Hi Pablo, Harald,
The in-tree GTP driver supports GTPv0 and GTPv1-U, but has no handling for the 5G N3 PDU Session Container (PSC) extension header (type 0x85, 3GPP TS 29.281 / TS 38.415) that carries the QoS Flow Identifier (QFI). drivers/net/gtp.c also still has the "TODO: Support for extension header, sequence number and N-PDU" on the xmit path.
I'd like to add PSC/QFI support, but before writing the datapath code I wanted to check two things with you.
1) Is this something you'd welcome in mainline gtp.c? I'm aware a lot of 5G user-plane work lives in out-of-tree datapaths (gtp5g, the eBPF eUPF), so I don't want to add datapath complexity you'd rather not carry here.
2) If yes: on RX, once the QFI has been parsed out of the PSC, what would you like the driver to do with it? The options I see are: - stash it in skb->mark, so tc/nftables can classify uplink traffic by QoS flow; - attach it as skb metadata (tc_skb_ext / metadata_dst); or - just validate it and otherwise ignore it. The shape of the RX patch depends on this, so I'd rather ask than guess.
The plan would be a small incremental series: 1. add a GTPA_QFI (u8) netlink attribute + ynl spec, stored per PDP context (control-plane plumbing only); 2. RX: parse the PSC extension header and extract the QFI; 3. TX: build the PSC from the per-PDP QFI on the downlink path (the existing extension-header TODO).
Patch 1 is already written and builds; I'll post the series once I know whether you want it in mainline and how you'd prefer the RX QFI to be surfaced. Happy to adjust the approach.
Thanks, Anil