macOS/iOS have no recvmmsg(2), so the Mac client did one recv() syscall per
packet (non-allocating after the earlier fix, but still a syscall each — a
single-core wall at line rate that Moonlight avoids). Add the Darwin recvmsg_x(2)
batched-receive path (the recv counterpart of Linux recvmmsg): one syscall drains
up to RECV_BATCH datagrams into the reused ring. struct msghdr_x + the extern
aren't in the libc crate, so declared here (cfg target_vendor=apple).
Opt-in via PUNKTFUNK_RECVMSG_X (it's FFI we can't exercise off-Apple) with
auto-fallback to the tested scalar recv-loop on any unexpected error. Linux
recvmmsg + the non-Apple scalar loop are unchanged; apple.yml compiles the path.
Re GRO: Linux recv already batches via recvmmsg (32/syscall), so UDP GRO is only a
marginal add there and needs a recv-path redesign to split coalesced buffers —
deferred as low-ROI vs the Mac, which had no batching at all.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
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