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spliffedr | 1 month ago

Here are answers to both your questions:

The code has the infrastructure for XDP hardware offload:

- XDP_MODE_OFFLOAD enum exists in bpf_loader.h:61

- XDP_FLAGS_HW_MODE flag mapping in bpf_loader.c:789

But it's not usable in practice because:

1. No CLI option – There's no way to enable offload mode; it defaults to native with SKB fallback

2. BPF program isn't offload-compatible – The XDP program uses:

- Complex BPF maps (LRU hash, ring buffers)

- Helper functions not supported by most SmartNIC JITs

- The flow_cookie_map shared with sock_ops (can't be offloaded)

3. SmartNIC limitations

– Hardware offload typically only supports simple packet filtering/forwarding, not the stateful flow tracking spliff does

What would be needed for SmartNIC support:

- Split XDP program into offloadable (simple classification) and non-offloadable (stateful) parts

- Use SmartNIC-specific toolchains (Memory-1, Netronome SDK, etc.)

- Me having a device with SmartNIC and full driver support to play with. I've done all my testing on Fedora 43 on my device

For now this could be a future roadmap item, but the current "Golden Thread" correlation architecture fundamentally requires userspace + kernel cooperation that can't be fully offloaded.

Here is a sample debug output when you run spliff -d and it tries to detect all your NICs:

--- [DEBUG] Loaded BPF program from build-release/spliff.bpf.o [XDP] Found program: xdp_flow_tracker [XDP] Found required maps: flow_states, session_registry, xdp_events [XDP] Found optional map: cookie_to_ssl [XDP] Found map: flow_cookie_map (for cookie caching) [XDP] Found optional map: xdp_stats_map [XDP] Initialization complete [XDP] Discovered interface: enp0s20f0u2u4u2 (idx=2, mtu=1500, UP, physical) [XDP] Discovered interface: wlp0s20f3 (idx=4, mtu=1500, UP, physical) [XDP] Discovered interface: enp0s31f6 (idx=3, mtu=1500, UP, physical) libbpf: Kernel error message: Underlying driver does not support XDP in native mode [XDP] native mode failed on enp0s20f0u2u4u2, falling back to SKB mode [XDP] Attached to enp0s20f0u2u4u2 (idx=2) in skb mode libbpf: Kernel error message: Underlying driver does not support XDP in native mode [XDP] native mode failed on wlp0s20f3, falling back to SKB mode [XDP] Attached to wlp0s20f3 (idx=4) in skb mode libbpf: Kernel error message: Underlying driver does not support XDP in native mode [XDP] native mode failed on enp0s31f6, falling back to SKB mode [XDP] Attached to enp0s31f6 (idx=3) in skb mode [XDP] Attached to 3 of 3 discovered interfaces XDP attached to 3 interfaces [SOCKOPS] Using cgroup: /sys/fs/cgroup [SOCKOPS] Attached socket cookie caching program sock_ops attached for cookie caching [XDP] Warm-up: Seeded 5 existing TCP connections [DEBUG] Warmed up 5 existing connections ---

edit: formating is hard on my phone

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westurner|1 month ago

> Me having a device with SmartNIC and full driver support to play with

Same. I have a Pi Pico with PIO, though

> but the current "Golden Thread" correlation architecture fundamentally requires userspace + kernel cooperation that can't be fully offloaded.

Hard limit, I guess.

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