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io_uring smoke test

End-to-end correctness check for the Linux io_uring IORING_OP_ACCEPT_MULTISHOT accept loop in zig/src/iouring.zig.

This is not a benchmark. It exists to prove that:

  1. zig/src/iouring.zig compiles cleanly for aarch64-linux-musl.
  2. std.os.linux.IoUring works on the kernel the test is run against.
  3. IORING_OP_ACCEPT_MULTISHOT actually delivers all expected accepts when N clients connect to a listen socket.

The smoke binary opens a TCP listener on 127.0.0.1:18080, runs the AcceptLoop on a worker thread, dials the listener N times from the main thread, and asserts the accept callback fired N times. Exits 0 on success, non-zero otherwise.

Run

Requires Apple container 0.11+ (or any compatible OCI runtime — set RUNTIME=docker / RUNTIME=podman). On macOS, start the container service first:

container system start
./bench/iouring/run.sh

The script:

  1. Cross-compiles iouring_smoke for aarch64-linux-musl on the host.
  2. Builds the OCI image from this directory.
  3. Runs the smoke binary inside a fresh container.

A passing run prints something like:

listening on 127.0.0.1:18080 (fd=3)
  client 1/16 connected
  ...
  client 16/16 connected
io_uring AcceptLoop saw 16 accepts (wanted >= 16)
OK
==> io_uring smoke test PASSED

The kernel version reported on a clean container run alpine:3.20 uname -a on macOS 26 / container 0.11 is Linux ... 6.18.5 ... aarch64, well above the 5.19 minimum for IORING_OP_ACCEPT_MULTISHOT.

Limitations

  • Only the accept loop is exercised. Per-connection recv / send over io_uring is not implemented yet — see the staged plan in zig/src/iouring.zig.
  • No request/response payload is sent; the test closes accepted fds immediately.
  • No latency or throughput numbers are produced. Per AGENTS.md, do not cite this script in any benchmark table or release note.