feat(fast_io): add io_uring LINKAT wrapper and kernel probe#3738
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Closes #1921, #1923. Adds a typed wrapper around `IORING_OP_LINKAT` (Linux 5.15+) so the receiver can submit hardlink creation alongside disk writes on the same ring instead of issuing a synchronous `linkat(2)` syscall per hardlinked file. The new `linkat` submodule mirrors the conventions used by `shared_ring::probe_poll_add` and `splice::is_splice_available`: - `LINKAT_MIN_KERNEL = (5, 15)` and `IORING_OP_LINKAT = 39` constants. - `linkat_supported()` short-circuits on `is_io_uring_available()`, builds a throwaway ring, and asks the kernel via `IORING_REGISTER_PROBE` whether opcode 39 is supported. The result is cached in a process-wide `OnceLock`. - `LinkAtArgs<'a>` borrows source/destination `&CStr` paths plus dirfds and `flags` so the compiler enforces the kernel's path lifetime contract. - `build_linkat_sqe` returns `io::ErrorKind::Unsupported` when the probe is `false`; `build_linkat_sqe_unchecked` exposes the encoder for unit tests. - `submit_linkat_blocking` builds a private 2-entry ring, submits the SQE, and returns the kernel's CQE result. The non-Linux stub in `io_uring_stub.rs` provides the same names with `linkat_supported() -> false` and `Unsupported` round-trips. Public re-exports in `crates/fast_io/src/lib.rs` and the Linux `io_uring` module make the API available to consumer crates. Tests: - Unit tests verify `opcode::LinkAt::CODE == 39`, the cached probe is idempotent, the unchecked SQE encoder accepts user_data, and the stub consistently returns `Unsupported`. - `tests/io_uring_linkat.rs` (Linux+`io_uring` feature) submits a real LINKAT, verifies the destination hardlink, and unlinks it; skips when the kernel does not advertise the opcode.
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* feat(fast_io): add io_uring LINKAT wrapper and kernel probe Closes #1921, #1923. Adds a typed wrapper around `IORING_OP_LINKAT` (Linux 5.15+) so the receiver can submit hardlink creation alongside disk writes on the same ring instead of issuing a synchronous `linkat(2)` syscall per hardlinked file. The new `linkat` submodule mirrors the conventions used by `shared_ring::probe_poll_add` and `splice::is_splice_available`: - `LINKAT_MIN_KERNEL = (5, 15)` and `IORING_OP_LINKAT = 39` constants. - `linkat_supported()` short-circuits on `is_io_uring_available()`, builds a throwaway ring, and asks the kernel via `IORING_REGISTER_PROBE` whether opcode 39 is supported. The result is cached in a process-wide `OnceLock`. - `LinkAtArgs<'a>` borrows source/destination `&CStr` paths plus dirfds and `flags` so the compiler enforces the kernel's path lifetime contract. - `build_linkat_sqe` returns `io::ErrorKind::Unsupported` when the probe is `false`; `build_linkat_sqe_unchecked` exposes the encoder for unit tests. - `submit_linkat_blocking` builds a private 2-entry ring, submits the SQE, and returns the kernel's CQE result. The non-Linux stub in `io_uring_stub.rs` provides the same names with `linkat_supported() -> false` and `Unsupported` round-trips. Public re-exports in `crates/fast_io/src/lib.rs` and the Linux `io_uring` module make the API available to consumer crates. Tests: - Unit tests verify `opcode::LinkAt::CODE == 39`, the cached probe is idempotent, the unchecked SQE encoder accepts user_data, and the stub consistently returns `Unsupported`. - `tests/io_uring_linkat.rs` (Linux+`io_uring` feature) submits a real LINKAT, verifies the destination hardlink, and unlinks it; skips when the kernel does not advertise the opcode. * fix(fast_io): use io::Error::other for clippy::io_other_error * fix(fast_io): use c"..." CStr literals to satisfy clippy manual_c_str_literals
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Summary
IORING_OP_LINKAT(Linux 5.15+) wrapper in a newcrates/fast_io/src/io_uring/linkat.rssubmodule with anOnceLock-cached kernel probe (linkat_supported), a borrowed-arg struct (LinkAtArgs<'a>over&CStrpaths), the gated builder (build_linkat_sqe), an unchecked encoder for tests, and a blocking submitter (submit_linkat_blocking).io_uring_stub.rs) withlinkat_supported() -> falseandUnsupportedround-trips so cross-platform call sites compile unchanged.crates/fast_io/src/io_uring/mod.rsandcrates/fast_io/src/lib.rs.Implementation notes
LINKAT_MIN_KERNEL = (5, 15)andIORING_OP_LINKAT = 39follow the kernel UAPI ininclude/uapi/linux/io_uring.h.linkat_supportedshort-circuits onis_io_uring_available()before building a throwaway ring +Probe, matching the convention inshared_ring::probe_poll_addandsplice::is_splice_available.LinkAtArgs<'a>ties source/destinationCStrlifetimes to the SQE so the compiler enforces the kernel's path-lifetime contract.Test plan
fmt+clippy, nextest stable, Windows, macOS, Linux muslUnsupportedround-triptests/io_uring_linkat.rssubmits a real LINKAT, verifies the hardlink, then removes the destination and confirms the source survives; skips when the kernel does not advertise the opcodeCompatibility
crates/fast_io/src/io_uring/mod.rsandcrates/fast_io/src/lib.rswith the parallel RENAMEAT2 PR; the module list and re-exports rebase cleanly.