[PATCH liburing 2/2] add a test for multishot downgrading

[Dylan Yudaken <dylany@meta.com>]

If the poll overflows we expect multishot poll to eventually downgrade to
single shot. Also the ordering of CQE's must be consistent, so check that.

Signed-off-by: Dylan Yudaken <dylany@meta.com>
---
 test/poll-mshot-overflow.c | 105 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 104 insertions(+), 1 deletion(-)

diff --git a/test/poll-mshot-overflow.c b/test/poll-mshot-overflow.c
index 431a337f19ae..0dc8ee5eb6f8 100644
--- a/test/poll-mshot-overflow.c
+++ b/test/poll-mshot-overflow.c
@@ -137,20 +137,123 @@ static int test(bool defer_taskrun)
 	return ret;
 }
 
+static int test_downgrade(bool support_defer)
+{
+	struct io_uring_cqe cqes[128];
+	struct io_uring_cqe *cqe;
+	struct io_uring_sqe *sqe;
+	struct io_uring ring;
+	int fds[2];
+	int ret, i, cqe_count, tmp = 0, more_cqe_count;
+
+	if (pipe(fds) != 0) {
+		perror("pipe");
+		return -1;
+	}
+
+	struct io_uring_params params = {
+		.flags = IORING_SETUP_CQSIZE,
+		.cq_entries = 2
+	};
+
+	ret = io_uring_queue_init_params(2, &ring, &params);
+	if (ret) {
+		fprintf(stderr, "queue init: %d\n", ret);
+		return -1;
+	}
+
+	sqe = io_uring_get_sqe(&ring);
+	if (!sqe) {
+		fprintf(stderr, "get sqe failed\n");
+		return -1;
+	}
+	io_uring_prep_poll_multishot(sqe, fds[0], POLLIN);
+	io_uring_sqe_set_data64(sqe, 1);
+	io_uring_submit(&ring);
+
+	for (i = 0; i < 8; i++) {
+		ret = write(fds[1], &tmp, sizeof(tmp));
+		if (ret != sizeof(tmp)) {
+			perror("write");
+			return -1;
+		}
+		ret = read(fds[0], &tmp, sizeof(tmp));
+		if (ret != sizeof(tmp)) {
+			perror("read");
+			return -1;
+		}
+	}
+
+	cqe_count = 0;
+	while (!io_uring_peek_cqe(&ring, &cqe)) {
+		cqes[cqe_count++] = *cqe;
+		io_uring_cqe_seen(&ring, cqe);
+	}
+
+	/* Some kernels might allow overflows to poll,
+	 * but if they didn't it should stop the MORE flag
+	 */
+	if (cqe_count < 3) {
+		fprintf(stderr, "too few cqes: %d\n", cqe_count);
+		return -1;
+	} else if (cqe_count == 8) {
+		more_cqe_count = cqe_count;
+		/* downgrade only available since support_defer */
+		if (support_defer) {
+			fprintf(stderr, "did not downgrade on overflow\n");
+			return -1;
+		}
+	} else {
+		more_cqe_count = cqe_count - 1;
+		cqe = &cqes[cqe_count - 1];
+		if (cqe->flags & IORING_CQE_F_MORE) {
+			fprintf(stderr, "incorrect MORE flag %x\n", cqe->flags);
+			return -1;
+		}
+	}
+
+	for (i = 0; i < more_cqe_count; i++) {
+		cqe = &cqes[i];
+		if (!(cqe->flags & IORING_CQE_F_MORE)) {
+			fprintf(stderr, "missing MORE flag\n");
+			return -1;
+		}
+		if (cqe->res < 0) {
+			fprintf(stderr, "bad res: %d\n", cqe->res);
+			return -1;
+		}
+	}
+
+	close(fds[0]);
+	close(fds[1]);
+	io_uring_queue_exit(&ring);
+	return 0;
+}
+
 int main(int argc, char *argv[])
 {
 	int ret;
+	bool support_defer;
 
 	if (argc > 1)
 		return T_EXIT_SKIP;
 
+	support_defer = t_probe_defer_taskrun();
+	ret = test_downgrade(support_defer);
+	if (ret) {
+		fprintf(stderr, "%s: test_downgrade(%d) failed\n", argv[0], support_defer);
+		return T_EXIT_FAIL;
+	}
+
 	ret = test(false);
+	if (ret == T_EXIT_SKIP)
+		return ret;
 	if (ret != T_EXIT_PASS) {
 		fprintf(stderr, "%s: test(false) failed\n", argv[0]);
 		return ret;
 	}
 
-	if (t_probe_defer_taskrun()) {
+	if (support_defer) {
 		ret = test(true);
 		if (ret != T_EXIT_PASS) {
 			fprintf(stderr, "%s: test(true) failed\n", argv[0]);
-- 
2.30.2