Linux AIO example

test_aio.c

/**
 * Based on https://www.fsl.cs.sunysb.edu/~vass/linux-aio.txt
 * Compile gcc -Wall test_aio.c -o test_aio
 * Run rm -rf /tmp/testfile ;./iotest 
 */

#define _GNU_SOURCE		/* syscall() is not POSIX */

#include <stdio.h>		/* for perror() */
#include <unistd.h>		/* for syscall() */
#include <sys/syscall.h>	/* for __NR_* definitions */
#include <linux/aio_abi.h>	/* for AIO types and constants */
#include <fcntl.h>		/* O_RDWR */
#include <string.h>		/* memset() */
#include <inttypes.h>	/* uint64_t */

static  int io_setup(unsigned nr, aio_context_t *ctxp)
{
	return syscall(__NR_io_setup, nr, ctxp);
}

static int io_destroy(aio_context_t ctx) 
{
	return syscall(__NR_io_destroy, ctx);
}

static int io_submit(aio_context_t ctx, long nr,  struct iocb **iocbpp) 
{
	return syscall(__NR_io_submit, ctx, nr, iocbpp);
}

static int io_getevents(aio_context_t ctx, long min_nr, long max_nr,
		struct io_event *events, struct timespec *timeout)
{
	return syscall(__NR_io_getevents, ctx, min_nr, max_nr, events, timeout);
}

int main()
{
	aio_context_t ctx;
	struct iocb cb;
	struct iocb *cbs[1];
	char data[4096];
	struct io_event events[1];
	int ret;
	int fd;

	fd = open("/tmp/testfile", O_RDWR | O_CREAT);
	if (fd < 0) {
		perror("open error");
		return -1;
	}

	ctx = 0;

	ret = io_setup(128, &ctx);
	if (ret < 0) {
		perror("io_setup error");
		return -1;
	}

	/* setup I/O control block */
	memset(&cb, 0, sizeof(cb));
	cb.aio_fildes = fd;
	cb.aio_lio_opcode = IOCB_CMD_PWRITE;

	/* command-specific options */
	cb.aio_buf = (uint64_t)data;
	cb.aio_offset = 0;
	cb.aio_nbytes = 4096;

	cbs[0] = &cb;

	ret = io_submit(ctx, 1, cbs);
	if (ret != 1) {
		if (ret < 0)
  			perror("io_submit error");
		else
			fprintf(stderr, "could not sumbit IOs");
		return  -1;
	}

	/* get the reply */
	ret = io_getevents(ctx, 1, 1, events, NULL);
	printf("%d\n", ret);

	ret = io_destroy(ctx);
	if (ret < 0) {
		perror("io_destroy error");
		return -1;
	}
	return 0;
}