RFCv1: DPDK RTE Flow Rule Parser

["Lukáš Šišmiš" <sismis@cesnet.cz>]

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Hello all,

## Motivation

Recent discussions on DPDK Slack raised the idea of extracting the 
rte_flow rule parser currently embedded in dpdk-testpmd into a 
standalone, reusable library [1].

The main motivation is that the external applications, such as Suricata 
IDS [2], often need to express hardware filtering rules in a consistent 
and human-readable format.

When integrating rte_flow into Suricata [3], we encountered the lack of 
a unified way to define such rules. The immediate need was to let users 
specify input filters (drop/allow) determining which traffic should be 
inspected.

Suricata’s existing capture modes (e.g. AF-PACKET) rely on BPF filters 
[4]. Maintaining consistency across Suricata capture backends would be 
ideal, but BPF and rte_flow differ significantly in expressiveness.

The other options include either dpdk-testpmd or custom rule syntax. To 
not reinvent the wheel, I am leaning towards use of the testpmd syntax 
for the ready-to-use generic expressibility, especiaily of the network 
traffic patterns. For the reference, I am speaking of the rte_flow rule 
syntax that you can define through testpmd CLI, e.g., "flow create 0 
ingress pattern eth / vlan vid is 0xabc / ipv4 src is 192.168.0.1 src is 
53 / tcp / end actions drop / end".

In the Slack, Thomas Monjalon concluded that it is generally welcome to 
see a new parser library but we need to state it is just one way how 
create rte_flow C structures. (Fine by me)

## Library proposal

The existing function flow_parse() in dpdk-testpmd already performs most 
of the needed work:

int
flow_parse(const char *src, void *result, unsigned int size,
       struct rte_flow_attr **attr,
       struct rte_flow_item **pattern, struct rte_flow_action **actions)

It parses a rule expressed in testpmd syntax and initializes rte_flow 
attributes, items, and actions.
External applications that use these structures directly can skip 
redundant setup logic and rely on standard DPDK APIs (validate, create, 
destroy).

For a public API, the void *result and unsigned int size parameters 
appear unnecessary and could be removed. The simplified interface would 
only expose the meaningful outputs (attr, pattern, actions).

## Problem statement

The main question is how to provide this parser without fragmenting 
existing functionality.

I would like to extract the existing code from dpdk-testpmd to have one 
parser that is available and used by both testpmd and external apps 
(using the library itself).
I quickly run into the complexity of the testpmd code and how entangled 
the C structures are throughout the testpmd's source code.
While the parser extraction should be possible, I wanted to check here 
with the community if that is the most preferred approach.
Since the extraction moves a lot of code from place to another, there is 
a very good chance that it would break all forked custom testpmds.

The other alternative is to "start simple" with an alternative 
implementation, perhaps only focusing on subset of testpmd's parser 
capabilities. But this would very likely lead to two places being 
maintained independently.

Before taking either route, I’d like to understand the community’s 
preference:
- Do you even see it as a valuable contribution for customer applications?
- Can you possibly think of an alternative way to solve the unified 
human-readable format conversion? Both on the code level and interface 
level.
- Is testpmd code extraction the right long-term solution, even if 
disruptive? Should the private DPDK forks be taken into consideration? 
Or should I start with a separate lightweight parser and revisit 
integration later?

Any other feedback is welcome.


Thank you.

All the best,
Lukas


[1] https://dpdkproject.slack.com/archives/CB2UPBU48/p1759765888891329
[2] https://github.com/OISF/suricata
[3] https://github.com/OISF/suricata/pull/13950
[4] https://docs.suricata.io/en/latest/performance/ignoring-traffic.html



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