#319 - ARP Resolution

[cliffburdick]

Provide an API to users to do an ARP lookup manually and cache in their own routing tables.

[greptile-apps]

Confidence Score: 4/5

[Medium risk] Adds ARP resolution for raw Ethernet TX packets.

The PR should not merge until the required API and onboarding documentation is updated.

Summary

The PR adds a one-shot IPv4 next-hop MAC lookup for raw ibverbs, exposes it to C++ and Python, and uses it in raw TX examples and cross-host configuration. The latest update refreshes stale neighbors and adjusts the TX-only example and guidance. The public-API documentation mapping remains incomplete.

_{Reviews (6) · Last reviewed commit: "#319 - Refresh stale ARP and fix xhost c..."}

[dleshchev]

At PR head 2b7c63b, the committed cross-host TX config adds rx.flow_isolation: true without rx.queues. daqiri_config_validate reports invalid node; first invalid key: "queues" and rejects the YAML. Please make the committed config valid.

There is also a code-path concern: NUD_STALE is returned as usable before a neighbor refresh is triggered. Because raw TX bypasses Linux’s neighbor-use path, a later query after the peer MAC changes may return the old MAC. I did not reproduce a MAC change; please refresh stale entries before returning them.

Two pre-existing config values still block the documented example on the tested hardware: the committed RX flow ID 0 is rejected at init as zero or duplicate, and the committed TX batch_size: 10240 exceeds the device’s 4,096-packet maximum. With temporary config corrections, both an existing-neighbor run and a cold-ARP physical cross-host run sent and received exactly 778,240 packets each, with zero RX CQ errors, application ring drops, or NIC receive-buffer/PHY discards.

[cliffburdick]

Addressed in 8f1a263.

• Removed the invalid TX-only rx block; TX-only ports have no DAQIRI RX catch-all, so ARP remains on the kernel path without rx.flow_isolation. The ibverbs warning now applies only when DAQIRI RX queues exist.
• Changed the cross-host RX flow ID from 0 to 1.
• Capped both TX queue and benchmark batch sizes at 4096.
• Changed STALE/DELAY/PROBE handling so those entries are not returned immediately. The resolver first invalidates the cached neighbor, then uses NTF_USE to make Linux issue fresh broadcast ARP and waits for a confirmed address.
• Updated the destination-MAC documentation to distinguish TX-only interfaces from interfaces with DAQIRI RX queues and to document stale refresh behavior.

Verification:

• Both cross-host YAML files pass daqiri_config_validate.
• All checked-in config validation cases pass with the combined-engine validator.
• ibverbs-only and ibverbs+DPDK builds pass.
• CTest passes.
• Documentation reference check passes.
• An isolated veth test seeded a wrong STALE MAC and verified that resolution returned the peer current MAC after broadcast ARP, not the cached value.