diff --git a/test/Makefile b/test/Makefile
index 6ac7dc1..e1729c0 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -221,6 +221,7 @@ test_srcs := \
 	wakeup-hang.c \
 	wq-aff.c \
 	xattr.c \
+	uring_cmd_ublk.c \
 	# EOL
 
 all_targets :=
diff --git a/test/uring_cmd_ublk.c b/test/uring_cmd_ublk.c
new file mode 100644
index 0000000..5924953
--- /dev/null
+++ b/test/uring_cmd_ublk.c
@@ -0,0 +1,1237 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Description: uring_cmd based ublk
+ *
+ * Covers cancellable uring_cmd feature.
+ */
+#include <unistd.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <string.h>
+#include <pthread.h>
+#include <limits.h>
+#include <poll.h>
+#include <liburing.h>
+#include <sys/syscall.h>
+#include <sys/mman.h>
+#include <sys/ioctl.h>
+#include <sys/inotify.h>
+#include <sys/wait.h>
+#include <linux/ublk_cmd.h>
+
+/****************** part 1: libublk ********************/
+
+#define CTRL_DEV		"/dev/ublk-control"
+#define UBLKC_DEV		"/dev/ublkc"
+#define UBLKB_DEV		"/dev/ublkb"
+#define UBLK_CTRL_RING_DEPTH            32
+
+/* queue idle timeout */
+#define UBLKSRV_IO_IDLE_SECS		20
+
+#define UBLK_IO_MAX_BYTES               65536
+#define UBLK_MAX_QUEUES                 4
+#define UBLK_QUEUE_DEPTH                128
+
+#define UBLK_DBG_DEV            (1U << 0)
+#define UBLK_DBG_QUEUE          (1U << 1)
+#define UBLK_DBG_IO_CMD         (1U << 2)
+#define UBLK_DBG_IO             (1U << 3)
+#define UBLK_DBG_CTRL_CMD       (1U << 4)
+#define UBLK_LOG                (1U << 5)
+
+struct ublk_dev;
+struct ublk_queue;
+
+struct ublk_ctrl_cmd_data {
+	__u32 cmd_op;
+#define CTRL_CMD_HAS_DATA	1
+#define CTRL_CMD_HAS_BUF	2
+	__u32 flags;
+
+	__u64 data[2];
+	__u64 addr;
+	__u32 len;
+};
+
+struct ublk_io {
+	char *buf_addr;
+
+#define UBLKSRV_NEED_FETCH_RQ		(1UL << 0)
+#define UBLKSRV_NEED_COMMIT_RQ_COMP	(1UL << 1)
+#define UBLKSRV_IO_FREE			(1UL << 2)
+	unsigned int flags;
+
+	unsigned int result;
+};
+
+struct ublk_tgt_ops {
+	const char *name;
+	int (*init_tgt)(struct ublk_dev *);
+	void (*deinit_tgt)(struct ublk_dev *);
+
+	int (*queue_io)(struct ublk_queue *, int tag);
+	void (*tgt_io_done)(struct ublk_queue *,
+			int tag, const struct io_uring_cqe *);
+};
+
+struct ublk_tgt {
+	unsigned long dev_size;
+	const struct ublk_tgt_ops *ops;
+	struct ublk_params params;
+};
+
+struct ublk_queue {
+	int q_id;
+	int q_depth;
+	unsigned int cmd_inflight;
+	unsigned int io_inflight;
+	struct ublk_dev *dev;
+	const struct ublk_tgt_ops *tgt_ops;
+	char *io_cmd_buf;
+	struct io_uring ring;
+	struct ublk_io ios[UBLK_QUEUE_DEPTH];
+#define UBLKSRV_QUEUE_STOPPING	(1U << 0)
+#define UBLKSRV_QUEUE_IDLE	(1U << 1)
+	unsigned state;
+	pid_t tid;
+	pthread_t thread;
+};
+
+struct ublk_dev {
+	struct ublk_tgt tgt;
+	struct ublksrv_ctrl_dev_info  dev_info;
+	struct ublk_queue q[UBLK_MAX_QUEUES];
+
+	int fds[2];	/* fds[0] points to /dev/ublkcN */
+	int nr_fds;
+	int ctrl_fd;
+	struct io_uring ring;
+};
+
+#ifndef offsetof
+#define offsetof(TYPE, MEMBER)  ((size_t)&((TYPE *)0)->MEMBER)
+#endif
+
+#ifndef container_of
+#define container_of(ptr, type, member) ({                              \
+	unsigned long __mptr = (unsigned long)(ptr);                    \
+	((type *)(__mptr - offsetof(type, member))); })
+#endif
+
+#define round_up(val, rnd) \
+	(((val) + ((rnd) - 1)) & ~((rnd) - 1))
+
+static unsigned int ublk_dbg_mask = 0;
+
+static const struct ublk_tgt_ops *ublk_find_tgt(const char *name);
+
+static inline int is_target_io(__u64 user_data)
+{
+	return (user_data & (1ULL << 63)) != 0;
+}
+
+static inline __u64 build_user_data(unsigned tag, unsigned op,
+		unsigned tgt_data, unsigned is_target_io)
+{
+	assert(!(tag >> 16) && !(op >> 8) && !(tgt_data >> 16));
+
+	return tag | (op << 16) | (tgt_data << 24) | (__u64)is_target_io << 63;
+}
+
+static inline unsigned int user_data_to_tag(__u64 user_data)
+{
+	return user_data & 0xffff;
+}
+
+static inline unsigned int user_data_to_op(__u64 user_data)
+{
+	return (user_data >> 16) & 0xff;
+}
+
+static void ublk_err(const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+}
+
+static void ublk_dbg(int level, const char *fmt, ...)
+{
+	if (level & ublk_dbg_mask) {
+		va_list ap;
+		va_start(ap, fmt);
+		vfprintf(stdout, fmt, ap);
+        }
+}
+
+static inline void *ublk_get_sqe_cmd(const struct io_uring_sqe *sqe)
+{
+	return (void *)&sqe->cmd;
+}
+
+static inline void ublk_mark_io_done(struct ublk_io *io, int res)
+{
+	io->flags |= (UBLKSRV_NEED_COMMIT_RQ_COMP | UBLKSRV_IO_FREE);
+	io->result = res;
+}
+
+static inline const struct ublksrv_io_desc *ublk_get_iod(
+                const struct ublk_queue *q, int tag)
+{
+        return (struct ublksrv_io_desc *)
+                &(q->io_cmd_buf[tag * sizeof(struct ublksrv_io_desc)]);
+}
+
+static inline void ublk_set_sqe_cmd_op(struct io_uring_sqe *sqe,
+		__u32 cmd_op)
+{
+        __u32 *addr = (__u32 *)&sqe->off;
+
+        addr[0] = cmd_op;
+        addr[1] = 0;
+}
+
+static inline int ublk_setup_ring(struct io_uring *r, int depth,
+		int cq_depth, unsigned flags)
+{
+	struct io_uring_params p;
+
+	memset(&p, 0, sizeof(p));
+	p.flags = flags | IORING_SETUP_CQSIZE;
+	p.cq_entries = cq_depth;
+
+	return io_uring_queue_init_params(depth, r, &p);
+}
+
+static void ublk_ctrl_init_cmd(struct ublk_dev *dev,
+		struct io_uring_sqe *sqe,
+		struct ublk_ctrl_cmd_data *data)
+{
+	struct ublksrv_ctrl_dev_info *info = &dev->dev_info;
+	struct ublksrv_ctrl_cmd *cmd = (struct ublksrv_ctrl_cmd *)ublk_get_sqe_cmd(sqe);
+
+	sqe->fd = dev->ctrl_fd;
+	sqe->opcode = IORING_OP_URING_CMD;
+	sqe->ioprio = 0;
+
+	if (data->flags & CTRL_CMD_HAS_BUF) {
+		cmd->addr = data->addr;
+		cmd->len = data->len;
+	}
+
+	if (data->flags & CTRL_CMD_HAS_DATA)
+		cmd->data[0] = data->data[0];
+
+	cmd->dev_id = info->dev_id;
+	cmd->queue_id = -1;
+
+	ublk_set_sqe_cmd_op(sqe, data->cmd_op);
+
+	io_uring_sqe_set_data(sqe, cmd);
+}
+
+static int __ublk_ctrl_cmd(struct ublk_dev *dev,
+		struct ublk_ctrl_cmd_data *data)
+{
+	struct io_uring_sqe *sqe;
+	struct io_uring_cqe *cqe;
+	int ret = -EINVAL;
+
+	sqe = io_uring_get_sqe(&dev->ring);
+	if (!sqe) {
+		ublk_err("%s: can't get sqe ret %d\n", __func__, ret);
+		return ret;
+	}
+
+	ublk_ctrl_init_cmd(dev, sqe, data);
+
+	ret = io_uring_submit(&dev->ring);
+	if (ret < 0) {
+		ublk_err("uring submit ret %d\n", ret);
+		return ret;
+	}
+
+	ret = io_uring_wait_cqe(&dev->ring, &cqe);
+	if (ret < 0) {
+		ublk_err("wait cqe: %s\n", strerror(-ret));
+		return ret;
+	}
+	io_uring_cqe_seen(&dev->ring, cqe);
+
+	return cqe->res;
+}
+
+static int ublk_ctrl_start_dev(struct ublk_dev *dev,
+		int daemon_pid)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_U_CMD_START_DEV,
+		.flags	= CTRL_CMD_HAS_DATA,
+	};
+
+	dev->dev_info.ublksrv_pid = data.data[0] = daemon_pid;
+
+	return __ublk_ctrl_cmd(dev, &data);
+}
+
+int ublk_ctrl_add_dev(struct ublk_dev *dev)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_U_CMD_ADD_DEV,
+		.flags	= CTRL_CMD_HAS_BUF,
+		.addr = (__u64)&dev->dev_info,
+		.len = sizeof(struct ublksrv_ctrl_dev_info),
+	};
+
+	return __ublk_ctrl_cmd(dev, &data);
+}
+
+int ublk_ctrl_del_dev(struct ublk_dev *dev)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op = UBLK_U_CMD_DEL_DEV,
+		.flags = 0,
+	};
+
+	return __ublk_ctrl_cmd(dev, &data);
+}
+
+int ublk_ctrl_get_info(struct ublk_dev *dev)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_U_CMD_GET_DEV_INFO,
+		.flags	= CTRL_CMD_HAS_BUF,
+		.addr = (__u64)&dev->dev_info,
+		.len = sizeof(struct ublksrv_ctrl_dev_info),
+	};
+
+	return __ublk_ctrl_cmd(dev, &data);
+}
+
+static int ublk_ctrl_set_params(struct ublk_dev *dev,
+		struct ublk_params *params)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_U_CMD_SET_PARAMS,
+		.flags	= CTRL_CMD_HAS_BUF,
+		.addr = (__u64)params,
+		.len = sizeof(*params),
+	};
+	params->len = sizeof(*params);
+	return __ublk_ctrl_cmd(dev, &data);
+}
+
+static int ublk_ctrl_get_features(struct ublk_dev *dev,
+		__u64 *features)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_U_CMD_GET_FEATURES,
+		.flags	= CTRL_CMD_HAS_BUF,
+		.addr = (__u64)features,
+		.len = sizeof(*features),
+	};
+
+	return __ublk_ctrl_cmd(dev, &data);
+}
+
+static void ublk_ctrl_deinit(struct ublk_dev *dev)
+{
+	close(dev->ctrl_fd);
+	free(dev);
+}
+
+static struct ublk_dev *ublk_ctrl_init()
+{
+	struct ublk_dev *dev = (struct ublk_dev *)calloc(1, sizeof(*dev));
+	struct ublksrv_ctrl_dev_info *info = &dev->dev_info;
+	int ret;
+
+	dev->ctrl_fd = open(CTRL_DEV, O_RDWR);
+	if (dev->ctrl_fd < 0)
+		return NULL;
+
+	info->max_io_buf_bytes = UBLK_IO_MAX_BYTES;
+
+	ret = ublk_setup_ring(&dev->ring, UBLK_CTRL_RING_DEPTH,
+			UBLK_CTRL_RING_DEPTH, IORING_SETUP_SQE128);
+	if (ret < 0) {
+		ublk_err("queue_init: %s\n", strerror(-ret));
+		free(dev);
+		return NULL;
+	}
+	dev->nr_fds = 1;
+
+	return dev;
+}
+
+static int ublk_queue_cmd_buf_sz(struct ublk_queue *q)
+{
+	int size =  q->q_depth * sizeof(struct ublksrv_io_desc);
+	unsigned int page_sz = getpagesize();
+
+	return round_up(size, page_sz);
+}
+
+static void ublk_queue_deinit(struct ublk_queue *q)
+{
+	int i;
+	int nr_ios = q->q_depth;
+
+	io_uring_unregister_ring_fd(&q->ring);
+
+	if (q->ring.ring_fd > 0) {
+		io_uring_unregister_files(&q->ring);
+		close(q->ring.ring_fd);
+		q->ring.ring_fd = -1;
+	}
+
+	if (q->io_cmd_buf)
+		munmap(q->io_cmd_buf, ublk_queue_cmd_buf_sz(q));
+
+	for (i = 0; i < nr_ios; i++)
+		free(q->ios[i].buf_addr);
+}
+
+static int ublk_queue_init(struct ublk_queue *q)
+{
+	struct ublk_dev *dev = q->dev;
+	int depth = dev->dev_info.queue_depth;
+	int i, ret = -1;
+	int cmd_buf_size, io_buf_size;
+	unsigned long off;
+	int ring_depth = depth, cq_depth = depth;
+
+	q->tgt_ops = dev->tgt.ops;
+	q->state = 0;
+	q->q_depth = depth;
+	q->cmd_inflight = 0;
+	q->tid = gettid();
+
+	cmd_buf_size = ublk_queue_cmd_buf_sz(q);
+	off = UBLKSRV_CMD_BUF_OFFSET +
+		q->q_id * (UBLK_MAX_QUEUE_DEPTH * sizeof(struct ublksrv_io_desc));
+	q->io_cmd_buf = (char *)mmap(0, cmd_buf_size, PROT_READ,
+			MAP_SHARED | MAP_POPULATE, dev->fds[0], off);
+	if (q->io_cmd_buf == MAP_FAILED) {
+		ublk_err("ublk dev %d queue %d map io_cmd_buf failed %m\n",
+				q->dev->dev_info.dev_id, q->q_id);
+		goto fail;
+	}
+
+	io_buf_size = dev->dev_info.max_io_buf_bytes;
+	for (i = 0; i < q->q_depth; i++) {
+		q->ios[i].buf_addr = NULL;
+
+		if (posix_memalign((void **)&q->ios[i].buf_addr,
+					getpagesize(), io_buf_size)) {
+			ublk_err("ublk dev %d queue %d io %d posix_memalign failed %m\n",
+					dev->dev_info.dev_id, q->q_id, i);
+			goto fail;
+		}
+		q->ios[i].flags = UBLKSRV_NEED_FETCH_RQ | UBLKSRV_IO_FREE;
+	}
+
+	ret = ublk_setup_ring(&q->ring, ring_depth, cq_depth,
+			IORING_SETUP_COOP_TASKRUN);
+	if (ret < 0) {
+		ublk_err("ublk dev %d queue %d setup io_uring failed %d\n",
+				q->dev->dev_info.dev_id, q->q_id, ret);
+		goto fail;
+	}
+
+	io_uring_register_ring_fd(&q->ring);
+
+	ret = io_uring_register_files(&q->ring, dev->fds, dev->nr_fds);
+	if (ret) {
+		ublk_err("ublk dev %d queue %d register files failed %d\n",
+				q->dev->dev_info.dev_id, q->q_id, ret);
+		goto fail;
+	}
+
+	return 0;
+ fail:
+	ublk_queue_deinit(q);
+	ublk_err("ublk dev %d queue %d failed\n",
+			dev->dev_info.dev_id, q->q_id);
+	return -ENOMEM;
+}
+
+static int ublk_dev_prep(struct ublk_dev *dev)
+{
+	int dev_id = dev->dev_info.dev_id;
+	char buf[64];
+	int ret = 0;
+
+	snprintf(buf, 64, "%s%d", UBLKC_DEV, dev_id);
+	dev->fds[0] = open(buf, O_RDWR);
+	if (dev->fds[0] < 0) {
+		ret = -EBADF;
+		ublk_err("can't open %s, ret %d\n", buf, dev->fds[0]);
+		goto fail;
+	}
+
+	if (dev->tgt.ops->init_tgt)
+		ret = dev->tgt.ops->init_tgt(dev);
+
+	return ret;
+fail:
+	close(dev->fds[0]);
+	return ret;
+}
+
+static void ublk_dev_unprep(struct ublk_dev *dev)
+{
+	if (dev->tgt.ops->deinit_tgt)
+		dev->tgt.ops->deinit_tgt(dev);
+	close(dev->fds[0]);
+}
+
+static int ublk_queue_io_cmd(struct ublk_queue *q,
+		struct ublk_io *io, unsigned tag)
+{
+	struct ublksrv_io_cmd *cmd;
+	struct io_uring_sqe *sqe;
+	unsigned int cmd_op = 0;
+	__u64 user_data;
+
+	/* only freed io can be issued */
+	if (!(io->flags & UBLKSRV_IO_FREE))
+		return 0;
+
+	/* we issue because we need either fetching or committing */
+	if (!(io->flags &
+		(UBLKSRV_NEED_FETCH_RQ | UBLKSRV_NEED_COMMIT_RQ_COMP)))
+		return 0;
+
+	if (io->flags & UBLKSRV_NEED_COMMIT_RQ_COMP)
+		cmd_op = UBLK_U_IO_COMMIT_AND_FETCH_REQ;
+	else if (io->flags & UBLKSRV_NEED_FETCH_RQ)
+		cmd_op = UBLK_U_IO_FETCH_REQ;
+
+	sqe = io_uring_get_sqe(&q->ring);
+	if (!sqe) {
+		ublk_err("%s: run out of sqe %d, tag %d\n",
+				__func__, q->q_id, tag);
+		return -1;
+	}
+
+	cmd = (struct ublksrv_io_cmd *)ublk_get_sqe_cmd(sqe);
+
+	if (cmd_op == UBLK_U_IO_COMMIT_AND_FETCH_REQ)
+		cmd->result = io->result;
+
+	/* These fields should be written once, never change */
+	ublk_set_sqe_cmd_op(sqe, cmd_op);
+	sqe->fd		= 0;	/* dev->fds[0] */
+	sqe->opcode	= IORING_OP_URING_CMD;
+	sqe->flags	= IOSQE_FIXED_FILE;
+	sqe->rw_flags	= 0;
+	cmd->tag	= tag;
+	cmd->addr	= (__u64)io->buf_addr;
+	cmd->q_id	= q->q_id;
+
+	user_data = build_user_data(tag, _IOC_NR(cmd_op), 0, 0);
+	io_uring_sqe_set_data64(sqe, user_data);
+
+	io->flags = 0;
+
+	q->cmd_inflight += 1;
+
+	ublk_dbg(UBLK_DBG_IO_CMD, "%s: (qid %d tag %u cmd_op %u) iof %x stopping %d\n",
+			__func__, q->q_id, tag, cmd_op,
+			io->flags, !!(q->state & UBLKSRV_QUEUE_STOPPING));
+	return 1;
+}
+
+static int ublk_complete_io(struct ublk_queue *q,
+		unsigned tag, int res)
+{
+	struct ublk_io *io = &q->ios[tag];
+
+	ublk_mark_io_done(io, res);
+
+	return ublk_queue_io_cmd(q, io, tag);
+}
+
+static void ublk_submit_fetch_commands(struct ublk_queue *q)
+{
+	int i = 0;
+
+	for (i = 0; i < q->q_depth; i++)
+		ublk_queue_io_cmd(q, &q->ios[i], i);
+}
+
+static int ublk_queue_is_idle(struct ublk_queue *q)
+{
+	return !io_uring_sq_ready(&q->ring) && !q->io_inflight;
+}
+
+static int ublk_queue_is_done(struct ublk_queue *q)
+{
+	return (q->state & UBLKSRV_QUEUE_STOPPING) && ublk_queue_is_idle(q);
+}
+
+static inline void ublksrv_handle_tgt_cqe(struct ublk_queue *q,
+		struct io_uring_cqe *cqe)
+{
+	unsigned tag = user_data_to_tag(cqe->user_data);
+
+	if (cqe->res < 0 && cqe->res != -EAGAIN)
+		ublk_err("%s: failed tgt io: res %d qid %u tag %u, cmd_op %u\n",
+			__func__, cqe->res, q->q_id,
+			user_data_to_tag(cqe->user_data),
+			user_data_to_op(cqe->user_data));
+
+	if (q->tgt_ops->tgt_io_done)
+		q->tgt_ops->tgt_io_done(q, tag, cqe);
+}
+
+static void ublk_handle_cqe(struct io_uring *r,
+		struct io_uring_cqe *cqe, void *data)
+{
+	struct ublk_queue *q = container_of(r, struct ublk_queue, ring);
+	unsigned tag = user_data_to_tag(cqe->user_data);
+	unsigned cmd_op = user_data_to_op(cqe->user_data);
+	int fetch = (cqe->res != UBLK_IO_RES_ABORT) &&
+		!(q->state & UBLKSRV_QUEUE_STOPPING);
+	struct ublk_io *io;
+
+	ublk_dbg(UBLK_DBG_IO_CMD, "%s: res %d (qid %d tag %u cmd_op %u target %d) stopping %d\n",
+			__func__, cqe->res, q->q_id, tag, cmd_op,
+			is_target_io(cqe->user_data),
+			(q->state & UBLKSRV_QUEUE_STOPPING));
+
+	/* Don't retrieve io in case of target io */
+	if (is_target_io(cqe->user_data)) {
+		ublksrv_handle_tgt_cqe(q, cqe);
+		return;
+	}
+
+	io = &q->ios[tag];
+	q->cmd_inflight--;
+
+	if (!fetch) {
+		q->state |= UBLKSRV_QUEUE_STOPPING;
+		io->flags &= ~UBLKSRV_NEED_FETCH_RQ;
+	}
+
+	if (cqe->res == UBLK_IO_RES_OK) {
+		assert(tag < q->q_depth);
+		q->tgt_ops->queue_io(q, tag);
+	} else {
+		/*
+		 * COMMIT_REQ will be completed immediately since no fetching
+		 * piggyback is required.
+		 *
+		 * Marking IO_FREE only, then this io won't be issued since
+		 * we only issue io with (UBLKSRV_IO_FREE | UBLKSRV_NEED_*)
+		 *
+		 * */
+		io->flags = UBLKSRV_IO_FREE;
+	}
+}
+
+static int ublk_reap_events_uring(struct io_uring *r)
+{
+	struct io_uring_cqe *cqe;
+	unsigned head;
+	int count = 0;
+
+	io_uring_for_each_cqe(r, head, cqe) {
+		ublk_handle_cqe(r, cqe, NULL);
+		count += 1;
+	}
+	io_uring_cq_advance(r, count);
+
+	return count;
+}
+
+static int ublk_process_io(struct ublk_queue *q)
+{
+	int ret, reapped;
+
+	ublk_dbg(UBLK_DBG_QUEUE, "dev%d-q%d: to_submit %d inflight cmd %u stopping %d\n",
+				q->dev->dev_info.dev_id,
+				q->q_id, io_uring_sq_ready(&q->ring),
+				q->cmd_inflight,
+				(q->state & UBLKSRV_QUEUE_STOPPING));
+
+	if (ublk_queue_is_done(q))
+		return -ENODEV;
+
+	ret = io_uring_submit_and_wait(&q->ring, 1);
+	reapped = ublk_reap_events_uring(&q->ring);
+
+	ublk_dbg(UBLK_DBG_QUEUE, "submit result %d, reapped %d stop %d idle %d\n",
+			ret, reapped, (q->state & UBLKSRV_QUEUE_STOPPING),
+			(q->state & UBLKSRV_QUEUE_IDLE));
+
+	return reapped;
+}
+
+static void *ublk_io_handler_fn(void *data)
+{
+	struct ublk_queue *q = data;
+	int dev_id = q->dev->dev_info.dev_id;
+	int ret;
+
+	ret = ublk_queue_init(q);
+	if (ret) {
+		ublk_err("ublk dev %d queue %d init queue failed\n",
+				dev_id, q->q_id);
+		return NULL;
+	}
+	ublk_dbg(UBLK_DBG_QUEUE, "tid %d: ublk dev %d queue %d started\n",
+			q->tid, dev_id, q->q_id);
+
+	/* submit all io commands to ublk driver */
+	ublk_submit_fetch_commands(q);
+	do {
+		if (ublk_process_io(q) < 0)
+			break;
+	} while (1);
+
+	ublk_dbg(UBLK_DBG_QUEUE, "ublk dev %d queue %d exited\n", dev_id, q->q_id);
+	ublk_queue_deinit(q);
+	return NULL;
+}
+
+static void ublk_set_parameters(struct ublk_dev *dev)
+{
+	int ret;
+
+	ret = ublk_ctrl_set_params(dev, &dev->tgt.params);
+	if (ret)
+		ublk_err("dev %d set basic parameter failed %d\n",
+				dev->dev_info.dev_id, ret);
+}
+
+static int ublk_start_daemon(struct ublk_dev *dev)
+{
+	int ret, i;
+	void *thread_ret;
+	const struct ublksrv_ctrl_dev_info *dinfo = &dev->dev_info;
+
+	daemon(1, 1);
+
+	ublk_dbg(UBLK_DBG_DEV, "%s enter\n", __func__);
+
+	ret = ublk_dev_prep(dev);
+	if (ret)
+		return ret;
+
+	for (i = 0; i < dinfo->nr_hw_queues; i++) {
+		dev->q[i].dev = dev;
+		dev->q[i].q_id = i;
+		pthread_create(&dev->q[i].thread, NULL,
+				ublk_io_handler_fn,
+				&dev->q[i]);
+	}
+
+	/* everything is fine now, start us */
+	ublk_set_parameters(dev);
+	ret = ublk_ctrl_start_dev(dev, getpid());
+	if (ret < 0) {
+		ublk_err("%s: ublk_ctrl_start_dev failed: %d\n", __func__, ret);
+		goto fail;
+	}
+
+	/* wait until we are terminated */
+	for (i = 0; i < dinfo->nr_hw_queues; i++)
+		pthread_join(dev->q[i].thread, &thread_ret);
+ fail:
+	ublk_dev_unprep(dev);
+	ublk_dbg(UBLK_DBG_DEV, "%s exit\n", __func__);
+
+	return ret;
+}
+
+static int wait_ublk_dev(char *dev_name, int evt_mask, unsigned timeout)
+{
+#define EV_SIZE (sizeof(struct inotify_event))
+#define EV_BUF_LEN (128 * (EV_SIZE + 16))
+	struct pollfd pfd;
+	int fd, wd;
+	int ret = -EINVAL;
+
+	fd = inotify_init();
+	if (fd < 0) {
+		ublk_dbg(UBLK_DBG_DEV, "%s: inotify init failed\n", __func__);
+		return fd;
+	}
+
+	wd = inotify_add_watch(fd, "/dev", evt_mask);
+	if (wd == -1) {
+		ublk_dbg(UBLK_DBG_DEV, "%s: add watch for /dev failed\n", __func__);
+		goto fail;
+	}
+
+	pfd.fd = fd;
+	pfd.events = POLL_IN;
+	while (1) {
+		int i = 0;
+		char buffer[EV_BUF_LEN];
+		ret = poll(&pfd, 1, 1000 * timeout);
+
+		if (ret == -1) {
+			ublk_err("%s: poll inotify failed: %d\n", __func__, ret);
+			goto rm_watch;
+		} else if (ret == 0) {
+			ublk_err("%s: poll inotify timeout\n", __func__);
+			ret = -ENOENT;
+			goto rm_watch;
+		}
+
+		ret = read(fd, buffer, EV_BUF_LEN);
+		if (ret < 0) {
+			ublk_err("%s: read inotify fd failed\n", __func__);
+			goto rm_watch;
+		}
+
+		while (i < ret) {
+			struct inotify_event *event = (struct inotify_event *)&buffer[i];
+
+			ublk_dbg(UBLK_DBG_DEV, "%s: inotify event %x %s\n",
+					__func__, event->mask, event->name);
+			if (event->mask & evt_mask) {
+				if (!strcmp(event->name, dev_name)) {
+					ret = 0;
+					goto rm_watch;
+				}
+			}
+			i += EV_SIZE + event->len;
+		}
+	}
+rm_watch:
+	inotify_rm_watch(fd, wd);
+fail:
+	close(fd);
+	return ret;
+}
+
+static int ublk_stop_io_daemon(const struct ublk_dev *dev)
+{
+	int daemon_pid = dev->dev_info.ublksrv_pid;
+	int dev_id = dev->dev_info.dev_id;
+	char ublkc[64];
+	int ret;
+
+	/*
+	 * Wait until ublk char device is closed, when our daemon is shutdown
+	 */
+	snprintf(ublkc, sizeof(ublkc), "%s%d", "ublkc", dev_id);
+	ret = wait_ublk_dev(ublkc, IN_CLOSE_WRITE, 10);
+	waitpid(dev->dev_info.ublksrv_pid, NULL, 0);
+	ublk_dbg(UBLK_DBG_DEV, "%s: pid %d dev_id %d ret %d\n",
+			__func__, daemon_pid, dev_id, ret);
+
+	return ret;
+}
+
+int cmd_dev_add(char *tgt_type, int *exp_id,
+		unsigned nr_queues, unsigned depth)
+{
+	const struct ublk_tgt_ops *ops;
+	struct ublksrv_ctrl_dev_info *info;
+	struct ublk_dev *dev;
+	int dev_id = *exp_id;
+	char ublkb[64];
+	int ret;
+
+	ops = ublk_find_tgt(tgt_type);
+	if (!ops) {
+		ublk_err("%s: no such tgt type, type %s\n",
+				__func__, tgt_type);
+		return -ENODEV;
+	}
+
+	if (nr_queues > UBLK_MAX_QUEUES || depth > UBLK_QUEUE_DEPTH) {
+		ublk_err("%s: invalid nr_queues or depth queues %u depth %u\n",
+				__func__, nr_queues, depth);
+		return -EINVAL;
+	}
+
+	dev = ublk_ctrl_init();
+	if (!dev) {
+		ublk_err("%s: can't alloc dev id %d, type %s\n",
+				__func__, dev_id, tgt_type);
+		return -ENOMEM;
+	}
+
+	info = &dev->dev_info;
+	info->dev_id = dev_id;
+        info->nr_hw_queues = nr_queues;
+        info->queue_depth = depth;
+	dev->tgt.ops = ops;
+
+	ret = ublk_ctrl_add_dev(dev);
+	if (ret < 0) {
+		ublk_err("%s: can't add dev id %d, type %s ret %d\n",
+				__func__, dev_id, tgt_type, ret);
+		goto fail;
+	}
+
+	switch (fork()) {
+	case -1:
+		goto fail;
+	case 0:
+		ublk_start_daemon(dev);
+		return 0;
+	}
+
+	/*
+	 * Wait until ublk disk is added, when our daemon is started
+	 * successfully
+	 */
+	snprintf(ublkb, sizeof(ublkb), "%s%u", "ublkb", dev->dev_info.dev_id);
+	ret = wait_ublk_dev(ublkb, IN_CREATE, 3);
+	if (ret < 0) {
+		ublk_err("%s: can't start daemon id %d, type %s\n",
+				__func__, dev_id, tgt_type);
+		ublk_ctrl_del_dev(dev);
+	} else {
+		*exp_id = dev->dev_info.dev_id;
+	}
+fail:
+	ublk_ctrl_deinit(dev);
+	return ret;
+}
+
+int cmd_dev_del_by_kill(int number)
+{
+	struct ublk_dev *dev;
+	int ret;
+
+	dev = ublk_ctrl_init();
+	dev->dev_info.dev_id = number;
+
+	ret = ublk_ctrl_get_info(dev);
+	if (ret < 0)
+		goto fail;
+
+	/* simulate one ublk daemon panic */
+	kill(dev->dev_info.ublksrv_pid, 9);
+
+	ret = ublk_stop_io_daemon(dev);
+	if (ret < 0)
+		ublk_err("%s: can't stop daemon id %d\n", __func__, number);
+	ublk_ctrl_del_dev(dev);
+fail:
+	if (ret >= 0)
+		ret = ublk_ctrl_get_info(dev);
+	ublk_ctrl_deinit(dev);
+
+	return (ret != 0) ? 0 : -EIO;
+}
+
+/****************** part 2: target implementation ********************/
+
+static int ublk_null_tgt_init(struct ublk_dev *dev)
+{
+	const struct ublksrv_ctrl_dev_info *info = &dev->dev_info;
+	unsigned long dev_size = 250UL << 30;
+
+	dev->tgt.dev_size = dev_size;
+	dev->tgt.params = (struct ublk_params) {
+		.types = UBLK_PARAM_TYPE_BASIC,
+		.basic = {
+			.logical_bs_shift	= 9,
+			.physical_bs_shift	= 12,
+			.io_opt_shift		= 12,
+			.io_min_shift		= 9,
+			.max_sectors		= info->max_io_buf_bytes >> 9,
+			.dev_sectors		= dev_size >> 9,
+		},
+	};
+
+	return 0;
+}
+
+static int ublk_null_queue_io(struct ublk_queue *q, int tag)
+{
+	const struct ublksrv_io_desc *iod = ublk_get_iod(q, tag);
+
+	ublk_complete_io(q, tag, iod->nr_sectors << 9);
+
+	return 0;
+}
+
+const struct ublk_tgt_ops tgt_ops_list[] = {
+	{
+		.name = "null",
+		.init_tgt = ublk_null_tgt_init,
+		.queue_io = ublk_null_queue_io,
+	},
+};
+
+static const struct ublk_tgt_ops *ublk_find_tgt(const char *name)
+{
+	const struct ublk_tgt_ops *ops;
+	int i;
+
+	if (name == NULL)
+		return NULL;
+
+	for (i = 0; sizeof(tgt_ops_list) / sizeof(*ops); i++)
+		if (strcmp(tgt_ops_list[i].name, name) == 0)
+			return &tgt_ops_list[i];
+	return NULL;
+}
+
+
+/****************** part 3: IO test over ublk disk ********************/
+
+#include "helpers.h"
+#include "liburing.h"
+#define BS		4096
+#define BUFFERS		128
+
+struct io_ctx {
+	int dev_id;
+	int write;
+	int seq;
+
+	/* output */
+	int res;
+	pthread_t handle;
+};
+
+static int __test_io(struct io_uring *ring, int fd, int write,
+		int seq, struct iovec *vecs, int exp_len, off_t start)
+{
+	struct io_uring_sqe *sqe;
+	struct io_uring_cqe *cqe;
+	int i, ret;
+	off_t offset;
+
+	offset = start;
+	for (i = 0; i < BUFFERS; i++) {
+		sqe = io_uring_get_sqe(ring);
+		if (!sqe) {
+			fprintf(stderr, "sqe get failed\n");
+			goto err;
+		}
+		if (!seq)
+			offset = start + BS * (rand() % BUFFERS);
+		if (write) {
+			io_uring_prep_write_fixed(sqe, fd, vecs[i].iov_base,
+						  vecs[i].iov_len,
+						  offset, i);
+		} else {
+			io_uring_prep_read_fixed(sqe, fd, vecs[i].iov_base,
+						 vecs[i].iov_len,
+						 offset, i);
+		}
+		sqe->user_data = i;
+		if (seq)
+			offset += BS;
+	}
+
+	ret = io_uring_submit(ring);
+	if (ret != BUFFERS) {
+		fprintf(stderr, "submit got %d, wanted %d\n", ret, BUFFERS);
+		goto err;
+	}
+
+	for (i = 0; i < BUFFERS; i++) {
+		ret = io_uring_wait_cqe(ring, &cqe);
+		if (ret) {
+			fprintf(stderr, "wait_cqe=%d\n", ret);
+			goto err;
+		}
+		if (exp_len == -1) {
+			int iov_len = vecs[cqe->user_data].iov_len;
+
+			if (cqe->res != iov_len) {
+				fprintf(stderr, "cqe res %d, wanted %d\n",
+					cqe->res, iov_len);
+				goto err;
+			}
+		} else if (cqe->res != exp_len) {
+			fprintf(stderr, "cqe res %d, wanted %d\n", cqe->res, exp_len);
+			goto err;
+		}
+		io_uring_cqe_seen(ring, cqe);
+	}
+
+	return 0;
+err:
+	return 1;
+}
+
+/* Run IO over ublk block device  */
+static int test_io(struct io_ctx *ctx)
+{
+	struct io_uring ring;
+	int ret, ring_flags = 0;
+	char buf[256];
+	int fd = -1;
+	off_t offset = 0;
+	unsigned long long bytes;
+	int open_flags = O_DIRECT;
+	struct iovec *vecs = t_create_buffers(BUFFERS, BS);
+
+	ret = t_create_ring(BUFFERS, &ring, ring_flags);
+	if (ret == T_SETUP_SKIP)
+		return 0;
+	if (ret != T_SETUP_OK) {
+		fprintf(stderr, "ring create failed: %d\n", ret);
+		return 1;
+	}
+
+	snprintf(buf, sizeof(buf), "%s%d", UBLKB_DEV, ctx->dev_id);
+
+	if (ctx->write)
+		open_flags |= O_WRONLY;
+	else
+		open_flags |= O_RDONLY;
+	fd = open(buf, open_flags);
+	if (fd < 0) {
+		if (errno == EINVAL)
+			return 0;
+		return 1;
+	}
+
+	if (ioctl(fd, BLKGETSIZE64, &bytes) != 0)
+		return 1;
+
+	ret = t_register_buffers(&ring, vecs, BUFFERS);
+	if (ret == T_SETUP_SKIP)
+		return 0;
+	if (ret != T_SETUP_OK) {
+		fprintf(stderr, "buffer reg failed: %d\n", ret);
+		return 1;
+	}
+
+	for (offset = 0; offset < bytes; offset += BS * BUFFERS) {
+		ret = __test_io(&ring, fd, ctx->write, ctx->seq, vecs, BS,
+				offset);
+		if (ret != T_SETUP_OK) {
+			fprintf(stderr, "/dev/ublkb%d read failed: offset %lu ret %d\n",
+					ctx->dev_id, offset, ret);
+			break;
+		}
+	}
+
+	close(fd);
+	io_uring_unregister_buffers(&ring);
+	io_uring_queue_exit(&ring);
+
+	return ret;
+}
+
+static void *test_io_fn(void *data)
+{
+	struct io_ctx *ctx = data;
+
+	ctx->res = test_io(ctx);
+
+	return data;
+}
+
+static void ignore_stderr()
+{
+	int devnull = open("/dev/null", O_WRONLY);
+
+	if (devnull >= 0) {
+		dup2(devnull, fileno(stderr));
+		close(devnull);
+	}
+}
+
+static int test_io_worker(int dev_id)
+{
+	const int nr_jobs = 4;
+	struct io_ctx ctx[nr_jobs];
+	int i, ret = 0;
+
+	for (i = 0; i < nr_jobs; i++) {
+		ctx[i].dev_id = dev_id;
+		ctx[i].write = (i & 0x1) ? 0 : 1;
+		ctx[i].seq = 1;
+
+		pthread_create(&ctx[i].handle, NULL, test_io_fn, &ctx[i]);
+	}
+
+	for (i = 0; i < nr_jobs; i++) {
+		pthread_join(ctx[i].handle, NULL);
+
+		if (!ret && ctx[i].res)
+			ret = ctx[i].res;
+	}
+
+	return ret;
+}
+
+/*
+ * Run IO over created ublk device, meantime delete this ublk device
+ *
+ * Cover cancellable uring_cmd
+ * */
+int test_del_ublk_with_io()
+{
+	const unsigned wait_ms = 200;
+	char *tgt_type = "null";
+	int dev_id = -1;
+	int ret, pid;
+
+	ret = cmd_dev_add(tgt_type, &dev_id, 2, BUFFERS);
+	if (ret != T_SETUP_OK) {
+		fprintf(stderr, "buffer reg failed: %d\n", ret);
+		return T_EXIT_FAIL;
+	}
+
+	switch ((pid = fork())) {
+	case -1:
+		fprintf(stderr, "fork failed\n");
+		return T_EXIT_FAIL;
+	case 0:
+		/* io error is expected since the parent is killing ublk */
+		ignore_stderr();
+		test_io_worker(dev_id);
+		return 0;
+	default:
+		/*
+		 * Wait a little while until ublk IO pipeline is warm up,
+		 * then try to shutdown ublk device by `kill -9 $ublk_daemon_pid`.
+		 *
+		 * cancellable uring_cmd code path can be covered in this way.
+		 */
+		usleep(wait_ms * 1000);
+		ret = cmd_dev_del_by_kill(dev_id);
+		waitpid(pid, NULL, 0);
+		return ret;
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	const int nr_loop = 4;
+	struct ublk_dev *dev;
+	__u64 features;
+	int ret, i;
+
+	dev = ublk_ctrl_init();
+	/* ublk isn't supported or the module isn't loaded */
+	if (!dev)
+		return T_EXIT_SKIP;
+
+	/* kernel doesn't support get_features */
+	ret = ublk_ctrl_get_features(dev, &features);
+	if (ret < 0)
+		return T_EXIT_SKIP;
+
+	if (!(features & UBLK_F_CMD_IOCTL_ENCODE))
+		return T_EXIT_SKIP;
+
+	for (i = 0; i < nr_loop; i++) {
+		if (test_del_ublk_with_io())
+			return T_EXIT_FAIL;
+	}
+	ublk_ctrl_deinit(dev);
+	return T_EXIT_PASS;
+}
