/prog_guide/ptp_lib.rst             |  205 ++++
 doc/guides/rel_notes/release_26_07.rst        |   13 +
 doc/guides/sample_app_ug/index.rst            |    1 +
 doc/guides/sample_app_ug/ptp_tap_relay_sw.rst |  210 ++++
 examples/meson.build                          |    1 +
 examples/ptp_tap_relay_sw/Makefile            |   41 +
 examples/ptp_tap_relay_sw/meson.build         |   14 +
 examples/ptp_tap_relay_sw/ptp_tap_relay_sw.c  |  433 +++++++
 examples/ptpclient/meson.build                |    1 +
 examples/ptpclient/ptpclient.c                |  188 ++-
 lib/meson.build                               |    1 +
 lib/ptp/meson.build                           |    6 +
 lib/ptp/rte_ptp.c                             |  185 +++
 lib/ptp/rte_ptp.h                             |  338 ++++++
 20 files changed, 2585 insertions(+), 116 deletions(-)
 create mode 100644 app/test/test_ptp.c
 create mode 100644 doc/guides/prog_guide/ptp_lib.rst
 create mode 100644 doc/guides/sample_app_ug/ptp_tap_relay_sw.rst
 create mode 100644 examples/ptp_tap_relay_sw/Makefile
 create mode 100644 examples/ptp_tap_relay_sw/meson.build
 create mode 100644 examples/ptp_tap_relay_sw/ptp_tap_relay_sw.c
 create mode 100644 lib/ptp/meson.build
 create mode 100644 lib/ptp/rte_ptp.c
 create mode 100644 lib/ptp/rte_ptp.h

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2.53.0