rte_flow: no ability to match on packet length?

[Stephen Hemminger]

On Tue, 28 Feb 2023 15:12:31 +0000
Tony Hart <Tony.Hart at corero.com> wrote:

> I’m trying to use the Generic Flow API (rte_flow) to match IP packets based on their length (either L2, L3 or L4 lengths).
>  
> There doesn’t seem to be an item type that explicitly matches based on length (RTE_FLOW_ITEM_TYPE_x).  So I’ve tried using a mask with RTE_FLOW_ITEM_TYPE_IPV4 to match on the total_length field (and similar attempt to match on the UDP header dgram_len field) but the NIC I’m using (mlx5) returns an error (mask enables non supported bits).
>  
> Am I out of luck, or maybe missing something?
>  
> Thanks for any insights!
>  
> I’ve tried, DPDK: 20.11.7 and 22.11.1
> 
> Tony Hart | Chief Architect
> Tony.Hart at corero.com <mailto:Tony.Hart at corero.com> 

Short answer: yes, you are right there is no generic length match.

Longer answer: rte_flow is an API which is meant to provide access to the underlying
match features of NIC hardware. Supporting something requires that the HW/FW can do the
match, and that the driver writer has added (and tested) that match.

Hopefully the MLX5 experts can help answer what is possible.