Re: [PATCH] io_uring/openclose: add support for IORING_OP_FIXED_FD_INSTALL

[Jens Axboe <axboe@kernel.dk>]

Here's a sample test case showing the various transformations and
testing validity.

/* SPDX-License-Identifier: MIT */
/*
 * Description: test installing a direct descriptor into the regular
 *		file table
 *
 */
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>

#include "liburing.h"
#include "helpers.h"

static int no_fd_install;

static void io_uring_prep_fixed_fd_install(struct io_uring_sqe *sqe, int fd)
{
	memset(sqe, 0, sizeof(*sqe));
	sqe->opcode = IORING_OP_FIXED_FD_INSTALL;
	sqe->fd = fd;
}

int main(int argc, char *argv[])
{
	struct io_uring_sqe *sqe;
	struct io_uring_cqe *cqe;
	struct io_uring ring;
	int ret, fds[2];
	char buf[32];

	if (argc > 1)
		return T_EXIT_SKIP;

	ret = io_uring_queue_init(1, &ring, 0);
	if (ret) {
		fprintf(stderr, "ring setup failed: %d\n", ret);
		return T_EXIT_FAIL;
	}

	if (pipe(fds) < 0) {
		perror("pipe");
		return T_EXIT_FAIL;
	}

	/* register read side */
	ret = io_uring_register_files(&ring, &fds[0], 1);
	if (ret) {
		fprintf(stderr, "failed register files %d\n", ret);
		return T_EXIT_FAIL;
	}

	/* close normal descriptor */
	close(fds[0]);

	/* normal read should fail */
	ret = read(fds[0], buf, 1);
	if (ret != -1) {
		fprintf(stderr, "unexpected read ret %d\n", ret);
		return T_EXIT_FAIL;
	}
	if (errno != EBADF) {
		fprintf(stderr, "unexpected read failure %d\n", errno);
		return T_EXIT_FAIL;
	}

	/* verify we can read the data */
	sqe = io_uring_get_sqe(&ring);
	io_uring_prep_read(sqe, 0, buf, sizeof(buf), 0);
	sqe->flags = IOSQE_FIXED_FILE;
	io_uring_submit(&ring);

	/* put some data in the pipe */
	write(fds[1], "Hello", 5);

	ret = io_uring_wait_cqe(&ring, &cqe);
	if (ret) {
		fprintf(stderr, "wait cqe %d\n", ret);
		return T_EXIT_FAIL;
	}
	if (cqe->res != 5) {
		fprintf(stderr, "weird pipe read ret %d\n", cqe->res);
		return T_EXIT_FAIL;
	}
	io_uring_cqe_seen(&ring, cqe);

	/* fixed pipe read worked, now re-install as a regular fd */
	sqe = io_uring_get_sqe(&ring);
	io_uring_prep_fixed_fd_install(sqe, 0);
	sqe->flags = IOSQE_FIXED_FILE;
	io_uring_submit(&ring);

	ret = io_uring_wait_cqe(&ring, &cqe);
	if (ret) {
		fprintf(stderr, "wait cqe %d\n", ret);
		return T_EXIT_FAIL;
	}
	if (cqe->res == -EINVAL) {
		no_fd_install = 1;
		return T_EXIT_SKIP;
	}
	if (cqe->res < 0) {
		fprintf(stderr, "failed install fd: %d\n", cqe->res);
		return T_EXIT_FAIL;
	}
	/* stash new pipe read side fd in old spot */
	fds[0] = cqe->res;
	io_uring_cqe_seen(&ring, cqe);

	write(fds[1], "Hello", 5);

	/* normal pipe read should now work with new fd */
	ret = read(fds[0], buf, sizeof(buf));
	if (ret != 5) {
		fprintf(stderr, "unexpected read ret %d\n", ret);
		return T_EXIT_FAIL;
	}

	/* close fixed file */
	sqe = io_uring_get_sqe(&ring);
	io_uring_prep_close_direct(sqe, 0);
	io_uring_submit(&ring);

	ret = io_uring_wait_cqe(&ring, &cqe);
	if (ret) {
		fprintf(stderr, "wait cqe %d\n", ret);
		return T_EXIT_FAIL;
	}
	if (cqe->res) {
		fprintf(stderr, "close fixed fd %d\n", cqe->res);
		return T_EXIT_FAIL;
	}
	io_uring_cqe_seen(&ring, cqe);

	write(fds[1], "Hello", 5);

	/* normal pipe read should still work with new fd */
	ret = read(fds[0], buf, sizeof(buf));
	if (ret != 5) {
		fprintf(stderr, "unexpected read ret %d\n", ret);
		return T_EXIT_FAIL;
	}

	/* fixed fd pipe read should now fail */
	sqe = io_uring_get_sqe(&ring);
	io_uring_prep_read(sqe, 0, buf, sizeof(buf), 0);
	sqe->flags = IOSQE_FIXED_FILE;
	io_uring_submit(&ring);

	/* put some data in the pipe */
	write(fds[1], "Hello", 5);

	ret = io_uring_wait_cqe(&ring, &cqe);
	if (ret) {
		fprintf(stderr, "wait cqe %d\n", ret);
		return T_EXIT_FAIL;
	}
	if (cqe->res != -EBADF) {
		fprintf(stderr, "weird pipe read ret %d\n", cqe->res);
		return T_EXIT_FAIL;
	}
	io_uring_cqe_seen(&ring, cqe);

	return T_EXIT_PASS;
}

-- 
Jens Axboe