io_uring_cat.c

#define _GNU_SOURCE
#define _POSIX_C_SOURCE 200809L
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <liburing.h>
#include <string.h>
#include <errno.h>

#define BUFSZ 8192

int main(int argc, char **argv)
{
#if !defined(__linux__)
    fprintf(stderr, "io_uring_cat is Linux-only\n");
    return 1;
#else
    if (argc < 2) {
        fprintf(stderr, "usage: %s file\n", argv[0]);
        return 1;
    }
    const char *path = argv[1];
    int fd = open(path, O_RDONLY);
    if (fd < 0) {
        perror("open");
        return 1;
    }
    struct io_uring ring;
    if (io_uring_queue_init(8, &ring, 0) < 0) {
        perror("io_uring_queue_init");
        close(fd);
        return 1;
    }
    char *buf = malloc(BUFSZ);
    if (!buf) {
        close(fd);
        io_uring_queue_exit(&ring);
        return 1;
    }
    off_t off = 0;
    for (;;) {
        struct io_uring_sqe *sqe = io_uring_get_sqe(&ring);
        if (!sqe) {
            io_uring_submit(&ring);
            continue;
        }
        io_uring_prep_read(sqe, fd, buf, BUFSZ, off);
        io_uring_sqe_set_data(sqe, buf);
        if (io_uring_submit(&ring) < 0) {
            perror("io_uring_submit");
            break;
        }
        struct io_uring_cqe *cqe;
        if (io_uring_wait_cqe(&ring, &cqe) < 0) {
            perror("io_uring_wait_cqe");
            break;
        }
        int res = cqe->res;
        if (res <= 0) {
            io_uring_cqe_seen(&ring, cqe);
            break;
        }
        write(STDOUT_FILENO, buf, res);
        off += res;
        io_uring_cqe_seen(&ring, cqe);
        if (res < BUFSZ) break;
    }
    free(buf);
    io_uring_queue_exit(&ring);
    close(fd);
    return 0;
#endif
}