Add SQ/CQ overflow tests

Signed-off-by: Jens Axboe <axboe@kernel.dk>

test/cq-full.c

@@ -0,0 +1,86 @@
+/*
+ * Description: test CQ ring overflow
+ *
+ */
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+
+#include "../src/liburing.h"
+
+static int queue_n_nops(struct io_uring *ring, int n)
+{
+	struct io_uring_sqe *sqe;
+	int i, ret;
+
+	for (i = 0; i < n; i++) {
+		sqe = io_uring_get_sqe(ring);
+		if (!sqe) {
+			printf("get sqe failed\n");
+			goto err;
+		}
+
+		io_uring_prep_nop(sqe);
+	}
+
+	ret = io_uring_submit(ring);
+	if (ret < n) {
+		printf("Submitted only %d\n", ret);
+		goto err;
+	} else if (ret < 0) {
+		printf("sqe submit failed: %d\n", ret);
+		goto err;
+	}
+
+	return 0;
+err:
+	return 1;
+}
+
+int main(int argc, char *argv[])
+{
+	struct io_uring_cqe *cqe;
+	struct io_uring ring;
+	int i, ret;
+
+	ret = io_uring_queue_init(4, &ring, 0);
+	if (ret) {
+		printf("ring setup failed\n");
+		return 1;
+
+	}
+
+	if (queue_n_nops(&ring, 4))
+		goto err;
+	if (queue_n_nops(&ring, 4))
+		goto err;
+	if (queue_n_nops(&ring, 4))
+		goto err;
+
+	i = 0;
+	do {
+		ret = io_uring_get_completion(&ring, &cqe);
+		if (ret < 0) {
+			printf("wait completion %d\n", ret);
+			goto err;
+		}
+		if (!cqe)
+			break;
+		i++;
+	} while (1);
+
+	if (i != 8 || *ring.cq.koverflow != 4) {
+		printf("CQ overflow fail: %d completions, %u overflow\n", i,
+				*ring.cq.koverflow);
+		goto err;
+	}
+
+	io_uring_queue_exit(&ring);
+	return 0;
+err:
+	io_uring_queue_exit(&ring);
+	return 1;
+}