diff --git a/src/.gitignore b/src/.gitignore
index 355bed3..df7aff5 100644
--- a/src/.gitignore
+++ b/src/.gitignore
@@ -8,3 +8,4 @@
 /sg/dxfer-from-dev
 /sg/syzkaller1
 /zbdioctl
+/miniublk
diff --git a/src/Makefile b/src/Makefile
index 3b587f6..81c6541 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2,6 +2,10 @@ HAVE_C_HEADER = $(shell if echo "\#include <$(1)>" |		\
 		$(CC) -E - > /dev/null 2>&1; then echo "$(2)";	\
 		else echo "$(3)"; fi)
 
+HAVE_C_MACRO = $(shell if echo "#include <$(1)>" |	\
+		$(CC) -E - 2>&1 /dev/null | grep $(2) > /dev/null 2>&1; \
+		then echo 1;else echo 0; fi)
+
 C_TARGETS := \
 	loblksize \
 	loop_change_fd \
@@ -13,16 +17,27 @@ C_TARGETS := \
 	sg/syzkaller1 \
 	zbdioctl
 
+C_MINIUBLK := miniublk
+
+HAVE_LIBURING := $(call HAVE_C_MACRO,liburing.h,IORING_OP_URING_CMD)
+HAVE_UBLK_HEADER := $(call HAVE_C_HEADER,linux/ublk_cmd.h,1)
+
 CXX_TARGETS := \
 	discontiguous-io
 
+ifeq ($(HAVE_LIBURING)$(HAVE_UBLK_HEADER), 11)
+TARGETS := $(C_TARGETS) $(CXX_TARGETS) $(C_MINIUBLK)
+else
+$(info Skip $(C_MINIUBLK) build due to missing kernel header(v6.0+) or liburing(2.2+))
 TARGETS := $(C_TARGETS) $(CXX_TARGETS)
+endif
 
 CONFIG_DEFS := $(call HAVE_C_HEADER,linux/blkzoned.h,-DHAVE_LINUX_BLKZONED_H)
 
 override CFLAGS   := -O2 -Wall -Wshadow $(CFLAGS) $(CONFIG_DEFS)
 override CXXFLAGS := -O2 -std=c++11 -Wall -Wextra -Wshadow -Wno-sign-compare \
 		     -Werror $(CXXFLAGS) $(CONFIG_DEFS)
+MINIUBLK_FLAGS :=  -D_GNU_SOURCE -lpthread -luring
 
 all: $(TARGETS)
 
@@ -39,4 +54,7 @@ $(C_TARGETS): %: %.c
 $(CXX_TARGETS): %: %.cpp
 	$(CXX) $(CPPFLAGS) $(CXXFLAGS) -o $@ $^
 
+$(C_MINIUBLK): %: miniublk.c
+	$(CC) $(CFLAGS) $(MINIUBLK_FLAGS) -o $@ miniublk.c
+
 .PHONY: all clean install
diff --git a/src/miniublk.c b/src/miniublk.c
new file mode 100644
index 0000000..e84ba41
--- /dev/null
+++ b/src/miniublk.c
@@ -0,0 +1,1376 @@
+// SPDX-License-Identifier: GPL-3.0+
+// Copyright (C) 2023 Ming Lei
+
+/*
+ * io_uring based mini ublk implementation with null/loop target,
+ * for test purpose only.
+ *
+ * So please keep it clean & simple & reliable.
+ */
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <string.h>
+#include <pthread.h>
+#include <getopt.h>
+#include <limits.h>
+#include <sys/syscall.h>
+#include <sys/mman.h>
+#include <sys/ioctl.h>
+#include <liburing.h>
+#include <linux/ublk_cmd.h>
+
+#define CTRL_DEV		"/dev/ublk-control"
+#define UBLKC_DEV		"/dev/ublkc"
+#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 {
+	unsigned short cmd_op;
+#define CTRL_CMD_HAS_DATA	1
+#define CTRL_CMD_HAS_BUF	2
+	unsigned short 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;
+	int argc;
+	char **argv;
+	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;
+	int 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))
+
+#define ublk_assert(x)  do { \
+	if (!(x)) {     \
+		ublk_err("%s %d: assert!\n", __func__, __LINE__); \
+		assert(x);      \
+	}       \
+} while (0)
+
+static const struct ublk_tgt_ops *ublk_find_tgt(const char *name);
+
+static unsigned int ublk_dbg_mask = UBLK_LOG;
+
+static inline unsigned ilog2(unsigned x)
+{
+    return sizeof(unsigned) * 8 - 1 - __builtin_clz(x);
+}
+
+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_log(const char *fmt, ...)
+{
+	if (ublk_dbg_mask & UBLK_LOG) {
+		va_list ap;
+
+		va_start(ap, fmt);
+		vfprintf(stdout, 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->addr3;
+}
+
+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 inline 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;
+}
+
+int ublk_ctrl_stop_dev(struct ublk_dev *dev)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_CMD_STOP_DEV,
+	};
+	int ret;
+
+	ret = __ublk_ctrl_cmd(dev, &data);
+	return ret;
+}
+
+int ublk_ctrl_start_dev(struct ublk_dev *dev,
+		int daemon_pid)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_CMD_START_DEV,
+		.flags	= CTRL_CMD_HAS_DATA,
+	};
+	int ret;
+
+	dev->dev_info.ublksrv_pid = data.data[0] = daemon_pid;
+
+	ret = __ublk_ctrl_cmd(dev, &data);
+
+	return ret;
+}
+
+int ublk_ctrl_add_dev(struct ublk_dev *dev)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_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_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_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);
+}
+
+int ublk_ctrl_set_params(struct ublk_dev *dev,
+		struct ublk_params *params)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_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_params(struct ublk_dev *dev,
+		struct ublk_params *params)
+{
+	struct ublk_ctrl_cmd_data data = {
+		.cmd_op	= UBLK_CMD_GET_PARAMS,
+		.flags	= CTRL_CMD_HAS_BUF,
+		.addr = (__u64)params,
+		.len = sizeof(*params),
+	};
+	int ret;
+
+	params->len = sizeof(*params);
+
+	ret = __ublk_ctrl_cmd(dev, &data);
+	return ret;
+}
+
+static const char *ublk_dev_state_desc(struct ublk_dev *dev)
+{
+	switch (dev->dev_info.state) {
+	case UBLK_S_DEV_DEAD:
+		return "DEAD";
+	case UBLK_S_DEV_LIVE:
+		return "LIVE";
+	default:
+		return "UNKNOWN";
+	};
+}
+
+static void ublk_ctrl_dump(struct ublk_dev *dev, bool show_queue)
+{
+	struct ublksrv_ctrl_dev_info *info = &dev->dev_info;
+	int ret;
+	struct ublk_params p;
+
+	ret = ublk_ctrl_get_params(dev, &p);
+	if (ret < 0) {
+		ublk_err("failed to get params %m\n");
+		return;
+	}
+
+	ublk_log("dev id %d: nr_hw_queues %d queue_depth %d block size %d dev_capacity %lld\n",
+			info->dev_id,
+                        info->nr_hw_queues, info->queue_depth,
+                        1 << p.basic.logical_bs_shift, p.basic.dev_sectors);
+	ublk_log("\tmax rq size %d daemon pid %d flags 0x%llx state %s\n",
+                        info->max_io_buf_bytes,
+			info->ublksrv_pid, info->flags,
+			ublk_dev_state_desc(dev));
+	if (show_queue) {
+		int i;
+
+		for (i = 0; i < dev->dev_info.nr_hw_queues; i++)
+			ublk_log("\tqueue 0 tid: %d\n", dev->q[i].tid);
+	}
+	fflush(stdout);
+}
+
+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) {
+		ublk_err("control dev %s can't be opened: %m\n", CTRL_DEV);
+		exit(dev->ctrl_fd);
+	}
+	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\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\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_SQE128 | 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;
+
+	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);
+	else
+		ret = 0;
+
+	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_IO_COMMIT_AND_FETCH_REQ;
+	else if (io->flags & UBLKSRV_NEED_FETCH_RQ)
+		cmd_op = UBLK_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_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, 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 void ublk_queue_discard_io_pages(struct ublk_queue *q)
+{
+	const struct ublk_dev *dev = q->dev;
+	unsigned int io_buf_size = dev->dev_info.max_io_buf_bytes;
+	int i = 0;
+
+	for (i = 0; i < q->q_depth; i++)
+		madvise(q->ios[i].buf_addr, io_buf_size, MADV_DONTNEED);
+}
+
+static void ublk_queue_idle_enter(struct ublk_queue *q)
+{
+	if (q->state & UBLKSRV_QUEUE_IDLE)
+		return;
+
+	ublk_dbg(UBLK_DBG_QUEUE, "dev%d-q%d: enter idle %x\n",
+			q->dev->dev_info.dev_id, q->q_id, q->state);
+	ublk_queue_discard_io_pages(q);
+	q->state |= UBLKSRV_QUEUE_IDLE;
+}
+
+static void ublk_queue_idle_exit(struct ublk_queue *q)
+{
+	if (q->state & UBLKSRV_QUEUE_IDLE) {
+		ublk_dbg(UBLK_DBG_QUEUE, "dev%d-q%d: exit idle %x\n",
+			q->dev->dev_info.dev_id, q->q_id, q->state);
+		q->state &= ~UBLKSRV_QUEUE_IDLE;
+	}
+}
+
+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) {
+		ublk_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;
+	struct __kernel_timespec ts = {
+		.tv_sec = UBLKSRV_IO_IDLE_SECS,
+		.tv_nsec = 0
+        };
+	struct __kernel_timespec *tsp = (q->state & UBLKSRV_QUEUE_IDLE) ?
+		NULL : &ts;
+	struct io_uring_cqe *cqe;
+
+	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_timeout(&q->ring, &cqe, 1, tsp, NULL);
+	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));
+
+	if (!(q->state & UBLKSRV_QUEUE_STOPPING)) {
+		if (ret == -ETIME && reapped == 0 && ublk_queue_is_idle(q))
+			ublk_queue_idle_enter(q);
+		else
+			ublk_queue_idle_exit(q);
+	}
+	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;
+	}
+
+	/* submit all io commands to ublk driver */
+	ublk_submit_fetch_commands(q);
+
+	ublk_dbg(UBLK_DBG_QUEUE, "tid %d: ublk dev %d queue %d started\n",
+			gettid(),
+			dev_id, q->q_id);
+	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 (!dev)
+		return -ENOMEM;
+
+	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]);
+	}
+
+	ublk_set_parameters(dev);
+
+	/* everything is fine now, start us */
+	ret = ublk_ctrl_start_dev(dev, getpid());
+	if (ret < 0)
+		goto fail;
+
+	ublk_ctrl_get_info(dev);
+	ublk_ctrl_dump(dev, true);
+
+	/* 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 cmd_dev_add(int argc, char *argv[])
+{
+	static const struct option longopts[] = {
+		{ "type",		1,	NULL, 't' },
+		{ "number",		1,	NULL, 'n' },
+		{ "queues",		1,	NULL, 'q' },
+		{ "depth",		1,	NULL, 'd' },
+		{ "debug_mask",	1,	NULL, 0},
+		{ "quiet",	0,	NULL, 0},
+		{ NULL }
+	};
+	const struct ublk_tgt_ops *ops;
+	struct ublksrv_ctrl_dev_info *info;
+	struct ublk_dev *dev;
+	int ret, option_idx, opt;
+	const char *tgt_type = NULL;
+	int dev_id = -1;
+	unsigned nr_queues = 2, depth = UBLK_QUEUE_DEPTH;
+
+	while ((opt = getopt_long(argc, argv, "-:t:n:d:q:",
+				  longopts, &option_idx)) != -1) {
+		switch (opt) {
+		case 'n':
+			dev_id = strtol(optarg, NULL, 10);
+			break;
+		case 't':
+			tgt_type = optarg;
+			break;
+		case 'q':
+			nr_queues = strtol(optarg, NULL, 10);
+			break;
+		case 'd':
+			depth = strtol(optarg, NULL, 10);
+			break;
+		case 0:
+			if (!strcmp(longopts[option_idx].name, "debug_mask"))
+				ublk_dbg_mask = strtol(optarg, NULL, 16);
+			if (!strcmp(longopts[option_idx].name, "quiet"))
+				ublk_dbg_mask = 0;
+			break;
+		}
+	}
+
+	optind = 0;
+
+	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;
+	dev->tgt.argc = argc;
+	dev->tgt.argv = argv;
+
+	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;
+	}
+
+	ret = ublk_start_daemon(dev);
+	if (ret < 0) {
+		ublk_err("%s: can't start daemon id %d, type %s\n",
+				__func__, dev_id, tgt_type);
+		goto fail_del;
+	}
+fail_del:
+	ublk_ctrl_del_dev(dev);
+fail:
+	ublk_ctrl_deinit(dev);
+	return ret;
+}
+
+static int ublk_stop_io_daemon(const struct ublk_dev *dev)
+{
+	int daemon_pid = dev->dev_info.ublksrv_pid;
+	int cnt = 0, ret;
+
+	if (daemon_pid == -1)
+		return 0;
+
+	/* wait until daemon is exited, or timeout after 3 seconds */
+	do {
+		ret = kill(daemon_pid, 0);
+		if (ret)
+			break;
+		usleep(500000);
+		cnt++;
+	} while (!ret && cnt < 6);
+
+	ublk_dbg(UBLK_DBG_DEV, "%s: pid %d ret %d\n", __func__, daemon_pid, ret);
+
+	return ret != 0 ? 0 : -1;
+}
+
+static int __cmd_dev_del(int number, bool log)
+{
+	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;
+	}
+
+	ret = ublk_ctrl_stop_dev(dev);
+	if (ret < 0) {
+		if (log)
+			ublk_err("stop dev %d failed\n", number);
+		goto fail;
+	}
+
+	ret = ublk_stop_io_daemon(dev);
+	if (ret < 0) {
+		if (log)
+			ublk_err("stop daemon %d failed\n", number);
+	}
+
+	ublk_ctrl_del_dev(dev);
+fail:
+	ublk_ctrl_deinit(dev);
+	return ret;
+}
+
+static int cmd_dev_del(int argc, char *argv[])
+{
+	static const struct option longopts[] = {
+		{ "number",		1,	NULL, 'n' },
+		{ "all",		0,	NULL, 'a' },
+		{ "debug_mask",	1,	NULL, 0},
+		{ NULL }
+	};
+	int number = -2;
+	int opt, i, option_idx;
+
+	while ((opt = getopt_long(argc, argv, "n:a",
+				  longopts, &option_idx)) != -1) {
+		switch (opt) {
+		case 'a':
+			number = -1;
+			break;
+
+		case 'n':
+			number = strtol(optarg, NULL, 10);
+			break;
+		case 0:
+			if (!strcmp(longopts[option_idx].name, "debug_mask"))
+				ublk_dbg_mask = strtol(optarg, NULL, 16);
+			break;
+		}
+	}
+
+	if (number >= 0)
+		return __cmd_dev_del(number, true);
+	else if (number != -1) {
+		ublk_err("%s: pass wrong devid or not delete via -a\n");
+		return -EINVAL;
+	}
+
+	for (i = 0; i < 255; i++)
+		__cmd_dev_del(i, false);
+
+	return 0;
+}
+
+static int __cmd_dev_list(int number, bool log)
+{
+	struct ublk_dev *dev = ublk_ctrl_init();
+	int ret;
+
+	dev->dev_info.dev_id = number;
+
+	ret = ublk_ctrl_get_info(dev);
+	if (ret < 0) {
+		if (log)
+			ublk_err("%s: can't get dev info from %d: %d\n",
+					__func__, number, ret);
+	} else {
+		ublk_ctrl_dump(dev, false);
+	}
+
+	ublk_ctrl_deinit(dev);
+
+	return ret;
+}
+
+
+static int cmd_dev_list(int argc, char *argv[])
+{
+	static const struct option longopts[] = {
+		{ "number",		1,	NULL, 'n' },
+		{ "all",		0,	NULL, 'a' },
+		{ NULL }
+	};
+	int number = -1;
+	int opt, i;
+
+	while ((opt = getopt_long(argc, argv, "n:a",
+				  longopts, NULL)) != -1) {
+		switch (opt) {
+		case 'a':
+			break;
+
+		case 'n':
+			number = strtol(optarg, NULL, 10);
+			break;
+		}
+	}
+
+	if (number >= 0)
+		return __cmd_dev_list(number, true);
+
+	for (i = 0; i < 255; i++)
+		__cmd_dev_list(i, false);
+
+	return 0;
+}
+
+static int cmd_dev_help(int argc, char *argv[])
+{
+	printf("%s add -t {null|loop} [-q nr_queues] [-d depth] [-n dev_id] \n",
+			argv[0]);
+	printf("\t default: nr_queues=2(max 4), depth=128(max 128), dev_id=-1(auto allocation)\n");
+	printf("\t -t loop -f backing_file \n");
+	printf("\t -t null\n");
+	printf("%s del [-n dev_id] -a \n", argv[0]);
+	printf("\t -a delete all devices -n delete specified device\n");
+	printf("%s list [-n dev_id] -a \n", argv[0]);
+	printf("\t -a list all devices, -n list specified device, default -a \n");
+
+	return 0;
+}
+
+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;
+}
+
+static int loop_queue_tgt_io(struct ublk_queue *q, int tag)
+{
+	const struct ublksrv_io_desc *iod = ublk_get_iod(q, tag);
+	struct io_uring_sqe *sqe = io_uring_get_sqe(&q->ring);
+	unsigned ublk_op = ublksrv_get_op(iod);
+
+	if (!sqe)
+		return -ENOMEM;
+
+	switch (ublk_op) {
+	case UBLK_IO_OP_FLUSH:
+		io_uring_prep_sync_file_range(sqe, 1 /*fds[1]*/,
+				iod->nr_sectors << 9,
+				iod->start_sector << 9,
+				IORING_FSYNC_DATASYNC);
+		io_uring_sqe_set_flags(sqe, IOSQE_FIXED_FILE);
+		break;
+	case UBLK_IO_OP_WRITE_ZEROES:
+	case UBLK_IO_OP_DISCARD:
+		return -ENOTSUP;
+	case UBLK_IO_OP_READ:
+		io_uring_prep_read(sqe, 1 /*fds[1]*/,
+				(void *)iod->addr,
+				iod->nr_sectors << 9,
+				iod->start_sector << 9);
+		io_uring_sqe_set_flags(sqe, IOSQE_FIXED_FILE);
+		break;
+	case UBLK_IO_OP_WRITE:
+		io_uring_prep_write(sqe, 1 /*fds[1]*/,
+				(void *)iod->addr,
+				iod->nr_sectors << 9,
+				iod->start_sector << 9);
+		io_uring_sqe_set_flags(sqe, IOSQE_FIXED_FILE);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	q->io_inflight++;
+	/* bit63 marks us as tgt io */
+	sqe->user_data = build_user_data(tag, ublk_op, 0, 1);
+
+	ublk_dbg(UBLK_DBG_IO, "%s: tag %d ublk io %x %llx %u\n", __func__, tag,
+			iod->op_flags, iod->start_sector, iod->nr_sectors << 9);
+	return 1;
+}
+
+static int ublk_loop_queue_io(struct ublk_queue *q, int tag)
+{
+	int queued = loop_queue_tgt_io(q, tag);
+
+	if (queued < 0)
+		ublk_complete_io(q, tag, queued);
+
+	return 0;
+}
+
+static void ublk_loop_io_done(struct ublk_queue *q, int tag,
+		const struct io_uring_cqe *cqe)
+{
+	int cqe_tag = user_data_to_tag(cqe->user_data);
+
+	ublk_assert(tag == cqe_tag);
+	ublk_complete_io(q, tag, cqe->res);
+	q->io_inflight--;
+}
+
+static void ublk_loop_tgt_deinit(struct ublk_dev *dev)
+{
+	fsync(dev->fds[1]);
+	close(dev->fds[1]);
+}
+
+static int ublk_loop_tgt_init(struct ublk_dev *dev)
+{
+	static const struct option lo_longopts[] = {
+		{ "file",		1,	NULL, 'f' },
+		{ NULL }
+	};
+	unsigned long long bytes;
+	char **argv = dev->tgt.argv;
+	int argc = dev->tgt.argc;
+	char *file = NULL;
+	struct stat st;
+	int fd, opt;
+	struct ublk_params p = {
+		.types = UBLK_PARAM_TYPE_BASIC,
+		.basic = {
+			.logical_bs_shift	= 9,
+			.physical_bs_shift	= 12,
+			.io_opt_shift	= 12,
+			.io_min_shift	= 9,
+			.max_sectors = dev->dev_info.max_io_buf_bytes >> 9,
+		},
+	};
+
+	while ((opt = getopt_long(argc, argv, "-:f:",
+				  lo_longopts, NULL)) != -1) {
+		switch (opt) {
+		case 'f':
+			file = strdup(optarg);
+			break;
+		}
+	}
+
+	ublk_dbg(UBLK_DBG_DEV, "%s: file %s\n", __func__, file);
+
+	if (!file)
+		return -EINVAL;
+
+	fd = open(file, O_RDWR);
+	if (fd < 0) {
+		ublk_err( "%s: backing file %s can't be opened\n",
+				__func__, file);
+		return -EBADF;
+	}
+
+	if (fstat(fd, &st) < 0) {
+		close(fd);
+		return -EBADF;
+	}
+
+	if (S_ISBLK(st.st_mode)) {
+		unsigned int bs, pbs;
+
+		if (ioctl(fd, BLKGETSIZE64, &bytes) != 0)
+			return -EBADF;
+		if (ioctl(fd, BLKSSZGET, &bs) != 0)
+			return -1;
+		if (ioctl(fd, BLKPBSZGET, &pbs) != 0)
+			return -1;
+		p.basic.logical_bs_shift = ilog2(bs);
+		p.basic.physical_bs_shift = ilog2(pbs);
+	} else if (S_ISREG(st.st_mode)) {
+		bytes = st.st_size;
+	} else {
+		bytes = 0;
+	}
+
+	if (fcntl(fd, F_SETFL, O_DIRECT)) {
+		p.basic.logical_bs_shift = 9;
+		p.basic.physical_bs_shift = 12;
+		ublk_log("%s: ublk-loop fallback to buffered IO\n", __func__);
+	}
+
+	dev->tgt.dev_size = bytes;
+	p.basic.dev_sectors = bytes >> 9;
+	dev->fds[1] = fd;
+	dev->nr_fds += 1;
+	dev->tgt.params = p;
+
+	return 0;
+}
+
+const struct ublk_tgt_ops tgt_ops_list[] = {
+	{
+		.name = "null",
+		.init_tgt = ublk_null_tgt_init,
+		.queue_io = ublk_null_queue_io,
+	},
+
+	{
+		.name = "loop",
+		.init_tgt = ublk_loop_tgt_init,
+		.deinit_tgt = ublk_loop_tgt_deinit,
+		.queue_io = ublk_loop_queue_io,
+		.tgt_io_done = ublk_loop_io_done,
+	},
+};
+
+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;
+}
+
+int main(int argc, char *argv[])
+{
+	const char *cmd = argv[1];
+	int ret = -EINVAL;
+
+	if (argc == 1)
+		goto out;
+
+	if (!strcmp(cmd, "add"))
+		ret = cmd_dev_add(argc, argv);
+	else if (!strcmp(cmd, "del"))
+		ret = cmd_dev_del(argc, argv);
+	else if (!strcmp(cmd, "list"))
+		ret = cmd_dev_list(argc, argv);
+	else if (!strcmp(cmd, "help"))
+		ret = cmd_dev_help(argc, argv);
+out:
+	if (ret)
+		cmd_dev_help(argc, argv);
+
+	return ret;
+}
