Re: [RFC 1/3] flow_compile: introduce textual flow rule compiler

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, May 05, 2026 at 08:29:55PM -0700, Stephen Hemminger wrote:
> Currently the only way to compile a flow rule from text is to link
> against testpmd's cmdline_flow.c, which is tightly coupled to
> librte_cmdline and the testpmd command framework.  Recent attempts
> to extract it as a library have produced ad-hoc copies rather than
> a clean separation.
> 
> Add librte_flow_compile, modelled on libpcap's pcap_compile(): a
> textual rule goes in, an opaque compiled object comes out, and
> diagnostics of the form "line:col: message" go in a caller-supplied
> buffer.  Accessors return the rte_flow_attr/item/action arrays
> ready for rte_flow_create(); a convenience entry point installs
> the rule directly on a port.
> 
> The parser is recursive descent driven by descriptor tables of
> items and actions, so adding a new item type is purely a table
> edit -- the parser has no per-type knowledge.  A custom-setter
> hook handles fields whose layout cannot be expressed as a plain
> byte range (bitfields, indirect arrays).
> 
> Dependencies are limited to rte_ethdev and rte_net; no
> librte_cmdline, no flex/bison, no platform-specific headers.
> The grammar follows testpmd's syntax so familiar rules carry
> over and is documented in the programmer's guide.
> 
Was there a particular reason to avoid using flex/bison here, or did their
use just not make sense? In general I would prefer using code-generation
tools where possible rather than maintaining (metaphorically) hand-written code.

/Bruce