[RFC 0/4] alternative capture mechanism

[Bruce Richardson]

On Tue, Jun 09, 2026 at 02:02:01PM -0700, Stephen Hemminger wrote:
> This is an RFC for an alternative way to capture packets from a DPDK
> application. I did brief demo of similar mechanism at DPDK summit but
> this is more complete. Capture runs in the primary process and is driven
> entirely over telemetry; no secondary process is involved.
> 
> A client asks the application to start capturing and passes it a file
> descriptor to write to. The application writes pcapng to that descriptor.
> A Wireshark extcap script is the intended front end, but the control path
> is just telemetry and the output is just a pipe, so other front ends are
> possible.
> 
>   1/4  telemetry: let a command receive file descriptors from the client
>   2/4  capture: the library
>   3/4  test: functional test
>   4/4  app: the Wireshark extcap script and its documentation
> 
> Setup and usage are in doc/guides/tools/wireshark_extcap.rst.
> 
> Primary process only for now; secondary-process capture is possible as
> follow-on. Posting as RFC to get feedback on the approach.
> 
> The extcap script is dual licensed (BSD-3-Clause OR GPL-2.0-or-later) as
> it may be more useful in the Wireshark tree.
> 

One concern I have though - does this cause system-calls to be made in the
fast-path because we are writting to a passed in FD? For performance
reasons, would it not be better to use a memory buffer for this, thereby
avoiding syscalls? For example, rather than passing in an FD to telemetry,
we could pass in a key to be passed to shmget (going old-school!), or
name parameter for shm_open. Thereafter with the memory buffer we can use a
circular ring or similar to pass the data from app to client.

/Bruce

> Stephen Hemminger (4):
>   telemetry: allow commands to receive file descriptors
>   capture: infrastructure wireshark packet capture
>   test: add test for capture hooks
>   usertools/dpdk-wireshark-extcap.py: script for external capture
> 
>  MAINTAINERS                            |   4 +
>  app/test/meson.build                   |   1 +
>  app/test/test_capture.c                | 365 +++++++++++
>  doc/guides/rel_notes/release_26_07.rst |  12 +
>  doc/guides/tools/index.rst             |   1 +
>  doc/guides/tools/wireshark_extcap.rst  | 155 +++++
>  lib/capture/capture.c                  | 821 +++++++++++++++++++++++++
>  lib/capture/capture_impl.h             |  56 ++
>  lib/capture/filter.c                   | 108 ++++
>  lib/capture/meson.build                |  19 +
>  lib/meson.build                        |   1 +
>  lib/telemetry/rte_telemetry.h          |  66 ++
>  lib/telemetry/telemetry.c              | 115 +++-
>  usertools/dpdk-wireshark-extcap.py     | 274 +++++++++
>  14 files changed, 1986 insertions(+), 12 deletions(-)
>  create mode 100644 app/test/test_capture.c
>  create mode 100644 doc/guides/tools/wireshark_extcap.rst
>  create mode 100644 lib/capture/capture.c
>  create mode 100644 lib/capture/capture_impl.h
>  create mode 100644 lib/capture/filter.c
>  create mode 100644 lib/capture/meson.build
>  create mode 100755 usertools/dpdk-wireshark-extcap.py
> 
> -- 
> 2.53.0
>