Jak używać
- Skopiuj polecenie instalacji i sprawdź źródła przed instalacją we własnym środowisku agenta.
- W oryginale sprawdź wymagane narzędzia, dane dostępowe i obsługiwane środowiska.
- Opisz dane wejściowe i oczekiwany rezultat; porównaj wynik ze źródłami.
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill io-uringPrzed rozpoczęciem
- Instalacja nie obejmuje subskrypcji modelu, limitu API ani uprawnień do plików.
- Gwiazdki i instalacje pokazują aktywność, a nie niezależny test jakości lub bezpieczeństwa.
Oryginalny dokument Skill
Treść z repozytorium z zachowaniem nagłówków, przykładów, kodu, tabel, linków i obrazów.
io_uring
Purpose
Guide agents through Linux io_uring: the submission/completion queue model (SQE/CQE), liburing API, multi-shot accept/recv, provided buffer rings, fixed files and registered buffers, zero-copy send, Rust integration with tokio-uring, performance comparison with epoll, and security considerations.
When to Use
- Building a high-throughput network or disk server on Linux 5.1+
- Replacing epoll + thread pool with fewer syscalls
- Implementing multi-shot accept/recv for connection-heavy services
- Using zero-copy networking with
IORING_OP_SEND_ZC - Integrating async I/O in Rust via
tokio-uring - Evaluating io_uring vs epoll for your workload
Workflow
1. SQ/CQ model
Application Kernel
│ │
├── mmap SQ ring ───────────►│ submission queue (SQE)
├── mmap CQ ring ◄──────────│ completion queue (CQE)
├── io_uring_submit() ──────►│ processes SQEs
└── io_uring_wait_cqe() ◄──│ posts CQEsEach SQE describes one operation; each CQE reports result and user_data cookie.
2. Minimal liburing example
c
#include <liburing.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
int main(void) {
struct io_uring ring;
io_uring_queue_init(32, &ring, 0);
int fd = open("test.txt", O_RDONLY);
char buf[4096];
struct io_uring_sqe *sqe = io_uring_get_sqe(&ring);
io_uring_prep_read(sqe, fd, buf, sizeof(buf), 0);
io_uring_sqe_set_data(sqe, (void *)1);
io_uring_submit(&ring);
struct io_uring_cqe *cqe;
io_uring_wait_cqe(&ring, &cqe);
if (cqe->res >= 0)
printf("read %d bytes\n", cqe->res);
else
perror("read");
io_uring_cqe_seen(&ring, cqe);
io_uring_queue_exit(&ring);
close(fd);
return 0;
}bash
gcc -o uring_read uring_read.c -luring
./uring_read3. Common prep operations
| Function | Operation |
|---|---|
io_uring_prep_read | File read |
io_uring_prep_write | File write |
io_uring_prep_recv | Socket recv |
io_uring_prep_send | Socket send |
io_uring_prep_accept | Accept connection |
io_uring_prep_connect | Outbound connect |
io_uring_prep_poll_add | Poll fd |
io_uring_prep_timeout | Timeout/link timeout |
c
// Batch multiple SQEs before single submit
for (int i = 0; i < n; i++) {
sqe = io_uring_get_sqe(&ring);
io_uring_prep_read(sqe, fds[i], bufs[i], sizes[i], 0);
io_uring_sqe_set_data(sqe, (void *)(intptr_t)i);
}
io_uring_submit(&ring);4. Multi-shot operations
c
// Multi-shot accept — one SQE handles many connections
sqe = io_uring_get_sqe(&ring);
io_uring_prep_multishot_accept(sqe, listen_fd, NULL, NULL, 0);
io_uring_sqe_set_data(sqe, (void *)ACCEPT_COOKIE);
// Loop on CQEs until CQE_FLAG_MORE is clear
while (1) {
io_uring_wait_cqe(&ring, &cqe);
if (cqe->user_data == ACCEPT_COOKIE) {
int client_fd = cqe->res;
if (client_fd >= 0)
handle_client(client_fd);
if (!(cqe->flags & IORING_CQE_F_MORE))
break; // re-arm accept SQE
}
io_uring_cqe_seen(&ring, cqe);
}5. Provided buffer rings
c
#include <liburing.h>
#define BUF_GROUP 0
#define BUF_SIZE 4096
#define BUF_COUNT 64
struct io_uring_buf_ring *buf_ring;
char bufs[BUF_COUNT][BUF_SIZE];
// Setup buffer ring
buf_ring = io_uring_setup_buf_ring(&ring, BUF_COUNT, BUF_GROUP, 0, &ret);
for (int i = 0; i < BUF_COUNT; i++)
io_uring_buf_ring_add(buf_ring, bufs[i], BUF_SIZE, i, BUF_COUNT - 1 - i, 0);
io_uring_buf_ring_advance(buf_ring, BUF_COUNT);
// Recv with provided buffers
sqe = io_uring_get_sqe(&ring);
io_uring_prep_recv_multishot(sqe, sock_fd, NULL, 0, 0);
sqe->buf_group = BUF_GROUP;Kernel selects buffer from ring — eliminates per-recv buffer allocation.
6. Fixed files and registered buffers
c
// Register files — avoids per-op fd table lookup
int fds[64];
io_uring_register_files(&ring, fds, 64);
io_uring_prep_read(sqe, 0, buf, size, offset); // index 0, not fd
// Registered buffers — pinned, DMA-friendly
struct iovec iov = { .iov_base = buf, .iov_len = size };
io_uring_register_buffers(&ring, &iov, 1);
io_uring_prep_read_fixed(sqe, fd, buf, size, offset, 0);7. Zero-copy send
c
sqe = io_uring_get_sqe(&ring);
io_uring_prep_send_zc(sqe, sock_fd, data, len, 0, 0);
// May complete with IORING_CQE_F_MORE — wait for notification CQERequires kernel 6.0+, NIC/driver support. Falls back to copy mode if unavailable.
8. tokio-uring (Rust)
rust
use tokio_uring::fs::File;
#[tokio_uring::main]
async fn main() -> std::io::Result<()> {
let file = File::open("test.txt").await?;
let buf = vec![0u8; 4096];
let (res, buf) = file.read_at(buf, 0).await;
println!("read {} bytes", res?);
Ok(())
}bash
cargo add tokio-uring9. io_uring vs epoll
| Aspect | epoll | io_uring |
|---|---|---|
| Syscalls | epoll_wait + read/write per op | Batch SQEs, single submit |
| Buffer mgmt | App allocates | Provided buffers |
| Zero-copy | sendfile, manual | SEND_ZC built-in |
| Complexity | Lower | Higher |
| Kernel version | 2.6+ | 5.1+ (features vary) |
Choose io_uring when
├── Syscall overhead is measurable bottleneck
├── High connection count with multi-shot
└── Kernel 6.x+ with needed op support
Stay on epoll when
├── Simple app, portability matters
└── Team familiarity outweighs gains10. Security considerations
bash
# Restrict unprivileged io_uring (some distros disable by default)
sysctl kernel.io_uring_disabled # 0=enabled, 1=disabled, 2=allow registered
sysctl kernel.io_uring_group # gid allowed when disabled=2io_uring has been an attack surface — keep kernels patched; sandbox untrusted code.
Common Problems
| Symptom | Cause | Fix |
|---|---|---|
-EINVAL on prep | Op not supported on kernel | Check io_uring_get_probe() |
| Hang on wait_cqe | Missing submit | Call io_uring_submit after SQEs |
| Buffer not returned | Provided buffer not re-added | buf_ring_add after consuming |
| SEND_ZC incomplete | Need second CQE | Wait for IORING_CQE_F_MORE clear |
| Slower than epoll | Small batch size | Batch more SQEs; use SQPOLL |
| Permission denied | io_uring disabled | sysctl or run with capability |
Related Skills
skills/async-io/dpdk— kernel bypass alternative for networkingskills/async-io/af-xdp— XDP socket path for packet I/Oskills/observability/ebpf— trace io_uring eventsskills/rust/rust-async-internals— async model behind tokio-uringskills/profilers/strace-ltrace— syscall comparison vs epollskills/kernel/kernel-internals— kernel I/O subsystem context
