Re: [PATCH 4/4] io_uring/rsrc: send exact nr_segs for fixed buffer

[Jens Axboe <axboe@kernel.dk>]

On 4/17/25 7:41 AM, Jens Axboe wrote:
> I'll turn the test case into something we can add to liburing, and fold
> in that change.

Here's what I tested, fwiw, and it reliably blows up pre the fixup. I'll
turn it into a normal test case, and then folks can add more invariants
to this one if they wish.


#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#include <liburing.h>

static struct iovec vec;

static int read_it(struct io_uring *ring, int fd, int len, int off)
{
	struct io_uring_sqe *sqe;
	struct io_uring_cqe *cqe;
	int ret;

	sqe = io_uring_get_sqe(ring);
	io_uring_prep_read_fixed(sqe, fd, vec.iov_base + off, len, 0, 0);
	sqe->user_data = 1;

	io_uring_submit(ring);

	ret = io_uring_wait_cqe(ring, &cqe);
	if (ret) {
		fprintf(stderr, "wait %d\n", ret);
		return 1;
	}
	if (cqe->res < 0) {
		fprintf(stderr, "cqe res %s\n", strerror(-cqe->res));
		return 1;
	}
	if (cqe->res != len) {
		fprintf(stderr, "Bad read amount: %d\n", cqe->res);
		return 1;
	}
	io_uring_cqe_seen(ring, cqe);
	return 0;
}

static int test(struct io_uring *ring, int fd, int vec_off)
{
	struct iovec v = vec;
	int ret;

	v.iov_base += vec_off;
	v.iov_len -= vec_off;
	ret = io_uring_register_buffers(ring, &v, 1);
	if (ret) {
		fprintf(stderr, "Vec register: %d\n", ret);
		return 1;
	}

	ret = read_it(ring, fd, 4096, vec_off);
	if (ret) {
		fprintf(stderr, "4096 0 failed\n");
		return 1;
	}
	ret = read_it(ring, fd, 8192, 4096);
	if (ret) {
		fprintf(stderr, "8192 4096 failed\n");
		return 1;
	}
	ret = read_it(ring, fd, 4096, 4096);
	if (ret) {
		fprintf(stderr, "4096 4096 failed\n");
		return 1;
	}
	
	io_uring_unregister_buffers(ring);
	return 0;
}

int main(int argc, char *argv[])
{
	struct io_uring ring;
	int fd, ret;

	if (argc == 1) {
		printf("%s: <file>\n", argv[0]);
		return 1;
	}

	fd = open(argv[1], O_RDONLY | O_DIRECT);
	if (fd < 0) {
		perror("open");
		return 1;
	}

	posix_memalign(&vec.iov_base, 4096, 512*1024);
	vec.iov_len = 512*1024;

	io_uring_queue_init(32, &ring, 0);

	ret = test(&ring, fd, 0);
	if (ret) {
		fprintf(stderr, "test 0 failed\n");
		return 1;
	}

	ret = test(&ring, fd, 512);
	if (ret) {
		fprintf(stderr, "test 512 failed\n");
		return 1;
	}

	close(fd);
	io_uring_queue_exit(&ring);
	return 0;
}

-- 
Jens Axboe