test/cq-overflow.c - platform/external/liburing - Gitiles

 /* SPDX-License-Identifier: MIT */
 /*
  * Description: run various CQ ring overflow tests
  *
  */
 #include <errno.h>
 #include <stdio.h>
 #include <unistd.h>
 #include <stdlib.h>
 #include <string.h>
 #include <fcntl.h>

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

 #define FILE_SIZE	(256 * 1024)
 #define BS		4096
 #define BUFFERS		(FILE_SIZE / BS)

 static struct iovec *vecs;

 #define ENTRIES	8

 static int test_io(const char *file, unsigned long usecs, unsigned *drops, int fault)
 {
 	struct io_uring_sqe *sqe;
 	struct io_uring_cqe *cqe;
 	struct io_uring_params p;
 	unsigned reaped, total;
 	struct io_uring ring;
 	int nodrop, i, fd, ret;

 	fd = open(file, O_RDONLY | O_DIRECT);
 	if (fd < 0) {
 		perror("file open");
 		goto err;
 	}

 	memset(&p, 0, sizeof(p));
 	ret = io_uring_queue_init_params(ENTRIES, &ring, &p);
 	if (ret) {
 		fprintf(stderr, "ring create failed: %d\n", ret);
 		goto err;
 	}
 	nodrop = 0;
 	if (p.features & IORING_FEAT_NODROP)
 		nodrop = 1;

 	total = 0;
 	for (i = 0; i < BUFFERS / 2; i++) {
 		off_t offset;

 		sqe = io_uring_get_sqe(&ring);
 		if (!sqe) {
 			fprintf(stderr, "sqe get failed\n");
 			goto err;
 		}
 		offset = BS * (rand() % BUFFERS);
 		if (fault && i == ENTRIES + 4)
 			vecs[i].iov_base = NULL;
 		io_uring_prep_readv(sqe, fd, &vecs[i], 1, offset);

 		ret = io_uring_submit(&ring);
 		if (nodrop && ret == -EBUSY) {
 			*drops = 1;
 			total = i;
 			break;
 		} else if (ret != 1) {
 			fprintf(stderr, "submit got %d, wanted %d\n", ret, 1);
 			total = i;
 			break;
 		}
 		total++;
 	}

 	if (*drops)
 		goto reap_it;

 	usleep(usecs);

 	for (i = total; i < BUFFERS; i++) {
 		off_t offset;

 		sqe = io_uring_get_sqe(&ring);
 		if (!sqe) {
 			fprintf(stderr, "sqe get failed\n");
 			goto err;
 		}
 		offset = BS * (rand() % BUFFERS);
 		io_uring_prep_readv(sqe, fd, &vecs[i], 1, offset);

 		ret = io_uring_submit(&ring);
 		if (nodrop && ret == -EBUSY) {
 			*drops = 1;
 			break;
 		} else if (ret != 1) {
 			fprintf(stderr, "submit got %d, wanted %d\n", ret, 1);
 			break;
 		}
 		total++;
 	}

 reap_it:
 	reaped = 0;
 	do {
 		if (nodrop) {
 			/* nodrop should never lose events */
 			if (reaped == total)
 				break;
 		} else {
 			if (reaped + *ring.cq.koverflow == total)
 				break;
 		}
 		ret = io_uring_wait_cqe(&ring, &cqe);
 		if (ret) {
 			fprintf(stderr, "wait_cqe=%d\n", ret);
 			goto err;
 		}
 		if (cqe->res != BS) {
 			if (!(fault && cqe->res == -EFAULT)) {
 				fprintf(stderr, "cqe res %d, wanted %d\n",
 						cqe->res, BS);
 				goto err;
 			}
 		}
 		io_uring_cqe_seen(&ring, cqe);
 		reaped++;
 	} while (1);

 	if (!io_uring_peek_cqe(&ring, &cqe)) {
 		fprintf(stderr, "found unexpected completion\n");
 		goto err;
 	}

 	if (!nodrop) {
 		*drops = *ring.cq.koverflow;
 	} else if (*ring.cq.koverflow) {
 		fprintf(stderr, "Found %u overflows\n", *ring.cq.koverflow);
 		goto err;
 	}

 	io_uring_queue_exit(&ring);
 	close(fd);
 	return 0;
 err:
 	if (fd != -1)
 		close(fd);
 	io_uring_queue_exit(&ring);
 	return 1;
 }

 static int reap_events(struct io_uring *ring, unsigned nr_events, int do_wait)
 {
 	struct io_uring_cqe *cqe;
 	int i, ret = 0, seq = 0;

 	for (i = 0; i < nr_events; i++) {
 		if (do_wait)
 			ret = io_uring_wait_cqe(ring, &cqe);
 		else
 			ret = io_uring_peek_cqe(ring, &cqe);
 		if (ret) {
 			if (ret != -EAGAIN)
 				fprintf(stderr, "cqe peek failed: %d\n", ret);
 			break;
 		}
 		if (cqe->user_data != seq) {
 			fprintf(stderr, "cqe sequence out-of-order\n");
 			fprintf(stderr, "got %d, wanted %d\n", (int) cqe->user_data,
 					seq);
 			return -EINVAL;
 		}
 		seq++;
 		io_uring_cqe_seen(ring, cqe);
 	}

 	return i ? i : ret;
 }

 /*
  * Setup ring with CQ_NODROP and check we get -EBUSY on trying to submit new IO
  * on an overflown ring, and that we get all the events (even overflows) when
  * we finally reap them.
  */
 static int test_overflow_nodrop(void)
 {
 	struct __kernel_timespec ts;
 	struct io_uring_sqe *sqe;
 	struct io_uring_params p;
 	struct io_uring ring;
 	unsigned pending;
 	int ret, i, j;

 	memset(&p, 0, sizeof(p));
 	ret = io_uring_queue_init_params(4, &ring, &p);
 	if (ret) {
 		fprintf(stderr, "io_uring_queue_init failed %d\n", ret);
 		return 1;
 	}
 	if (!(p.features & IORING_FEAT_NODROP)) {
 		fprintf(stdout, "FEAT_NODROP not supported, skipped\n");
 		return 0;
 	}

 	ts.tv_sec = 0;
 	ts.tv_nsec = 10000000;

 	/* submit 4x4 SQEs, should overflow the ring by 8 */
 	pending = 0;
 	for (i = 0; i < 4; i++) {
 		for (j = 0; j < 4; j++) {
 			sqe = io_uring_get_sqe(&ring);
 			if (!sqe) {
 				fprintf(stderr, "get sqe failed\n");
 				goto err;
 			}

 			io_uring_prep_timeout(sqe, &ts, -1U, 0);
 			sqe->user_data = (i * 4) + j;
 		}

 		ret = io_uring_submit(&ring);
 		if (ret <= 0) {
 			if (ret == -EBUSY)
 				break;
 			fprintf(stderr, "sqe submit failed: %d, %d\n", ret, pending);
 			goto err;
 		}
 		pending += ret;
 	}

 	/* wait for timers to fire */
 	usleep(2 * 10000);

 	/*
 	 * We should have 16 pending CQEs now, 8 of them in the overflow list. Any
 	 * attempt to queue more IO should return -EBUSY
 	 */
 	sqe = io_uring_get_sqe(&ring);
 	if (!sqe) {
 		fprintf(stderr, "get sqe failed\n");
 		goto err;
 	}

 	io_uring_prep_nop(sqe);
 	ret = io_uring_submit(&ring);
 	if (ret != -EBUSY) {
 		fprintf(stderr, "expected sqe submit busy: %d\n", ret);
 		goto err;
 	}

 	/* reap the events we should have available */
 	ret = reap_events(&ring, pending, 1);
 	if (ret < 0) {
 		fprintf(stderr, "ret=%d\n", ret);
 		goto err;
 	}

 	if (*ring.cq.koverflow) {
 		fprintf(stderr, "cq ring overflow %d, expected 0\n",
 				*ring.cq.koverflow);
 		goto err;
 	}

 	io_uring_queue_exit(&ring);
 	return 0;
 err:
 	io_uring_queue_exit(&ring);
 	return 1;
 }

 /*
  * Submit some NOPs and watch if the overflow is correct
  */
 static int test_overflow(void)
 {
 	struct io_uring ring;
 	struct io_uring_params p;
 	struct io_uring_sqe *sqe;
 	unsigned pending;
 	int ret, i, j;

 	memset(&p, 0, sizeof(p));
 	ret = io_uring_queue_init_params(4, &ring, &p);
 	if (ret) {
 		fprintf(stderr, "io_uring_queue_init failed %d\n", ret);
 		return 1;
 	}

 	/* submit 4x4 SQEs, should overflow the ring by 8 */
 	pending = 0;
 	for (i = 0; i < 4; i++) {
 		for (j = 0; j < 4; j++) {
 			sqe = io_uring_get_sqe(&ring);
 			if (!sqe) {
 				fprintf(stderr, "get sqe failed\n");
 				goto err;
 			}

 			io_uring_prep_nop(sqe);
 			sqe->user_data = (i * 4) + j;
 		}

 		ret = io_uring_submit(&ring);
 		if (ret == 4) {
 			pending += 4;
 			continue;
 		}
 		if (p.features & IORING_FEAT_NODROP) {
 			if (ret == -EBUSY)
 				break;
 		}
 		fprintf(stderr, "sqe submit failed: %d\n", ret);
 		goto err;
 	}

 	/* we should now have 8 completions ready */
 	ret = reap_events(&ring, pending, 0);
 	if (ret < 0)
 		goto err;

 	if (!(p.features & IORING_FEAT_NODROP)) {
 		if (*ring.cq.koverflow != 8) {
 			fprintf(stderr, "cq ring overflow %d, expected 8\n",
 					*ring.cq.koverflow);
 			goto err;
 		}
 	}
 	io_uring_queue_exit(&ring);
 	return 0;
 err:
 	io_uring_queue_exit(&ring);
 	return 1;
 }

 /*
  * Test attempted submit with overflown cq ring that can't get flushed
  */
 static int test_overflow_nodrop_submit_ebusy(void)
 {
 	struct __kernel_timespec ts;
 	struct io_uring_sqe *sqe;
 	struct io_uring_params p;
 	struct io_uring ring;
 	unsigned pending;
 	int ret, i, j;

 	memset(&p, 0, sizeof(p));
 	ret = io_uring_queue_init_params(4, &ring, &p);
 	if (ret) {
 		fprintf(stderr, "io_uring_queue_init failed %d\n", ret);
 		return 1;
 	}
 	if (!(p.features & IORING_FEAT_NODROP)) {
 		fprintf(stdout, "FEAT_NODROP not supported, skipped\n");
 		return 0;
 	}

 	ts.tv_sec = 1;
 	ts.tv_nsec = 0;

 	/* submit 4x4 SQEs, should overflow the ring by 8 */
 	pending = 0;
 	for (i = 0; i < 4; i++) {
 		for (j = 0; j < 4; j++) {
 			sqe = io_uring_get_sqe(&ring);
 			if (!sqe) {
 				fprintf(stderr, "get sqe failed\n");
 				goto err;
 			}

 			io_uring_prep_timeout(sqe, &ts, -1U, 0);
 			sqe->user_data = (i * 4) + j;
 		}

 		ret = io_uring_submit(&ring);
 		if (ret <= 0) {
 			fprintf(stderr, "sqe submit failed: %d, %d\n", ret, pending);
 			goto err;
 		}
 		pending += ret;
 	}

 	/* wait for timers to fire */
 	usleep(1100000);

 	/*
 	 * We should have 16 pending CQEs now, 8 of them in the overflow list. Any
 	 * attempt to queue more IO should return -EBUSY
 	 */
 	sqe = io_uring_get_sqe(&ring);
 	if (!sqe) {
 		fprintf(stderr, "get sqe failed\n");
 		goto err;
 	}

 	io_uring_prep_nop(sqe);
 	ret = io_uring_submit(&ring);
 	if (ret != -EBUSY) {
 		fprintf(stderr, "expected sqe submit busy: %d\n", ret);
 		goto err;
 	}

 	/*
 	 * Now peek existing events so the CQ ring is empty, apart from the
 	 * backlog
 	 */
 	ret = reap_events(&ring, pending, 0);
 	if (ret < 0) {
 		fprintf(stderr, "ret=%d\n", ret);
 		goto err;
 	} else if (ret < 8) {
 		fprintf(stderr, "only found %d events, expected 8\n", ret);
 		goto err;
 	}

 	/*
 	 * We should now be able to submit our previous nop that's still
 	 * in the sq ring, as the kernel can flush the existing backlog
 	 * to the now empty CQ ring.
 	 */
 	ret = io_uring_submit(&ring);
 	if (ret != 1) {
 		fprintf(stderr, "submit got %d, expected 1\n", ret);
 		goto err;
 	}

 	io_uring_queue_exit(&ring);
 	return 0;
 err:
 	io_uring_queue_exit(&ring);
 	return 1;
 }


 int main(int argc, char *argv[])
 {
 	unsigned iters, drops;
 	unsigned long usecs;
 	int ret;

 	if (argc > 1)
 		return 0;

 	ret = test_overflow();
 	if (ret) {
 		printf("test_overflow failed\n");
 		return ret;
 	}

 	ret = test_overflow_nodrop();
 	if (ret) {
 		printf("test_overflow_nodrop failed\n");
 		return ret;
 	}

 	ret = test_overflow_nodrop_submit_ebusy();
 	if (ret) {
 		fprintf(stderr, "test_overflow_npdrop_submit_ebusy failed\n");
 		return ret;
 	}

 	t_create_file(".basic-rw", FILE_SIZE);

 	vecs = t_create_buffers(BUFFERS, BS);

 	iters = 0;
 	usecs = 1000;
 	do {
 		drops = 0;

 		if (test_io(".basic-rw", usecs, &drops, 0)) {
 			fprintf(stderr, "test_io nofault failed\n");
 			goto err;
 		}
 		if (drops)
 			break;
 		usecs = (usecs * 12) / 10;
 		iters++;
 	} while (iters < 40);

 	if (test_io(".basic-rw", usecs, &drops, 0)) {
 		fprintf(stderr, "test_io nofault failed\n");
 		goto err;
 	}

 	if (test_io(".basic-rw", usecs, &drops, 1)) {
 		fprintf(stderr, "test_io fault failed\n");
 		goto err;
 	}

 	unlink(".basic-rw");
 	return 0;
 err:
 	unlink(".basic-rw");
 	return 1;
 }
	/* SPDX-License-Identifier: MIT */
	/*
	* Description: run various CQ ring overflow tests
	*
	*/
	#include <errno.h>
	#include <stdio.h>
	#include <unistd.h>
	#include <stdlib.h>
	#include <string.h>
	#include <fcntl.h>

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

	#define FILE_SIZE (256 * 1024)
	#define BS 4096
	#define BUFFERS (FILE_SIZE / BS)

	static struct iovec *vecs;

	#define ENTRIES 8

	static int test_io(const char file, unsigned long usecs, unsigned drops, int fault)
	{
	struct io_uring_sqe *sqe;
	struct io_uring_cqe *cqe;
	struct io_uring_params p;
	unsigned reaped, total;
	struct io_uring ring;
	int nodrop, i, fd, ret;

	fd = open(file, O_RDONLY \| O_DIRECT);
	if (fd < 0) {
	perror("file open");
	goto err;
	}

	memset(&p, 0, sizeof(p));
	ret = io_uring_queue_init_params(ENTRIES, &ring, &p);
	if (ret) {
	fprintf(stderr, "ring create failed: %d\n", ret);
	goto err;
	}
	nodrop = 0;
	if (p.features & IORING_FEAT_NODROP)
	nodrop = 1;

	total = 0;
	for (i = 0; i < BUFFERS / 2; i++) {
	off_t offset;

	sqe = io_uring_get_sqe(&ring);
	if (!sqe) {
	fprintf(stderr, "sqe get failed\n");
	goto err;
	}
	offset = BS * (rand() % BUFFERS);
	if (fault && i == ENTRIES + 4)
	vecs[i].iov_base = NULL;
	io_uring_prep_readv(sqe, fd, &vecs[i], 1, offset);

	ret = io_uring_submit(&ring);
	if (nodrop && ret == -EBUSY) {
	*drops = 1;
	total = i;
	break;
	} else if (ret != 1) {
	fprintf(stderr, "submit got %d, wanted %d\n", ret, 1);
	total = i;
	break;
	}
	total++;
	}

	if (*drops)
	goto reap_it;

	usleep(usecs);

	for (i = total; i < BUFFERS; i++) {
	off_t offset;

	sqe = io_uring_get_sqe(&ring);
	if (!sqe) {
	fprintf(stderr, "sqe get failed\n");
	goto err;
	}
	offset = BS * (rand() % BUFFERS);
	io_uring_prep_readv(sqe, fd, &vecs[i], 1, offset);

	ret = io_uring_submit(&ring);
	if (nodrop && ret == -EBUSY) {
	*drops = 1;
	break;
	} else if (ret != 1) {
	fprintf(stderr, "submit got %d, wanted %d\n", ret, 1);
	break;
	}
	total++;
	}

	reap_it:
	reaped = 0;
	do {
	if (nodrop) {
	/* nodrop should never lose events */
	if (reaped == total)
	break;
	} else {
	if (reaped + *ring.cq.koverflow == total)
	break;
	}
	ret = io_uring_wait_cqe(&ring, &cqe);
	if (ret) {
	fprintf(stderr, "wait_cqe=%d\n", ret);
	goto err;
	}
	if (cqe->res != BS) {
	if (!(fault && cqe->res == -EFAULT)) {
	fprintf(stderr, "cqe res %d, wanted %d\n",
	cqe->res, BS);
	goto err;
	}
	}
	io_uring_cqe_seen(&ring, cqe);
	reaped++;
	} while (1);

	if (!io_uring_peek_cqe(&ring, &cqe)) {
	fprintf(stderr, "found unexpected completion\n");
	goto err;
	}

	if (!nodrop) {
	drops = ring.cq.koverflow;
	} else if (*ring.cq.koverflow) {
	fprintf(stderr, "Found %u overflows\n", *ring.cq.koverflow);
	goto err;
	}

	io_uring_queue_exit(&ring);
	close(fd);
	return 0;
	err:
	if (fd != -1)
	close(fd);
	io_uring_queue_exit(&ring);
	return 1;
	}

	static int reap_events(struct io_uring *ring, unsigned nr_events, int do_wait)
	{
	struct io_uring_cqe *cqe;
	int i, ret = 0, seq = 0;

	for (i = 0; i < nr_events; i++) {
	if (do_wait)
	ret = io_uring_wait_cqe(ring, &cqe);
	else
	ret = io_uring_peek_cqe(ring, &cqe);
	if (ret) {
	if (ret != -EAGAIN)
	fprintf(stderr, "cqe peek failed: %d\n", ret);
	break;
	}
	if (cqe->user_data != seq) {
	fprintf(stderr, "cqe sequence out-of-order\n");
	fprintf(stderr, "got %d, wanted %d\n", (int) cqe->user_data,
	seq);
	return -EINVAL;
	}
	seq++;
	io_uring_cqe_seen(ring, cqe);
	}

	return i ? i : ret;
	}

	/*
	* Setup ring with CQ_NODROP and check we get -EBUSY on trying to submit new IO
	* on an overflown ring, and that we get all the events (even overflows) when
	* we finally reap them.
	*/
	static int test_overflow_nodrop(void)
	{
	struct __kernel_timespec ts;
	struct io_uring_sqe *sqe;
	struct io_uring_params p;
	struct io_uring ring;
	unsigned pending;
	int ret, i, j;

	memset(&p, 0, sizeof(p));
	ret = io_uring_queue_init_params(4, &ring, &p);
	if (ret) {
	fprintf(stderr, "io_uring_queue_init failed %d\n", ret);
	return 1;
	}
	if (!(p.features & IORING_FEAT_NODROP)) {
	fprintf(stdout, "FEAT_NODROP not supported, skipped\n");
	return 0;
	}

	ts.tv_sec = 0;
	ts.tv_nsec = 10000000;

	/* submit 4x4 SQEs, should overflow the ring by 8 */
	pending = 0;
	for (i = 0; i < 4; i++) {
	for (j = 0; j < 4; j++) {
	sqe = io_uring_get_sqe(&ring);
	if (!sqe) {
	fprintf(stderr, "get sqe failed\n");
	goto err;
	}

	io_uring_prep_timeout(sqe, &ts, -1U, 0);
	sqe->user_data = (i * 4) + j;
	}

	ret = io_uring_submit(&ring);
	if (ret <= 0) {
	if (ret == -EBUSY)
	break;
	fprintf(stderr, "sqe submit failed: %d, %d\n", ret, pending);
	goto err;
	}
	pending += ret;
	}

	/* wait for timers to fire */
	usleep(2 * 10000);

	/*
	* We should have 16 pending CQEs now, 8 of them in the overflow list. Any
	* attempt to queue more IO should return -EBUSY
	*/
	sqe = io_uring_get_sqe(&ring);
	if (!sqe) {
	fprintf(stderr, "get sqe failed\n");
	goto err;
	}

	io_uring_prep_nop(sqe);
	ret = io_uring_submit(&ring);
	if (ret != -EBUSY) {
	fprintf(stderr, "expected sqe submit busy: %d\n", ret);
	goto err;
	}

	/* reap the events we should have available */
	ret = reap_events(&ring, pending, 1);
	if (ret < 0) {
	fprintf(stderr, "ret=%d\n", ret);
	goto err;
	}

	if (*ring.cq.koverflow) {
	fprintf(stderr, "cq ring overflow %d, expected 0\n",
	*ring.cq.koverflow);
	goto err;
	}

	io_uring_queue_exit(&ring);
	return 0;
	err:
	io_uring_queue_exit(&ring);
	return 1;
	}

	/*
	* Submit some NOPs and watch if the overflow is correct
	*/
	static int test_overflow(void)
	{
	struct io_uring ring;
	struct io_uring_params p;
	struct io_uring_sqe *sqe;
	unsigned pending;
	int ret, i, j;

	memset(&p, 0, sizeof(p));
	ret = io_uring_queue_init_params(4, &ring, &p);
	if (ret) {
	fprintf(stderr, "io_uring_queue_init failed %d\n", ret);
	return 1;
	}

	/* submit 4x4 SQEs, should overflow the ring by 8 */
	pending = 0;
	for (i = 0; i < 4; i++) {
	for (j = 0; j < 4; j++) {
	sqe = io_uring_get_sqe(&ring);
	if (!sqe) {
	fprintf(stderr, "get sqe failed\n");
	goto err;
	}

	io_uring_prep_nop(sqe);
	sqe->user_data = (i * 4) + j;
	}

	ret = io_uring_submit(&ring);
	if (ret == 4) {
	pending += 4;
	continue;
	}
	if (p.features & IORING_FEAT_NODROP) {
	if (ret == -EBUSY)
	break;
	}
	fprintf(stderr, "sqe submit failed: %d\n", ret);
	goto err;
	}

	/* we should now have 8 completions ready */
	ret = reap_events(&ring, pending, 0);
	if (ret < 0)
	goto err;

	if (!(p.features & IORING_FEAT_NODROP)) {
	if (*ring.cq.koverflow != 8) {
	fprintf(stderr, "cq ring overflow %d, expected 8\n",
	*ring.cq.koverflow);
	goto err;
	}
	}
	io_uring_queue_exit(&ring);
	return 0;
	err:
	io_uring_queue_exit(&ring);
	return 1;
	}

	/*
	* Test attempted submit with overflown cq ring that can't get flushed
	*/
	static int test_overflow_nodrop_submit_ebusy(void)
	{
	struct __kernel_timespec ts;
	struct io_uring_sqe *sqe;
	struct io_uring_params p;
	struct io_uring ring;
	unsigned pending;
	int ret, i, j;

	memset(&p, 0, sizeof(p));
	ret = io_uring_queue_init_params(4, &ring, &p);
	if (ret) {
	fprintf(stderr, "io_uring_queue_init failed %d\n", ret);
	return 1;
	}
	if (!(p.features & IORING_FEAT_NODROP)) {
	fprintf(stdout, "FEAT_NODROP not supported, skipped\n");
	return 0;
	}

	ts.tv_sec = 1;
	ts.tv_nsec = 0;

	/* submit 4x4 SQEs, should overflow the ring by 8 */
	pending = 0;
	for (i = 0; i < 4; i++) {
	for (j = 0; j < 4; j++) {
	sqe = io_uring_get_sqe(&ring);
	if (!sqe) {
	fprintf(stderr, "get sqe failed\n");
	goto err;
	}

	io_uring_prep_timeout(sqe, &ts, -1U, 0);
	sqe->user_data = (i * 4) + j;
	}

	ret = io_uring_submit(&ring);
	if (ret <= 0) {
	fprintf(stderr, "sqe submit failed: %d, %d\n", ret, pending);
	goto err;
	}
	pending += ret;
	}

	/* wait for timers to fire */
	usleep(1100000);

	/*
	* We should have 16 pending CQEs now, 8 of them in the overflow list. Any
	* attempt to queue more IO should return -EBUSY
	*/
	sqe = io_uring_get_sqe(&ring);
	if (!sqe) {
	fprintf(stderr, "get sqe failed\n");
	goto err;
	}

	io_uring_prep_nop(sqe);
	ret = io_uring_submit(&ring);
	if (ret != -EBUSY) {
	fprintf(stderr, "expected sqe submit busy: %d\n", ret);
	goto err;
	}

	/*
	* Now peek existing events so the CQ ring is empty, apart from the
	* backlog
	*/
	ret = reap_events(&ring, pending, 0);
	if (ret < 0) {
	fprintf(stderr, "ret=%d\n", ret);
	goto err;
	} else if (ret < 8) {
	fprintf(stderr, "only found %d events, expected 8\n", ret);
	goto err;
	}

	/*
	* We should now be able to submit our previous nop that's still
	* in the sq ring, as the kernel can flush the existing backlog
	* to the now empty CQ ring.
	*/
	ret = io_uring_submit(&ring);
	if (ret != 1) {
	fprintf(stderr, "submit got %d, expected 1\n", ret);
	goto err;
	}

	io_uring_queue_exit(&ring);
	return 0;
	err:
	io_uring_queue_exit(&ring);
	return 1;
	}


	int main(int argc, char *argv[])
	{
	unsigned iters, drops;
	unsigned long usecs;
	int ret;

	if (argc > 1)
	return 0;

	ret = test_overflow();
	if (ret) {
	printf("test_overflow failed\n");
	return ret;
	}

	ret = test_overflow_nodrop();
	if (ret) {
	printf("test_overflow_nodrop failed\n");
	return ret;
	}

	ret = test_overflow_nodrop_submit_ebusy();
	if (ret) {
	fprintf(stderr, "test_overflow_npdrop_submit_ebusy failed\n");
	return ret;
	}

	t_create_file(".basic-rw", FILE_SIZE);

	vecs = t_create_buffers(BUFFERS, BS);

	iters = 0;
	usecs = 1000;
	do {
	drops = 0;

	if (test_io(".basic-rw", usecs, &drops, 0)) {
	fprintf(stderr, "test_io nofault failed\n");
	goto err;
	}
	if (drops)
	break;
	usecs = (usecs * 12) / 10;
	iters++;
	} while (iters < 40);

	if (test_io(".basic-rw", usecs, &drops, 0)) {
	fprintf(stderr, "test_io nofault failed\n");
	goto err;
	}

	if (test_io(".basic-rw", usecs, &drops, 1)) {
	fprintf(stderr, "test_io fault failed\n");
	goto err;
	}

	unlink(".basic-rw");
	return 0;
	err:
	unlink(".basic-rw");
	return 1;
	}