Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2939 insertions, 0 deletions

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
new file mode 100644
index 0000000000..630ddfe665
--- /dev/null
+++ b/drivers/block/ublk_drv.c
@@ -0,0 +1,2939 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Userspace block device - block device which IO is handled from userspace
+ *
+ * Take full use of io_uring passthrough command for communicating with
+ * ublk userspace daemon(ublksrvd) for handling basic IO request.
+ *
+ * Copyright 2022 Ming Lei <ming.lei@redhat.com>
+ *
+ * (part of code stolen from loop.c)
+ */
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/file.h>
+#include <linux/stat.h>
+#include <linux/errno.h>
+#include <linux/major.h>
+#include <linux/wait.h>
+#include <linux/blkdev.h>
+#include <linux/init.h>
+#include <linux/swap.h>
+#include <linux/slab.h>
+#include <linux/compat.h>
+#include <linux/mutex.h>
+#include <linux/writeback.h>
+#include <linux/completion.h>
+#include <linux/highmem.h>
+#include <linux/sysfs.h>
+#include <linux/miscdevice.h>
+#include <linux/falloc.h>
+#include <linux/uio.h>
+#include <linux/ioprio.h>
+#include <linux/sched/mm.h>
+#include <linux/uaccess.h>
+#include <linux/cdev.h>
+#include <linux/io_uring.h>
+#include <linux/blk-mq.h>
+#include <linux/delay.h>
+#include <linux/mm.h>
+#include <asm/page.h>
+#include <linux/task_work.h>
+#include <linux/namei.h>
+#include <linux/kref.h>
+#include <uapi/linux/ublk_cmd.h>
+
+#define UBLK_MINORS		(1U << MINORBITS)
+
+/* All UBLK_F_* have to be included into UBLK_F_ALL */
+#define UBLK_F_ALL (UBLK_F_SUPPORT_ZERO_COPY \
+		| UBLK_F_URING_CMD_COMP_IN_TASK \
+		| UBLK_F_NEED_GET_DATA \
+		| UBLK_F_USER_RECOVERY \
+		| UBLK_F_USER_RECOVERY_REISSUE \
+		| UBLK_F_UNPRIVILEGED_DEV \
+		| UBLK_F_CMD_IOCTL_ENCODE \
+		| UBLK_F_USER_COPY \
+		| UBLK_F_ZONED)
+
+/* All UBLK_PARAM_TYPE_* should be included here */
+#define UBLK_PARAM_TYPE_ALL                                \
+	(UBLK_PARAM_TYPE_BASIC | UBLK_PARAM_TYPE_DISCARD | \
+	 UBLK_PARAM_TYPE_DEVT | UBLK_PARAM_TYPE_ZONED)
+
+struct ublk_rq_data {
+	struct llist_node node;
+
+	struct kref ref;
+	__u64 sector;
+	__u32 operation;
+	__u32 nr_zones;
+};
+
+struct ublk_uring_cmd_pdu {
+	struct ublk_queue *ubq;
+};
+
+/*
+ * io command is active: sqe cmd is received, and its cqe isn't done
+ *
+ * If the flag is set, the io command is owned by ublk driver, and waited
+ * for incoming blk-mq request from the ublk block device.
+ *
+ * If the flag is cleared, the io command will be completed, and owned by
+ * ublk server.
+ */
+#define UBLK_IO_FLAG_ACTIVE	0x01
+
+/*
+ * IO command is completed via cqe, and it is being handled by ublksrv, and
+ * not committed yet
+ *
+ * Basically exclusively with UBLK_IO_FLAG_ACTIVE, so can be served for
+ * cross verification
+ */
+#define UBLK_IO_FLAG_OWNED_BY_SRV 0x02
+
+/*
+ * IO command is aborted, so this flag is set in case of
+ * !UBLK_IO_FLAG_ACTIVE.
+ *
+ * After this flag is observed, any pending or new incoming request
+ * associated with this io command will be failed immediately
+ */
+#define UBLK_IO_FLAG_ABORTED 0x04
+
+/*
+ * UBLK_IO_FLAG_NEED_GET_DATA is set because IO command requires
+ * get data buffer address from ublksrv.
+ *
+ * Then, bio data could be copied into this data buffer for a WRITE request
+ * after the IO command is issued again and UBLK_IO_FLAG_NEED_GET_DATA is unset.
+ */
+#define UBLK_IO_FLAG_NEED_GET_DATA 0x08
+
+struct ublk_io {
+	/* userspace buffer address from io cmd */
+	__u64	addr;
+	unsigned int flags;
+	int res;
+
+	struct io_uring_cmd *cmd;
+};
+
+struct ublk_queue {
+	int q_id;
+	int q_depth;
+
+	unsigned long flags;
+	struct task_struct	*ubq_daemon;
+	char *io_cmd_buf;
+
+	struct llist_head	io_cmds;
+
+	unsigned long io_addr;	/* mapped vm address */
+	unsigned int max_io_sz;
+	bool force_abort;
+	bool timeout;
+	unsigned short nr_io_ready;	/* how many ios setup */
+	struct ublk_device *dev;
+	struct ublk_io ios[];
+};
+
+#define UBLK_DAEMON_MONITOR_PERIOD	(5 * HZ)
+
+struct ublk_device {
+	struct gendisk		*ub_disk;
+
+	char	*__queues;
+
+	unsigned int	queue_size;
+	struct ublksrv_ctrl_dev_info	dev_info;
+
+	struct blk_mq_tag_set	tag_set;
+
+	struct cdev		cdev;
+	struct device		cdev_dev;
+
+#define UB_STATE_OPEN		0
+#define UB_STATE_USED		1
+#define UB_STATE_DELETED	2
+	unsigned long		state;
+	int			ub_number;
+
+	struct mutex		mutex;
+
+	spinlock_t		mm_lock;
+	struct mm_struct	*mm;
+
+	struct ublk_params	params;
+
+	struct completion	completion;
+	unsigned int		nr_queues_ready;
+	unsigned int		nr_privileged_daemon;
+
+	/*
+	 * Our ubq->daemon may be killed without any notification, so
+	 * monitor each queue's daemon periodically
+	 */
+	struct delayed_work	monitor_work;
+	struct work_struct	quiesce_work;
+	struct work_struct	stop_work;
+};
+
+/* header of ublk_params */
+struct ublk_params_header {
+	__u32	len;
+	__u32	types;
+};
+
+static inline unsigned int ublk_req_build_flags(struct request *req);
+static inline struct ublksrv_io_desc *ublk_get_iod(struct ublk_queue *ubq,
+						   int tag);
+
+static inline bool ublk_dev_is_user_copy(const struct ublk_device *ub)
+{
+	return ub->dev_info.flags & UBLK_F_USER_COPY;
+}
+
+static inline bool ublk_dev_is_zoned(const struct ublk_device *ub)
+{
+	return ub->dev_info.flags & UBLK_F_ZONED;
+}
+
+static inline bool ublk_queue_is_zoned(struct ublk_queue *ubq)
+{
+	return ubq->flags & UBLK_F_ZONED;
+}
+
+#ifdef CONFIG_BLK_DEV_ZONED
+
+static int ublk_get_nr_zones(const struct ublk_device *ub)
+{
+	const struct ublk_param_basic *p = &ub->params.basic;
+
+	/* Zone size is a power of 2 */
+	return p->dev_sectors >> ilog2(p->chunk_sectors);
+}
+
+static int ublk_revalidate_disk_zones(struct ublk_device *ub)
+{
+	return blk_revalidate_disk_zones(ub->ub_disk, NULL);
+}
+
+static int ublk_dev_param_zoned_validate(const struct ublk_device *ub)
+{
+	const struct ublk_param_zoned *p = &ub->params.zoned;
+	int nr_zones;
+
+	if (!ublk_dev_is_zoned(ub))
+		return -EINVAL;
+
+	if (!p->max_zone_append_sectors)
+		return -EINVAL;
+
+	nr_zones = ublk_get_nr_zones(ub);
+
+	if (p->max_active_zones > nr_zones)
+		return -EINVAL;
+
+	if (p->max_open_zones > nr_zones)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int ublk_dev_param_zoned_apply(struct ublk_device *ub)
+{
+	const struct ublk_param_zoned *p = &ub->params.zoned;
+
+	disk_set_zoned(ub->ub_disk, BLK_ZONED_HM);
+	blk_queue_flag_set(QUEUE_FLAG_ZONE_RESETALL, ub->ub_disk->queue);
+	blk_queue_required_elevator_features(ub->ub_disk->queue,
+					     ELEVATOR_F_ZBD_SEQ_WRITE);
+	disk_set_max_active_zones(ub->ub_disk, p->max_active_zones);
+	disk_set_max_open_zones(ub->ub_disk, p->max_open_zones);
+	blk_queue_max_zone_append_sectors(ub->ub_disk->queue, p->max_zone_append_sectors);
+
+	ub->ub_disk->nr_zones = ublk_get_nr_zones(ub);
+
+	return 0;
+}
+
+/* Based on virtblk_alloc_report_buffer */
+static void *ublk_alloc_report_buffer(struct ublk_device *ublk,
+				      unsigned int nr_zones, size_t *buflen)
+{
+	struct request_queue *q = ublk->ub_disk->queue;
+	size_t bufsize;
+	void *buf;
+
+	nr_zones = min_t(unsigned int, nr_zones,
+			 ublk->ub_disk->nr_zones);
+
+	bufsize = nr_zones * sizeof(struct blk_zone);
+	bufsize =
+		min_t(size_t, bufsize, queue_max_hw_sectors(q) << SECTOR_SHIFT);
+
+	while (bufsize >= sizeof(struct blk_zone)) {
+		buf = kvmalloc(bufsize, GFP_KERNEL | __GFP_NORETRY);
+		if (buf) {
+			*buflen = bufsize;
+			return buf;
+		}
+		bufsize >>= 1;
+	}
+
+	*buflen = 0;
+	return NULL;
+}
+
+static int ublk_report_zones(struct gendisk *disk, sector_t sector,
+		      unsigned int nr_zones, report_zones_cb cb, void *data)
+{
+	struct ublk_device *ub = disk->private_data;
+	unsigned int zone_size_sectors = disk->queue->limits.chunk_sectors;
+	unsigned int first_zone = sector >> ilog2(zone_size_sectors);
+	unsigned int done_zones = 0;
+	unsigned int max_zones_per_request;
+	int ret;
+	struct blk_zone *buffer;
+	size_t buffer_length;
+
+	nr_zones = min_t(unsigned int, ub->ub_disk->nr_zones - first_zone,
+			 nr_zones);
+
+	buffer = ublk_alloc_report_buffer(ub, nr_zones, &buffer_length);
+	if (!buffer)
+		return -ENOMEM;
+
+	max_zones_per_request = buffer_length / sizeof(struct blk_zone);
+
+	while (done_zones < nr_zones) {
+		unsigned int remaining_zones = nr_zones - done_zones;
+		unsigned int zones_in_request =
+			min_t(unsigned int, remaining_zones, max_zones_per_request);
+		struct request *req;
+		struct ublk_rq_data *pdu;
+		blk_status_t status;
+
+		memset(buffer, 0, buffer_length);
+
+		req = blk_mq_alloc_request(disk->queue, REQ_OP_DRV_IN, 0);
+		if (IS_ERR(req)) {
+			ret = PTR_ERR(req);
+			goto out;
+		}
+
+		pdu = blk_mq_rq_to_pdu(req);
+		pdu->operation = UBLK_IO_OP_REPORT_ZONES;
+		pdu->sector = sector;
+		pdu->nr_zones = zones_in_request;
+
+		ret = blk_rq_map_kern(disk->queue, req, buffer, buffer_length,
+					GFP_KERNEL);
+		if (ret) {
+			blk_mq_free_request(req);
+			goto out;
+		}
+
+		status = blk_execute_rq(req, 0);
+		ret = blk_status_to_errno(status);
+		blk_mq_free_request(req);
+		if (ret)
+			goto out;
+
+		for (unsigned int i = 0; i < zones_in_request; i++) {
+			struct blk_zone *zone = buffer + i;
+
+			/* A zero length zone means no more zones in this response */
+			if (!zone->len)
+				break;
+
+			ret = cb(zone, i, data);
+			if (ret)
+				goto out;
+
+			done_zones++;
+			sector += zone_size_sectors;
+
+		}
+	}
+
+	ret = done_zones;
+
+out:
+	kvfree(buffer);
+	return ret;
+}
+
+static blk_status_t ublk_setup_iod_zoned(struct ublk_queue *ubq,
+					 struct request *req)
+{
+	struct ublksrv_io_desc *iod = ublk_get_iod(ubq, req->tag);
+	struct ublk_io *io = &ubq->ios[req->tag];
+	struct ublk_rq_data *pdu = blk_mq_rq_to_pdu(req);
+	u32 ublk_op;
+
+	switch (req_op(req)) {
+	case REQ_OP_ZONE_OPEN:
+		ublk_op = UBLK_IO_OP_ZONE_OPEN;
+		break;
+	case REQ_OP_ZONE_CLOSE:
+		ublk_op = UBLK_IO_OP_ZONE_CLOSE;
+		break;
+	case REQ_OP_ZONE_FINISH:
+		ublk_op = UBLK_IO_OP_ZONE_FINISH;
+		break;
+	case REQ_OP_ZONE_RESET:
+		ublk_op = UBLK_IO_OP_ZONE_RESET;
+		break;
+	case REQ_OP_ZONE_APPEND:
+		ublk_op = UBLK_IO_OP_ZONE_APPEND;
+		break;
+	case REQ_OP_ZONE_RESET_ALL:
+		ublk_op = UBLK_IO_OP_ZONE_RESET_ALL;
+		break;
+	case REQ_OP_DRV_IN:
+		ublk_op = pdu->operation;
+		switch (ublk_op) {
+		case UBLK_IO_OP_REPORT_ZONES:
+			iod->op_flags = ublk_op | ublk_req_build_flags(req);
+			iod->nr_zones = pdu->nr_zones;
+			iod->start_sector = pdu->sector;
+			return BLK_STS_OK;
+		default:
+			return BLK_STS_IOERR;
+		}
+	case REQ_OP_DRV_OUT:
+		/* We do not support drv_out */
+		return BLK_STS_NOTSUPP;
+	default:
+		return BLK_STS_IOERR;
+	}
+
+	iod->op_flags = ublk_op | ublk_req_build_flags(req);
+	iod->nr_sectors = blk_rq_sectors(req);
+	iod->start_sector = blk_rq_pos(req);
+	iod->addr = io->addr;
+
+	return BLK_STS_OK;
+}
+
+#else
+
+#define ublk_report_zones (NULL)
+
+static int ublk_dev_param_zoned_validate(const struct ublk_device *ub)
+{
+	return -EOPNOTSUPP;
+}
+
+static int ublk_dev_param_zoned_apply(struct ublk_device *ub)
+{
+	return -EOPNOTSUPP;
+}
+
+static int ublk_revalidate_disk_zones(struct ublk_device *ub)
+{
+	return 0;
+}
+
+static blk_status_t ublk_setup_iod_zoned(struct ublk_queue *ubq,
+					 struct request *req)
+{
+	return BLK_STS_NOTSUPP;
+}
+
+#endif
+
+static inline void __ublk_complete_rq(struct request *req);
+static void ublk_complete_rq(struct kref *ref);
+
+static dev_t ublk_chr_devt;
+static const struct class ublk_chr_class = {
+	.name = "ublk-char",
+};
+
+static DEFINE_IDR(ublk_index_idr);
+static DEFINE_SPINLOCK(ublk_idr_lock);
+static wait_queue_head_t ublk_idr_wq;	/* wait until one idr is freed */
+
+static DEFINE_MUTEX(ublk_ctl_mutex);
+
+/*
+ * Max ublk devices allowed to add
+ *
+ * It can be extended to one per-user limit in future or even controlled
+ * by cgroup.
+ */
+static unsigned int ublks_max = 64;
+static unsigned int ublks_added;	/* protected by ublk_ctl_mutex */
+
+static struct miscdevice ublk_misc;
+
+static inline unsigned ublk_pos_to_hwq(loff_t pos)
+{
+	return ((pos - UBLKSRV_IO_BUF_OFFSET) >> UBLK_QID_OFF) &
+		UBLK_QID_BITS_MASK;
+}
+
+static inline unsigned ublk_pos_to_buf_off(loff_t pos)
+{
+	return (pos - UBLKSRV_IO_BUF_OFFSET) & UBLK_IO_BUF_BITS_MASK;
+}
+
+static inline unsigned ublk_pos_to_tag(loff_t pos)
+{
+	return ((pos - UBLKSRV_IO_BUF_OFFSET) >> UBLK_TAG_OFF) &
+		UBLK_TAG_BITS_MASK;
+}
+
+static void ublk_dev_param_basic_apply(struct ublk_device *ub)
+{
+	struct request_queue *q = ub->ub_disk->queue;
+	const struct ublk_param_basic *p = &ub->params.basic;
+
+	blk_queue_logical_block_size(q, 1 << p->logical_bs_shift);
+	blk_queue_physical_block_size(q, 1 << p->physical_bs_shift);
+	blk_queue_io_min(q, 1 << p->io_min_shift);
+	blk_queue_io_opt(q, 1 << p->io_opt_shift);
+
+	blk_queue_write_cache(q, p->attrs & UBLK_ATTR_VOLATILE_CACHE,
+			p->attrs & UBLK_ATTR_FUA);
+	if (p->attrs & UBLK_ATTR_ROTATIONAL)
+		blk_queue_flag_clear(QUEUE_FLAG_NONROT, q);
+	else
+		blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
+
+	blk_queue_max_hw_sectors(q, p->max_sectors);
+	blk_queue_chunk_sectors(q, p->chunk_sectors);
+	blk_queue_virt_boundary(q, p->virt_boundary_mask);
+
+	if (p->attrs & UBLK_ATTR_READ_ONLY)
+		set_disk_ro(ub->ub_disk, true);
+
+	set_capacity(ub->ub_disk, p->dev_sectors);
+}
+
+static void ublk_dev_param_discard_apply(struct ublk_device *ub)
+{
+	struct request_queue *q = ub->ub_disk->queue;
+	const struct ublk_param_discard *p = &ub->params.discard;
+
+	q->limits.discard_alignment = p->discard_alignment;
+	q->limits.discard_granularity = p->discard_granularity;
+	blk_queue_max_discard_sectors(q, p->max_discard_sectors);
+	blk_queue_max_write_zeroes_sectors(q,
+			p->max_write_zeroes_sectors);
+	blk_queue_max_discard_segments(q, p->max_discard_segments);
+}
+
+static int ublk_validate_params(const struct ublk_device *ub)
+{
+	/* basic param is the only one which must be set */
+	if (ub->params.types & UBLK_PARAM_TYPE_BASIC) {
+		const struct ublk_param_basic *p = &ub->params.basic;
+
+		if (p->logical_bs_shift > PAGE_SHIFT || p->logical_bs_shift < 9)
+			return -EINVAL;
+
+		if (p->logical_bs_shift > p->physical_bs_shift)
+			return -EINVAL;
+
+		if (p->max_sectors > (ub->dev_info.max_io_buf_bytes >> 9))
+			return -EINVAL;
+
+		if (ublk_dev_is_zoned(ub) && !p->chunk_sectors)
+			return -EINVAL;
+	} else
+		return -EINVAL;
+
+	if (ub->params.types & UBLK_PARAM_TYPE_DISCARD) {
+		const struct ublk_param_discard *p = &ub->params.discard;
+
+		/* So far, only support single segment discard */
+		if (p->max_discard_sectors && p->max_discard_segments != 1)
+			return -EINVAL;
+
+		if (!p->discard_granularity)
+			return -EINVAL;
+	}
+
+	/* dev_t is read-only */
+	if (ub->params.types & UBLK_PARAM_TYPE_DEVT)
+		return -EINVAL;
+
+	if (ub->params.types & UBLK_PARAM_TYPE_ZONED)
+		return ublk_dev_param_zoned_validate(ub);
+	else if (ublk_dev_is_zoned(ub))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int ublk_apply_params(struct ublk_device *ub)
+{
+	if (!(ub->params.types & UBLK_PARAM_TYPE_BASIC))
+		return -EINVAL;
+
+	ublk_dev_param_basic_apply(ub);
+
+	if (ub->params.types & UBLK_PARAM_TYPE_DISCARD)
+		ublk_dev_param_discard_apply(ub);
+
+	if (ub->params.types & UBLK_PARAM_TYPE_ZONED)
+		return ublk_dev_param_zoned_apply(ub);
+
+	return 0;
+}
+
+static inline bool ublk_support_user_copy(const struct ublk_queue *ubq)
+{
+	return ubq->flags & UBLK_F_USER_COPY;
+}
+
+static inline bool ublk_need_req_ref(const struct ublk_queue *ubq)
+{
+	/*
+	 * read()/write() is involved in user copy, so request reference
+	 * has to be grabbed
+	 */
+	return ublk_support_user_copy(ubq);
+}
+
+static inline void ublk_init_req_ref(const struct ublk_queue *ubq,
+		struct request *req)
+{
+	if (ublk_need_req_ref(ubq)) {
+		struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
+
+		kref_init(&data->ref);
+	}
+}
+
+static inline bool ublk_get_req_ref(const struct ublk_queue *ubq,
+		struct request *req)
+{
+	if (ublk_need_req_ref(ubq)) {
+		struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
+
+		return kref_get_unless_zero(&data->ref);
+	}
+
+	return true;
+}
+
+static inline void ublk_put_req_ref(const struct ublk_queue *ubq,
+		struct request *req)
+{
+	if (ublk_need_req_ref(ubq)) {
+		struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
+
+		kref_put(&data->ref, ublk_complete_rq);
+	} else {
+		__ublk_complete_rq(req);
+	}
+}
+
+static inline bool ublk_need_get_data(const struct ublk_queue *ubq)
+{
+	return ubq->flags & UBLK_F_NEED_GET_DATA;
+}
+
+static struct ublk_device *ublk_get_device(struct ublk_device *ub)
+{
+	if (kobject_get_unless_zero(&ub->cdev_dev.kobj))
+		return ub;
+	return NULL;
+}
+
+static void ublk_put_device(struct ublk_device *ub)
+{
+	put_device(&ub->cdev_dev);
+}
+
+static inline struct ublk_queue *ublk_get_queue(struct ublk_device *dev,
+		int qid)
+{
+       return (struct ublk_queue *)&(dev->__queues[qid * dev->queue_size]);
+}
+
+static inline bool ublk_rq_has_data(const struct request *rq)
+{
+	return bio_has_data(rq->bio);
+}
+
+static inline struct ublksrv_io_desc *ublk_get_iod(struct ublk_queue *ubq,
+		int tag)
+{
+	return (struct ublksrv_io_desc *)
+		&(ubq->io_cmd_buf[tag * sizeof(struct ublksrv_io_desc)]);
+}
+
+static inline char *ublk_queue_cmd_buf(struct ublk_device *ub, int q_id)
+{
+	return ublk_get_queue(ub, q_id)->io_cmd_buf;
+}
+
+static inline int ublk_queue_cmd_buf_size(struct ublk_device *ub, int q_id)
+{
+	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);
+
+	return round_up(ubq->q_depth * sizeof(struct ublksrv_io_desc),
+			PAGE_SIZE);
+}
+
+static inline bool ublk_queue_can_use_recovery_reissue(
+		struct ublk_queue *ubq)
+{
+	return (ubq->flags & UBLK_F_USER_RECOVERY) &&
+			(ubq->flags & UBLK_F_USER_RECOVERY_REISSUE);
+}
+
+static inline bool ublk_queue_can_use_recovery(
+		struct ublk_queue *ubq)
+{
+	return ubq->flags & UBLK_F_USER_RECOVERY;
+}
+
+static inline bool ublk_can_use_recovery(struct ublk_device *ub)
+{
+	return ub->dev_info.flags & UBLK_F_USER_RECOVERY;
+}
+
+static void ublk_free_disk(struct gendisk *disk)
+{
+	struct ublk_device *ub = disk->private_data;
+
+	clear_bit(UB_STATE_USED, &ub->state);
+	put_device(&ub->cdev_dev);
+}
+
+static void ublk_store_owner_uid_gid(unsigned int *owner_uid,
+		unsigned int *owner_gid)
+{
+	kuid_t uid;
+	kgid_t gid;
+
+	current_uid_gid(&uid, &gid);
+
+	*owner_uid = from_kuid(&init_user_ns, uid);
+	*owner_gid = from_kgid(&init_user_ns, gid);
+}
+
+static int ublk_open(struct gendisk *disk, blk_mode_t mode)
+{
+	struct ublk_device *ub = disk->private_data;
+
+	if (capable(CAP_SYS_ADMIN))
+		return 0;
+
+	/*
+	 * If it is one unprivileged device, only owner can open
+	 * the disk. Otherwise it could be one trap made by one
+	 * evil user who grants this disk's privileges to other
+	 * users deliberately.
+	 *
+	 * This way is reasonable too given anyone can create
+	 * unprivileged device, and no need other's grant.
+	 */
+	if (ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV) {
+		unsigned int curr_uid, curr_gid;
+
+		ublk_store_owner_uid_gid(&curr_uid, &curr_gid);
+
+		if (curr_uid != ub->dev_info.owner_uid || curr_gid !=
+				ub->dev_info.owner_gid)
+			return -EPERM;
+	}
+
+	return 0;
+}
+
+static const struct block_device_operations ub_fops = {
+	.owner =	THIS_MODULE,
+	.open =		ublk_open,
+	.free_disk =	ublk_free_disk,
+	.report_zones =	ublk_report_zones,
+};
+
+#define UBLK_MAX_PIN_PAGES	32
+
+struct ublk_io_iter {
+	struct page *pages[UBLK_MAX_PIN_PAGES];
+	struct bio *bio;
+	struct bvec_iter iter;
+};
+
+/* return how many pages are copied */
+static void ublk_copy_io_pages(struct ublk_io_iter *data,
+		size_t total, size_t pg_off, int dir)
+{
+	unsigned done = 0;
+	unsigned pg_idx = 0;
+
+	while (done < total) {
+		struct bio_vec bv = bio_iter_iovec(data->bio, data->iter);
+		unsigned int bytes = min3(bv.bv_len, (unsigned)total - done,
+				(unsigned)(PAGE_SIZE - pg_off));
+		void *bv_buf = bvec_kmap_local(&bv);
+		void *pg_buf = kmap_local_page(data->pages[pg_idx]);
+
+		if (dir == ITER_DEST)
+			memcpy(pg_buf + pg_off, bv_buf, bytes);
+		else
+			memcpy(bv_buf, pg_buf + pg_off, bytes);
+
+		kunmap_local(pg_buf);
+		kunmap_local(bv_buf);
+
+		/* advance page array */
+		pg_off += bytes;
+		if (pg_off == PAGE_SIZE) {
+			pg_idx += 1;
+			pg_off = 0;
+		}
+
+		done += bytes;
+
+		/* advance bio */
+		bio_advance_iter_single(data->bio, &data->iter, bytes);
+		if (!data->iter.bi_size) {
+			data->bio = data->bio->bi_next;
+			if (data->bio == NULL)
+				break;
+			data->iter = data->bio->bi_iter;
+		}
+	}
+}
+
+static bool ublk_advance_io_iter(const struct request *req,
+		struct ublk_io_iter *iter, unsigned int offset)
+{
+	struct bio *bio = req->bio;
+
+	for_each_bio(bio) {
+		if (bio->bi_iter.bi_size > offset) {
+			iter->bio = bio;
+			iter->iter = bio->bi_iter;
+			bio_advance_iter(iter->bio, &iter->iter, offset);
+			return true;
+		}
+		offset -= bio->bi_iter.bi_size;
+	}
+	return false;
+}
+
+/*
+ * Copy data between request pages and io_iter, and 'offset'
+ * is the start point of linear offset of request.
+ */
+static size_t ublk_copy_user_pages(const struct request *req,
+		unsigned offset, struct iov_iter *uiter, int dir)
+{
+	struct ublk_io_iter iter;
+	size_t done = 0;
+
+	if (!ublk_advance_io_iter(req, &iter, offset))
+		return 0;
+
+	while (iov_iter_count(uiter) && iter.bio) {
+		unsigned nr_pages;
+		ssize_t len;
+		size_t off;
+		int i;
+
+		len = iov_iter_get_pages2(uiter, iter.pages,
+				iov_iter_count(uiter),
+				UBLK_MAX_PIN_PAGES, &off);
+		if (len <= 0)
+			return done;
+
+		ublk_copy_io_pages(&iter, len, off, dir);
+		nr_pages = DIV_ROUND_UP(len + off, PAGE_SIZE);
+		for (i = 0; i < nr_pages; i++) {
+			if (dir == ITER_DEST)
+				set_page_dirty(iter.pages[i]);
+			put_page(iter.pages[i]);
+		}
+		done += len;
+	}
+
+	return done;
+}
+
+static inline bool ublk_need_map_req(const struct request *req)
+{
+	return ublk_rq_has_data(req) && req_op(req) == REQ_OP_WRITE;
+}
+
+static inline bool ublk_need_unmap_req(const struct request *req)
+{
+	return ublk_rq_has_data(req) &&
+	       (req_op(req) == REQ_OP_READ || req_op(req) == REQ_OP_DRV_IN);
+}
+
+static int ublk_map_io(const struct ublk_queue *ubq, const struct request *req,
+		struct ublk_io *io)
+{
+	const unsigned int rq_bytes = blk_rq_bytes(req);
+
+	if (ublk_support_user_copy(ubq))
+		return rq_bytes;
+
+	/*
+	 * no zero copy, we delay copy WRITE request data into ublksrv
+	 * context and the big benefit is that pinning pages in current
+	 * context is pretty fast, see ublk_pin_user_pages
+	 */
+	if (ublk_need_map_req(req)) {
+		struct iov_iter iter;
+		struct iovec iov;
+		const int dir = ITER_DEST;
+
+		import_single_range(dir, u64_to_user_ptr(io->addr), rq_bytes,
+				&iov, &iter);
+
+		return ublk_copy_user_pages(req, 0, &iter, dir);
+	}
+	return rq_bytes;
+}
+
+static int ublk_unmap_io(const struct ublk_queue *ubq,
+		const struct request *req,
+		struct ublk_io *io)
+{
+	const unsigned int rq_bytes = blk_rq_bytes(req);
+
+	if (ublk_support_user_copy(ubq))
+		return rq_bytes;
+
+	if (ublk_need_unmap_req(req)) {
+		struct iov_iter iter;
+		struct iovec iov;
+		const int dir = ITER_SOURCE;
+
+		WARN_ON_ONCE(io->res > rq_bytes);
+
+		import_single_range(dir, u64_to_user_ptr(io->addr), io->res,
+				&iov, &iter);
+		return ublk_copy_user_pages(req, 0, &iter, dir);
+	}
+	return rq_bytes;
+}
+
+static inline unsigned int ublk_req_build_flags(struct request *req)
+{
+	unsigned flags = 0;
+
+	if (req->cmd_flags & REQ_FAILFAST_DEV)
+		flags |= UBLK_IO_F_FAILFAST_DEV;
+
+	if (req->cmd_flags & REQ_FAILFAST_TRANSPORT)
+		flags |= UBLK_IO_F_FAILFAST_TRANSPORT;
+
+	if (req->cmd_flags & REQ_FAILFAST_DRIVER)
+		flags |= UBLK_IO_F_FAILFAST_DRIVER;
+
+	if (req->cmd_flags & REQ_META)
+		flags |= UBLK_IO_F_META;
+
+	if (req->cmd_flags & REQ_FUA)
+		flags |= UBLK_IO_F_FUA;
+
+	if (req->cmd_flags & REQ_NOUNMAP)
+		flags |= UBLK_IO_F_NOUNMAP;
+
+	if (req->cmd_flags & REQ_SWAP)
+		flags |= UBLK_IO_F_SWAP;
+
+	return flags;
+}
+
+static blk_status_t ublk_setup_iod(struct ublk_queue *ubq, struct request *req)
+{
+	struct ublksrv_io_desc *iod = ublk_get_iod(ubq, req->tag);
+	struct ublk_io *io = &ubq->ios[req->tag];
+	enum req_op op = req_op(req);
+	u32 ublk_op;
+
+	if (!ublk_queue_is_zoned(ubq) &&
+	    (op_is_zone_mgmt(op) || op == REQ_OP_ZONE_APPEND))
+		return BLK_STS_IOERR;
+
+	switch (req_op(req)) {
+	case REQ_OP_READ:
+		ublk_op = UBLK_IO_OP_READ;
+		break;
+	case REQ_OP_WRITE:
+		ublk_op = UBLK_IO_OP_WRITE;
+		break;
+	case REQ_OP_FLUSH:
+		ublk_op = UBLK_IO_OP_FLUSH;
+		break;
+	case REQ_OP_DISCARD:
+		ublk_op = UBLK_IO_OP_DISCARD;
+		break;
+	case REQ_OP_WRITE_ZEROES:
+		ublk_op = UBLK_IO_OP_WRITE_ZEROES;
+		break;
+	default:
+		if (ublk_queue_is_zoned(ubq))
+			return ublk_setup_iod_zoned(ubq, req);
+		return BLK_STS_IOERR;
+	}
+
+	/* need to translate since kernel may change */
+	iod->op_flags = ublk_op | ublk_req_build_flags(req);
+	iod->nr_sectors = blk_rq_sectors(req);
+	iod->start_sector = blk_rq_pos(req);
+	iod->addr = io->addr;
+
+	return BLK_STS_OK;
+}
+
+static inline struct ublk_uring_cmd_pdu *ublk_get_uring_cmd_pdu(
+		struct io_uring_cmd *ioucmd)
+{
+	return (struct ublk_uring_cmd_pdu *)&ioucmd->pdu;
+}
+
+static inline bool ubq_daemon_is_dying(struct ublk_queue *ubq)
+{
+	return ubq->ubq_daemon->flags & PF_EXITING;
+}
+
+/* todo: handle partial completion */
+static inline void __ublk_complete_rq(struct request *req)
+{
+	struct ublk_queue *ubq = req->mq_hctx->driver_data;
+	struct ublk_io *io = &ubq->ios[req->tag];
+	unsigned int unmapped_bytes;
+	blk_status_t res = BLK_STS_OK;
+
+	/* called from ublk_abort_queue() code path */
+	if (io->flags & UBLK_IO_FLAG_ABORTED) {
+		res = BLK_STS_IOERR;
+		goto exit;
+	}
+
+	/* failed read IO if nothing is read */
+	if (!io->res && req_op(req) == REQ_OP_READ)
+		io->res = -EIO;
+
+	if (io->res < 0) {
+		res = errno_to_blk_status(io->res);
+		goto exit;
+	}
+
+	/*
+	 * FLUSH, DISCARD or WRITE_ZEROES usually won't return bytes returned, so end them
+	 * directly.
+	 *
+	 * Both the two needn't unmap.
+	 */
+	if (req_op(req) != REQ_OP_READ && req_op(req) != REQ_OP_WRITE &&
+	    req_op(req) != REQ_OP_DRV_IN)
+		goto exit;
+
+	/* for READ request, writing data in iod->addr to rq buffers */
+	unmapped_bytes = ublk_unmap_io(ubq, req, io);
+
+	/*
+	 * Extremely impossible since we got data filled in just before
+	 *
+	 * Re-read simply for this unlikely case.
+	 */
+	if (unlikely(unmapped_bytes < io->res))
+		io->res = unmapped_bytes;
+
+	if (blk_update_request(req, BLK_STS_OK, io->res))
+		blk_mq_requeue_request(req, true);
+	else
+		__blk_mq_end_request(req, BLK_STS_OK);
+
+	return;
+exit:
+	blk_mq_end_request(req, res);
+}
+
+static void ublk_complete_rq(struct kref *ref)
+{
+	struct ublk_rq_data *data = container_of(ref, struct ublk_rq_data,
+			ref);
+	struct request *req = blk_mq_rq_from_pdu(data);
+
+	__ublk_complete_rq(req);
+}
+
+/*
+ * Since __ublk_rq_task_work always fails requests immediately during
+ * exiting, __ublk_fail_req() is only called from abort context during
+ * exiting. So lock is unnecessary.
+ *
+ * Also aborting may not be started yet, keep in mind that one failed
+ * request may be issued by block layer again.
+ */
+static void __ublk_fail_req(struct ublk_queue *ubq, struct ublk_io *io,
+		struct request *req)
+{
+	WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_ACTIVE);
+
+	if (!(io->flags & UBLK_IO_FLAG_ABORTED)) {
+		io->flags |= UBLK_IO_FLAG_ABORTED;
+		if (ublk_queue_can_use_recovery_reissue(ubq))
+			blk_mq_requeue_request(req, false);
+		else
+			ublk_put_req_ref(ubq, req);
+	}
+}
+
+static void ubq_complete_io_cmd(struct ublk_io *io, int res,
+				unsigned issue_flags)
+{
+	/* mark this cmd owned by ublksrv */
+	io->flags |= UBLK_IO_FLAG_OWNED_BY_SRV;
+
+	/*
+	 * clear ACTIVE since we are done with this sqe/cmd slot
+	 * We can only accept io cmd in case of being not active.
+	 */
+	io->flags &= ~UBLK_IO_FLAG_ACTIVE;
+
+	/* tell ublksrv one io request is coming */
+	io_uring_cmd_done(io->cmd, res, 0, issue_flags);
+}
+
+#define UBLK_REQUEUE_DELAY_MS	3
+
+static inline void __ublk_abort_rq(struct ublk_queue *ubq,
+		struct request *rq)
+{
+	/* We cannot process this rq so just requeue it. */
+	if (ublk_queue_can_use_recovery(ubq))
+		blk_mq_requeue_request(rq, false);
+	else
+		blk_mq_end_request(rq, BLK_STS_IOERR);
+
+	mod_delayed_work(system_wq, &ubq->dev->monitor_work, 0);
+}
+
+static inline void __ublk_rq_task_work(struct request *req,
+				       unsigned issue_flags)
+{
+	struct ublk_queue *ubq = req->mq_hctx->driver_data;
+	int tag = req->tag;
+	struct ublk_io *io = &ubq->ios[tag];
+	unsigned int mapped_bytes;
+
+	pr_devel("%s: complete: op %d, qid %d tag %d io_flags %x addr %llx\n",
+			__func__, io->cmd->cmd_op, ubq->q_id, req->tag, io->flags,
+			ublk_get_iod(ubq, req->tag)->addr);
+
+	/*
+	 * Task is exiting if either:
+	 *
+	 * (1) current != ubq_daemon.
+	 * io_uring_cmd_complete_in_task() tries to run task_work
+	 * in a workqueue if ubq_daemon(cmd's task) is PF_EXITING.
+	 *
+	 * (2) current->flags & PF_EXITING.
+	 */
+	if (unlikely(current != ubq->ubq_daemon || current->flags & PF_EXITING)) {
+		__ublk_abort_rq(ubq, req);
+		return;
+	}
+
+	if (ublk_need_get_data(ubq) && ublk_need_map_req(req)) {
+		/*
+		 * We have not handled UBLK_IO_NEED_GET_DATA command yet,
+		 * so immepdately pass UBLK_IO_RES_NEED_GET_DATA to ublksrv
+		 * and notify it.
+		 */
+		if (!(io->flags & UBLK_IO_FLAG_NEED_GET_DATA)) {
+			io->flags |= UBLK_IO_FLAG_NEED_GET_DATA;
+			pr_devel("%s: need get data. op %d, qid %d tag %d io_flags %x\n",
+					__func__, io->cmd->cmd_op, ubq->q_id,
+					req->tag, io->flags);
+			ubq_complete_io_cmd(io, UBLK_IO_RES_NEED_GET_DATA, issue_flags);
+			return;
+		}
+		/*
+		 * We have handled UBLK_IO_NEED_GET_DATA command,
+		 * so clear UBLK_IO_FLAG_NEED_GET_DATA now and just
+		 * do the copy work.
+		 */
+		io->flags &= ~UBLK_IO_FLAG_NEED_GET_DATA;
+		/* update iod->addr because ublksrv may have passed a new io buffer */
+		ublk_get_iod(ubq, req->tag)->addr = io->addr;
+		pr_devel("%s: update iod->addr: op %d, qid %d tag %d io_flags %x addr %llx\n",
+				__func__, io->cmd->cmd_op, ubq->q_id, req->tag, io->flags,
+				ublk_get_iod(ubq, req->tag)->addr);
+	}
+
+	mapped_bytes = ublk_map_io(ubq, req, io);
+
+	/* partially mapped, update io descriptor */
+	if (unlikely(mapped_bytes != blk_rq_bytes(req))) {
+		/*
+		 * Nothing mapped, retry until we succeed.
+		 *
+		 * We may never succeed in mapping any bytes here because
+		 * of OOM. TODO: reserve one buffer with single page pinned
+		 * for providing forward progress guarantee.
+		 */
+		if (unlikely(!mapped_bytes)) {
+			blk_mq_requeue_request(req, false);
+			blk_mq_delay_kick_requeue_list(req->q,
+					UBLK_REQUEUE_DELAY_MS);
+			return;
+		}
+
+		ublk_get_iod(ubq, req->tag)->nr_sectors =
+			mapped_bytes >> 9;
+	}
+
+	ublk_init_req_ref(ubq, req);
+	ubq_complete_io_cmd(io, UBLK_IO_RES_OK, issue_flags);
+}
+
+static inline void ublk_forward_io_cmds(struct ublk_queue *ubq,
+					unsigned issue_flags)
+{
+	struct llist_node *io_cmds = llist_del_all(&ubq->io_cmds);
+	struct ublk_rq_data *data, *tmp;
+
+	io_cmds = llist_reverse_order(io_cmds);
+	llist_for_each_entry_safe(data, tmp, io_cmds, node)
+		__ublk_rq_task_work(blk_mq_rq_from_pdu(data), issue_flags);
+}
+
+static inline void ublk_abort_io_cmds(struct ublk_queue *ubq)
+{
+	struct llist_node *io_cmds = llist_del_all(&ubq->io_cmds);
+	struct ublk_rq_data *data, *tmp;
+
+	llist_for_each_entry_safe(data, tmp, io_cmds, node)
+		__ublk_abort_rq(ubq, blk_mq_rq_from_pdu(data));
+}
+
+static void ublk_rq_task_work_cb(struct io_uring_cmd *cmd, unsigned issue_flags)
+{
+	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
+	struct ublk_queue *ubq = pdu->ubq;
+
+	ublk_forward_io_cmds(ubq, issue_flags);
+}
+
+static void ublk_queue_cmd(struct ublk_queue *ubq, struct request *rq)
+{
+	struct ublk_rq_data *data = blk_mq_rq_to_pdu(rq);
+	struct ublk_io *io;
+
+	if (!llist_add(&data->node, &ubq->io_cmds))
+		return;
+
+	io = &ubq->ios[rq->tag];
+	/*
+	 * If the check pass, we know that this is a re-issued request aborted
+	 * previously in monitor_work because the ubq_daemon(cmd's task) is
+	 * PF_EXITING. We cannot call io_uring_cmd_complete_in_task() anymore
+	 * because this ioucmd's io_uring context may be freed now if no inflight
+	 * ioucmd exists. Otherwise we may cause null-deref in ctx->fallback_work.
+	 *
+	 * Note: monitor_work sets UBLK_IO_FLAG_ABORTED and ends this request(releasing
+	 * the tag). Then the request is re-started(allocating the tag) and we are here.
+	 * Since releasing/allocating a tag implies smp_mb(), finding UBLK_IO_FLAG_ABORTED
+	 * guarantees that here is a re-issued request aborted previously.
+	 */
+	if (unlikely(io->flags & UBLK_IO_FLAG_ABORTED)) {
+		ublk_abort_io_cmds(ubq);
+	} else {
+		struct io_uring_cmd *cmd = io->cmd;
+		struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
+
+		pdu->ubq = ubq;
+		io_uring_cmd_complete_in_task(cmd, ublk_rq_task_work_cb);
+	}
+}
+
+static enum blk_eh_timer_return ublk_timeout(struct request *rq)
+{
+	struct ublk_queue *ubq = rq->mq_hctx->driver_data;
+
+	if (ubq->flags & UBLK_F_UNPRIVILEGED_DEV) {
+		if (!ubq->timeout) {
+			send_sig(SIGKILL, ubq->ubq_daemon, 0);
+			ubq->timeout = true;
+		}
+
+		return BLK_EH_DONE;
+	}
+
+	return BLK_EH_RESET_TIMER;
+}
+
+static blk_status_t ublk_queue_rq(struct blk_mq_hw_ctx *hctx,
+		const struct blk_mq_queue_data *bd)
+{
+	struct ublk_queue *ubq = hctx->driver_data;
+	struct request *rq = bd->rq;
+	blk_status_t res;
+
+	/* fill iod to slot in io cmd buffer */
+	res = ublk_setup_iod(ubq, rq);
+	if (unlikely(res != BLK_STS_OK))
+		return BLK_STS_IOERR;
+
+	/* With recovery feature enabled, force_abort is set in
+	 * ublk_stop_dev() before calling del_gendisk(). We have to
+	 * abort all requeued and new rqs here to let del_gendisk()
+	 * move on. Besides, we cannot not call io_uring_cmd_complete_in_task()
+	 * to avoid UAF on io_uring ctx.
+	 *
+	 * Note: force_abort is guaranteed to be seen because it is set
+	 * before request queue is unqiuesced.
+	 */
+	if (ublk_queue_can_use_recovery(ubq) && unlikely(ubq->force_abort))
+		return BLK_STS_IOERR;
+
+	blk_mq_start_request(bd->rq);
+
+	if (unlikely(ubq_daemon_is_dying(ubq))) {
+		__ublk_abort_rq(ubq, rq);
+		return BLK_STS_OK;
+	}
+
+	ublk_queue_cmd(ubq, rq);
+
+	return BLK_STS_OK;
+}
+
+static int ublk_init_hctx(struct blk_mq_hw_ctx *hctx, void *driver_data,
+		unsigned int hctx_idx)
+{
+	struct ublk_device *ub = driver_data;
+	struct ublk_queue *ubq = ublk_get_queue(ub, hctx->queue_num);
+
+	hctx->driver_data = ubq;
+	return 0;
+}
+
+static const struct blk_mq_ops ublk_mq_ops = {
+	.queue_rq       = ublk_queue_rq,
+	.init_hctx	= ublk_init_hctx,
+	.timeout	= ublk_timeout,
+};
+
+static int ublk_ch_open(struct inode *inode, struct file *filp)
+{
+	struct ublk_device *ub = container_of(inode->i_cdev,
+			struct ublk_device, cdev);
+
+	if (test_and_set_bit(UB_STATE_OPEN, &ub->state))
+		return -EBUSY;
+	filp->private_data = ub;
+	return 0;
+}
+
+static int ublk_ch_release(struct inode *inode, struct file *filp)
+{
+	struct ublk_device *ub = filp->private_data;
+
+	clear_bit(UB_STATE_OPEN, &ub->state);
+	return 0;
+}
+
+/* map pre-allocated per-queue cmd buffer to ublksrv daemon */
+static int ublk_ch_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	struct ublk_device *ub = filp->private_data;
+	size_t sz = vma->vm_end - vma->vm_start;
+	unsigned max_sz = UBLK_MAX_QUEUE_DEPTH * sizeof(struct ublksrv_io_desc);
+	unsigned long pfn, end, phys_off = vma->vm_pgoff << PAGE_SHIFT;
+	int q_id, ret = 0;
+
+	spin_lock(&ub->mm_lock);
+	if (!ub->mm)
+		ub->mm = current->mm;
+	if (current->mm != ub->mm)
+		ret = -EINVAL;
+	spin_unlock(&ub->mm_lock);
+
+	if (ret)
+		return ret;
+
+	if (vma->vm_flags & VM_WRITE)
+		return -EPERM;
+
+	end = UBLKSRV_CMD_BUF_OFFSET + ub->dev_info.nr_hw_queues * max_sz;
+	if (phys_off < UBLKSRV_CMD_BUF_OFFSET || phys_off >= end)
+		return -EINVAL;
+
+	q_id = (phys_off - UBLKSRV_CMD_BUF_OFFSET) / max_sz;
+	pr_devel("%s: qid %d, pid %d, addr %lx pg_off %lx sz %lu\n",
+			__func__, q_id, current->pid, vma->vm_start,
+			phys_off, (unsigned long)sz);
+
+	if (sz != ublk_queue_cmd_buf_size(ub, q_id))
+		return -EINVAL;
+
+	pfn = virt_to_phys(ublk_queue_cmd_buf(ub, q_id)) >> PAGE_SHIFT;
+	return remap_pfn_range(vma, vma->vm_start, pfn, sz, vma->vm_page_prot);
+}
+
+static void ublk_commit_completion(struct ublk_device *ub,
+		const struct ublksrv_io_cmd *ub_cmd)
+{
+	u32 qid = ub_cmd->q_id, tag = ub_cmd->tag;
+	struct ublk_queue *ubq = ublk_get_queue(ub, qid);
+	struct ublk_io *io = &ubq->ios[tag];
+	struct request *req;
+
+	/* now this cmd slot is owned by nbd driver */
+	io->flags &= ~UBLK_IO_FLAG_OWNED_BY_SRV;
+	io->res = ub_cmd->result;
+
+	/* find the io request and complete */
+	req = blk_mq_tag_to_rq(ub->tag_set.tags[qid], tag);
+	if (WARN_ON_ONCE(unlikely(!req)))
+		return;
+
+	if (req_op(req) == REQ_OP_ZONE_APPEND)
+		req->__sector = ub_cmd->zone_append_lba;
+
+	if (likely(!blk_should_fake_timeout(req->q)))
+		ublk_put_req_ref(ubq, req);
+}
+
+/*
+ * When ->ubq_daemon is exiting, either new request is ended immediately,
+ * or any queued io command is drained, so it is safe to abort queue
+ * lockless
+ */
+static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq)
+{
+	int i;
+
+	if (!ublk_get_device(ub))
+		return;
+
+	for (i = 0; i < ubq->q_depth; i++) {
+		struct ublk_io *io = &ubq->ios[i];
+
+		if (!(io->flags & UBLK_IO_FLAG_ACTIVE)) {
+			struct request *rq;
+
+			/*
+			 * Either we fail the request or ublk_rq_task_work_fn
+			 * will do it
+			 */
+			rq = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], i);
+			if (rq)
+				__ublk_fail_req(ubq, io, rq);
+		}
+	}
+	ublk_put_device(ub);
+}
+
+static void ublk_daemon_monitor_work(struct work_struct *work)
+{
+	struct ublk_device *ub =
+		container_of(work, struct ublk_device, monitor_work.work);
+	int i;
+
+	for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
+		struct ublk_queue *ubq = ublk_get_queue(ub, i);
+
+		if (ubq_daemon_is_dying(ubq)) {
+			if (ublk_queue_can_use_recovery(ubq))
+				schedule_work(&ub->quiesce_work);
+			else
+				schedule_work(&ub->stop_work);
+
+			/* abort queue is for making forward progress */
+			ublk_abort_queue(ub, ubq);
+		}
+	}
+
+	/*
+	 * We can't schedule monitor work after ub's state is not UBLK_S_DEV_LIVE.
+	 * after ublk_remove() or __ublk_quiesce_dev() is started.
+	 *
+	 * No need ub->mutex, monitor work are canceled after state is marked
+	 * as not LIVE, so new state is observed reliably.
+	 */
+	if (ub->dev_info.state == UBLK_S_DEV_LIVE)
+		schedule_delayed_work(&ub->monitor_work,
+				UBLK_DAEMON_MONITOR_PERIOD);
+}
+
+static inline bool ublk_queue_ready(struct ublk_queue *ubq)
+{
+	return ubq->nr_io_ready == ubq->q_depth;
+}
+
+static void ublk_cmd_cancel_cb(struct io_uring_cmd *cmd, unsigned issue_flags)
+{
+	io_uring_cmd_done(cmd, UBLK_IO_RES_ABORT, 0, issue_flags);
+}
+
+static void ublk_cancel_queue(struct ublk_queue *ubq)
+{
+	int i;
+
+	if (!ublk_queue_ready(ubq))
+		return;
+
+	for (i = 0; i < ubq->q_depth; i++) {
+		struct ublk_io *io = &ubq->ios[i];
+
+		if (io->flags & UBLK_IO_FLAG_ACTIVE)
+			io_uring_cmd_complete_in_task(io->cmd,
+						      ublk_cmd_cancel_cb);
+	}
+
+	/* all io commands are canceled */
+	ubq->nr_io_ready = 0;
+}
+
+/* Cancel all pending commands, must be called after del_gendisk() returns */
+static void ublk_cancel_dev(struct ublk_device *ub)
+{
+	int i;
+
+	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
+		ublk_cancel_queue(ublk_get_queue(ub, i));
+}
+
+static bool ublk_check_inflight_rq(struct request *rq, void *data)
+{
+	bool *idle = data;
+
+	if (blk_mq_request_started(rq)) {
+		*idle = false;
+		return false;
+	}
+	return true;
+}
+
+static void ublk_wait_tagset_rqs_idle(struct ublk_device *ub)
+{
+	bool idle;
+
+	WARN_ON_ONCE(!blk_queue_quiesced(ub->ub_disk->queue));
+	while (true) {
+		idle = true;
+		blk_mq_tagset_busy_iter(&ub->tag_set,
+				ublk_check_inflight_rq, &idle);
+		if (idle)
+			break;
+		msleep(UBLK_REQUEUE_DELAY_MS);
+	}
+}
+
+static void __ublk_quiesce_dev(struct ublk_device *ub)
+{
+	pr_devel("%s: quiesce ub: dev_id %d state %s\n",
+			__func__, ub->dev_info.dev_id,
+			ub->dev_info.state == UBLK_S_DEV_LIVE ?
+			"LIVE" : "QUIESCED");
+	blk_mq_quiesce_queue(ub->ub_disk->queue);
+	ublk_wait_tagset_rqs_idle(ub);
+	ub->dev_info.state = UBLK_S_DEV_QUIESCED;
+	ublk_cancel_dev(ub);
+	/* we are going to release task_struct of ubq_daemon and resets
+	 * ->ubq_daemon to NULL. So in monitor_work, check on ubq_daemon causes UAF.
+	 * Besides, monitor_work is not necessary in QUIESCED state since we have
+	 * already scheduled quiesce_work and quiesced all ubqs.
+	 *
+	 * Do not let monitor_work schedule itself if state it QUIESCED. And we cancel
+	 * it here and re-schedule it in END_USER_RECOVERY to avoid UAF.
+	 */
+	cancel_delayed_work_sync(&ub->monitor_work);
+}
+
+static void ublk_quiesce_work_fn(struct work_struct *work)
+{
+	struct ublk_device *ub =
+		container_of(work, struct ublk_device, quiesce_work);
+
+	mutex_lock(&ub->mutex);
+	if (ub->dev_info.state != UBLK_S_DEV_LIVE)
+		goto unlock;
+	__ublk_quiesce_dev(ub);
+ unlock:
+	mutex_unlock(&ub->mutex);
+}
+
+static void ublk_unquiesce_dev(struct ublk_device *ub)
+{
+	int i;
+
+	pr_devel("%s: unquiesce ub: dev_id %d state %s\n",
+			__func__, ub->dev_info.dev_id,
+			ub->dev_info.state == UBLK_S_DEV_LIVE ?
+			"LIVE" : "QUIESCED");
+	/* quiesce_work has run. We let requeued rqs be aborted
+	 * before running fallback_wq. "force_abort" must be seen
+	 * after request queue is unqiuesced. Then del_gendisk()
+	 * can move on.
+	 */
+	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
+		ublk_get_queue(ub, i)->force_abort = true;
+
+	blk_mq_unquiesce_queue(ub->ub_disk->queue);
+	/* We may have requeued some rqs in ublk_quiesce_queue() */
+	blk_mq_kick_requeue_list(ub->ub_disk->queue);
+}
+
+static void ublk_stop_dev(struct ublk_device *ub)
+{
+	mutex_lock(&ub->mutex);
+	if (ub->dev_info.state == UBLK_S_DEV_DEAD)
+		goto unlock;
+	if (ublk_can_use_recovery(ub)) {
+		if (ub->dev_info.state == UBLK_S_DEV_LIVE)
+			__ublk_quiesce_dev(ub);
+		ublk_unquiesce_dev(ub);
+	}
+	del_gendisk(ub->ub_disk);
+	ub->dev_info.state = UBLK_S_DEV_DEAD;
+	ub->dev_info.ublksrv_pid = -1;
+	put_disk(ub->ub_disk);
+	ub->ub_disk = NULL;
+ unlock:
+	ublk_cancel_dev(ub);
+	mutex_unlock(&ub->mutex);
+	cancel_delayed_work_sync(&ub->monitor_work);
+}
+
+/* device can only be started after all IOs are ready */
+static void ublk_mark_io_ready(struct ublk_device *ub, struct ublk_queue *ubq)
+{
+	mutex_lock(&ub->mutex);
+	ubq->nr_io_ready++;
+	if (ublk_queue_ready(ubq)) {
+		ubq->ubq_daemon = current;
+		get_task_struct(ubq->ubq_daemon);
+		ub->nr_queues_ready++;
+
+		if (capable(CAP_SYS_ADMIN))
+			ub->nr_privileged_daemon++;
+	}
+	if (ub->nr_queues_ready == ub->dev_info.nr_hw_queues)
+		complete_all(&ub->completion);
+	mutex_unlock(&ub->mutex);
+}
+
+static void ublk_handle_need_get_data(struct ublk_device *ub, int q_id,
+		int tag)
+{
+	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);
+	struct request *req = blk_mq_tag_to_rq(ub->tag_set.tags[q_id], tag);
+
+	ublk_queue_cmd(ubq, req);
+}
+
+static inline int ublk_check_cmd_op(u32 cmd_op)
+{
+	u32 ioc_type = _IOC_TYPE(cmd_op);
+
+	if (!IS_ENABLED(CONFIG_BLKDEV_UBLK_LEGACY_OPCODES) && ioc_type != 'u')
+		return -EOPNOTSUPP;
+
+	if (ioc_type != 'u' && ioc_type != 0)
+		return -EOPNOTSUPP;
+
+	return 0;
+}
+
+static inline void ublk_fill_io_cmd(struct ublk_io *io,
+		struct io_uring_cmd *cmd, unsigned long buf_addr)
+{
+	io->cmd = cmd;
+	io->flags |= UBLK_IO_FLAG_ACTIVE;
+	io->addr = buf_addr;
+}
+
+static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
+			       unsigned int issue_flags,
+			       const struct ublksrv_io_cmd *ub_cmd)
+{
+	struct ublk_device *ub = cmd->file->private_data;
+	struct ublk_queue *ubq;
+	struct ublk_io *io;
+	u32 cmd_op = cmd->cmd_op;
+	unsigned tag = ub_cmd->tag;
+	int ret = -EINVAL;
+	struct request *req;
+
+	pr_devel("%s: received: cmd op %d queue %d tag %d result %d\n",
+			__func__, cmd->cmd_op, ub_cmd->q_id, tag,
+			ub_cmd->result);
+
+	if (ub_cmd->q_id >= ub->dev_info.nr_hw_queues)
+		goto out;
+
+	ubq = ublk_get_queue(ub, ub_cmd->q_id);
+	if (!ubq || ub_cmd->q_id != ubq->q_id)
+		goto out;
+
+	if (ubq->ubq_daemon && ubq->ubq_daemon != current)
+		goto out;
+
+	if (tag >= ubq->q_depth)
+		goto out;
+
+	io = &ubq->ios[tag];
+
+	/* there is pending io cmd, something must be wrong */
+	if (io->flags & UBLK_IO_FLAG_ACTIVE) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	/*
+	 * ensure that the user issues UBLK_IO_NEED_GET_DATA
+	 * iff the driver have set the UBLK_IO_FLAG_NEED_GET_DATA.
+	 */
+	if ((!!(io->flags & UBLK_IO_FLAG_NEED_GET_DATA))
+			^ (_IOC_NR(cmd_op) == UBLK_IO_NEED_GET_DATA))
+		goto out;
+
+	ret = ublk_check_cmd_op(cmd_op);
+	if (ret)
+		goto out;
+
+	ret = -EINVAL;
+	switch (_IOC_NR(cmd_op)) {
+	case UBLK_IO_FETCH_REQ:
+		/* UBLK_IO_FETCH_REQ is only allowed before queue is setup */
+		if (ublk_queue_ready(ubq)) {
+			ret = -EBUSY;
+			goto out;
+		}
+		/*
+		 * The io is being handled by server, so COMMIT_RQ is expected
+		 * instead of FETCH_REQ
+		 */
+		if (io->flags & UBLK_IO_FLAG_OWNED_BY_SRV)
+			goto out;
+
+		if (!ublk_support_user_copy(ubq)) {
+			/*
+			 * FETCH_RQ has to provide IO buffer if NEED GET
+			 * DATA is not enabled
+			 */
+			if (!ub_cmd->addr && !ublk_need_get_data(ubq))
+				goto out;
+		} else if (ub_cmd->addr) {
+			/* User copy requires addr to be unset */
+			ret = -EINVAL;
+			goto out;
+		}
+
+		ublk_fill_io_cmd(io, cmd, ub_cmd->addr);
+		ublk_mark_io_ready(ub, ubq);
+		break;
+	case UBLK_IO_COMMIT_AND_FETCH_REQ:
+		req = blk_mq_tag_to_rq(ub->tag_set.tags[ub_cmd->q_id], tag);
+
+		if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
+			goto out;
+
+		if (!ublk_support_user_copy(ubq)) {
+			/*
+			 * COMMIT_AND_FETCH_REQ has to provide IO buffer if
+			 * NEED GET DATA is not enabled or it is Read IO.
+			 */
+			if (!ub_cmd->addr && (!ublk_need_get_data(ubq) ||
+						req_op(req) == REQ_OP_READ))
+				goto out;
+		} else if (req_op(req) != REQ_OP_ZONE_APPEND && ub_cmd->addr) {
+			/*
+			 * User copy requires addr to be unset when command is
+			 * not zone append
+			 */
+			ret = -EINVAL;
+			goto out;
+		}
+
+		ublk_fill_io_cmd(io, cmd, ub_cmd->addr);
+		ublk_commit_completion(ub, ub_cmd);
+		break;
+	case UBLK_IO_NEED_GET_DATA:
+		if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
+			goto out;
+		ublk_fill_io_cmd(io, cmd, ub_cmd->addr);
+		ublk_handle_need_get_data(ub, ub_cmd->q_id, ub_cmd->tag);
+		break;
+	default:
+		goto out;
+	}
+	return -EIOCBQUEUED;
+
+ out:
+	io_uring_cmd_done(cmd, ret, 0, issue_flags);
+	pr_devel("%s: complete: cmd op %d, tag %d ret %x io_flags %x\n",
+			__func__, cmd_op, tag, ret, io->flags);
+	return -EIOCBQUEUED;
+}
+
+static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
+		struct ublk_queue *ubq, int tag, size_t offset)
+{
+	struct request *req;
+
+	if (!ublk_need_req_ref(ubq))
+		return NULL;
+
+	req = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], tag);
+	if (!req)
+		return NULL;
+
+	if (!ublk_get_req_ref(ubq, req))
+		return NULL;
+
+	if (unlikely(!blk_mq_request_started(req) || req->tag != tag))
+		goto fail_put;
+
+	if (!ublk_rq_has_data(req))
+		goto fail_put;
+
+	if (offset > blk_rq_bytes(req))
+		goto fail_put;
+
+	return req;
+fail_put:
+	ublk_put_req_ref(ubq, req);
+	return NULL;
+}
+
+static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
+{
+	/*
+	 * Not necessary for async retry, but let's keep it simple and always
+	 * copy the values to avoid any potential reuse.
+	 */
+	const struct ublksrv_io_cmd *ub_src = io_uring_sqe_cmd(cmd->sqe);
+	const struct ublksrv_io_cmd ub_cmd = {
+		.q_id = READ_ONCE(ub_src->q_id),
+		.tag = READ_ONCE(ub_src->tag),
+		.result = READ_ONCE(ub_src->result),
+		.addr = READ_ONCE(ub_src->addr)
+	};
+
+	return __ublk_ch_uring_cmd(cmd, issue_flags, &ub_cmd);
+}
+
+static inline bool ublk_check_ubuf_dir(const struct request *req,
+		int ubuf_dir)
+{
+	/* copy ubuf to request pages */
+	if ((req_op(req) == REQ_OP_READ || req_op(req) == REQ_OP_DRV_IN) &&
+	    ubuf_dir == ITER_SOURCE)
+		return true;
+
+	/* copy request pages to ubuf */
+	if ((req_op(req) == REQ_OP_WRITE ||
+	     req_op(req) == REQ_OP_ZONE_APPEND) &&
+	    ubuf_dir == ITER_DEST)
+		return true;
+
+	return false;
+}
+
+static struct request *ublk_check_and_get_req(struct kiocb *iocb,
+		struct iov_iter *iter, size_t *off, int dir)
+{
+	struct ublk_device *ub = iocb->ki_filp->private_data;
+	struct ublk_queue *ubq;
+	struct request *req;
+	size_t buf_off;
+	u16 tag, q_id;
+
+	if (!ub)
+		return ERR_PTR(-EACCES);
+
+	if (!user_backed_iter(iter))
+		return ERR_PTR(-EACCES);
+
+	if (ub->dev_info.state == UBLK_S_DEV_DEAD)
+		return ERR_PTR(-EACCES);
+
+	tag = ublk_pos_to_tag(iocb->ki_pos);
+	q_id = ublk_pos_to_hwq(iocb->ki_pos);
+	buf_off = ublk_pos_to_buf_off(iocb->ki_pos);
+
+	if (q_id >= ub->dev_info.nr_hw_queues)
+		return ERR_PTR(-EINVAL);
+
+	ubq = ublk_get_queue(ub, q_id);
+	if (!ubq)
+		return ERR_PTR(-EINVAL);
+
+	if (tag >= ubq->q_depth)
+		return ERR_PTR(-EINVAL);
+
+	req = __ublk_check_and_get_req(ub, ubq, tag, buf_off);
+	if (!req)
+		return ERR_PTR(-EINVAL);
+
+	if (!req->mq_hctx || !req->mq_hctx->driver_data)
+		goto fail;
+
+	if (!ublk_check_ubuf_dir(req, dir))
+		goto fail;
+
+	*off = buf_off;
+	return req;
+fail:
+	ublk_put_req_ref(ubq, req);
+	return ERR_PTR(-EACCES);
+}
+
+static ssize_t ublk_ch_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct ublk_queue *ubq;
+	struct request *req;
+	size_t buf_off;
+	size_t ret;
+
+	req = ublk_check_and_get_req(iocb, to, &buf_off, ITER_DEST);
+	if (IS_ERR(req))
+		return PTR_ERR(req);
+
+	ret = ublk_copy_user_pages(req, buf_off, to, ITER_DEST);
+	ubq = req->mq_hctx->driver_data;
+	ublk_put_req_ref(ubq, req);
+
+	return ret;
+}
+
+static ssize_t ublk_ch_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct ublk_queue *ubq;
+	struct request *req;
+	size_t buf_off;
+	size_t ret;
+
+	req = ublk_check_and_get_req(iocb, from, &buf_off, ITER_SOURCE);
+	if (IS_ERR(req))
+		return PTR_ERR(req);
+
+	ret = ublk_copy_user_pages(req, buf_off, from, ITER_SOURCE);
+	ubq = req->mq_hctx->driver_data;
+	ublk_put_req_ref(ubq, req);
+
+	return ret;
+}
+
+static const struct file_operations ublk_ch_fops = {
+	.owner = THIS_MODULE,
+	.open = ublk_ch_open,
+	.release = ublk_ch_release,
+	.llseek = no_llseek,
+	.read_iter = ublk_ch_read_iter,
+	.write_iter = ublk_ch_write_iter,
+	.uring_cmd = ublk_ch_uring_cmd,
+	.mmap = ublk_ch_mmap,
+};
+
+static void ublk_deinit_queue(struct ublk_device *ub, int q_id)
+{
+	int size = ublk_queue_cmd_buf_size(ub, q_id);
+	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);
+
+	if (ubq->ubq_daemon)
+		put_task_struct(ubq->ubq_daemon);
+	if (ubq->io_cmd_buf)
+		free_pages((unsigned long)ubq->io_cmd_buf, get_order(size));
+}
+
+static int ublk_init_queue(struct ublk_device *ub, int q_id)
+{
+	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);
+	gfp_t gfp_flags = GFP_KERNEL | __GFP_ZERO;
+	void *ptr;
+	int size;
+
+	ubq->flags = ub->dev_info.flags;
+	ubq->q_id = q_id;
+	ubq->q_depth = ub->dev_info.queue_depth;
+	size = ublk_queue_cmd_buf_size(ub, q_id);
+
+	ptr = (void *) __get_free_pages(gfp_flags, get_order(size));
+	if (!ptr)
+		return -ENOMEM;
+
+	ubq->io_cmd_buf = ptr;
+	ubq->dev = ub;
+	return 0;
+}
+
+static void ublk_deinit_queues(struct ublk_device *ub)
+{
+	int nr_queues = ub->dev_info.nr_hw_queues;
+	int i;
+
+	if (!ub->__queues)
+		return;
+
+	for (i = 0; i < nr_queues; i++)
+		ublk_deinit_queue(ub, i);
+	kfree(ub->__queues);
+}
+
+static int ublk_init_queues(struct ublk_device *ub)
+{
+	int nr_queues = ub->dev_info.nr_hw_queues;
+	int depth = ub->dev_info.queue_depth;
+	int ubq_size = sizeof(struct ublk_queue) + depth * sizeof(struct ublk_io);
+	int i, ret = -ENOMEM;
+
+	ub->queue_size = ubq_size;
+	ub->__queues = kcalloc(nr_queues, ubq_size, GFP_KERNEL);
+	if (!ub->__queues)
+		return ret;
+
+	for (i = 0; i < nr_queues; i++) {
+		if (ublk_init_queue(ub, i))
+			goto fail;
+	}
+
+	init_completion(&ub->completion);
+	return 0;
+
+ fail:
+	ublk_deinit_queues(ub);
+	return ret;
+}
+
+static int ublk_alloc_dev_number(struct ublk_device *ub, int idx)
+{
+	int i = idx;
+	int err;
+
+	spin_lock(&ublk_idr_lock);
+	/* allocate id, if @id >= 0, we're requesting that specific id */
+	if (i >= 0) {
+		err = idr_alloc(&ublk_index_idr, ub, i, i + 1, GFP_NOWAIT);
+		if (err == -ENOSPC)
+			err = -EEXIST;
+	} else {
+		err = idr_alloc(&ublk_index_idr, ub, 0, 0, GFP_NOWAIT);
+	}
+	spin_unlock(&ublk_idr_lock);
+
+	if (err >= 0)
+		ub->ub_number = err;
+
+	return err;
+}
+
+static void ublk_free_dev_number(struct ublk_device *ub)
+{
+	spin_lock(&ublk_idr_lock);
+	idr_remove(&ublk_index_idr, ub->ub_number);
+	wake_up_all(&ublk_idr_wq);
+	spin_unlock(&ublk_idr_lock);
+}
+
+static void ublk_cdev_rel(struct device *dev)
+{
+	struct ublk_device *ub = container_of(dev, struct ublk_device, cdev_dev);
+
+	blk_mq_free_tag_set(&ub->tag_set);
+	ublk_deinit_queues(ub);
+	ublk_free_dev_number(ub);
+	mutex_destroy(&ub->mutex);
+	kfree(ub);
+}
+
+static int ublk_add_chdev(struct ublk_device *ub)
+{
+	struct device *dev = &ub->cdev_dev;
+	int minor = ub->ub_number;
+	int ret;
+
+	dev->parent = ublk_misc.this_device;
+	dev->devt = MKDEV(MAJOR(ublk_chr_devt), minor);
+	dev->class = &ublk_chr_class;
+	dev->release = ublk_cdev_rel;
+	device_initialize(dev);
+
+	ret = dev_set_name(dev, "ublkc%d", minor);
+	if (ret)
+		goto fail;
+
+	cdev_init(&ub->cdev, &ublk_ch_fops);
+	ret = cdev_device_add(&ub->cdev, dev);
+	if (ret)
+		goto fail;
+
+	ublks_added++;
+	return 0;
+ fail:
+	put_device(dev);
+	return ret;
+}
+
+static void ublk_stop_work_fn(struct work_struct *work)
+{
+	struct ublk_device *ub =
+		container_of(work, struct ublk_device, stop_work);
+
+	ublk_stop_dev(ub);
+}
+
+/* align max io buffer size with PAGE_SIZE */
+static void ublk_align_max_io_size(struct ublk_device *ub)
+{
+	unsigned int max_io_bytes = ub->dev_info.max_io_buf_bytes;
+
+	ub->dev_info.max_io_buf_bytes =
+		round_down(max_io_bytes, PAGE_SIZE);
+}
+
+static int ublk_add_tag_set(struct ublk_device *ub)
+{
+	ub->tag_set.ops = &ublk_mq_ops;
+	ub->tag_set.nr_hw_queues = ub->dev_info.nr_hw_queues;
+	ub->tag_set.queue_depth = ub->dev_info.queue_depth;
+	ub->tag_set.numa_node = NUMA_NO_NODE;
+	ub->tag_set.cmd_size = sizeof(struct ublk_rq_data);
+	ub->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
+	ub->tag_set.driver_data = ub;
+	return blk_mq_alloc_tag_set(&ub->tag_set);
+}
+
+static void ublk_remove(struct ublk_device *ub)
+{
+	ublk_stop_dev(ub);
+	cancel_work_sync(&ub->stop_work);
+	cancel_work_sync(&ub->quiesce_work);
+	cdev_device_del(&ub->cdev, &ub->cdev_dev);
+	put_device(&ub->cdev_dev);
+	ublks_added--;
+}
+
+static struct ublk_device *ublk_get_device_from_id(int idx)
+{
+	struct ublk_device *ub = NULL;
+
+	if (idx < 0)
+		return NULL;
+
+	spin_lock(&ublk_idr_lock);
+	ub = idr_find(&ublk_index_idr, idx);
+	if (ub)
+		ub = ublk_get_device(ub);
+	spin_unlock(&ublk_idr_lock);
+
+	return ub;
+}
+
+static int ublk_ctrl_start_dev(struct ublk_device *ub, struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	int ublksrv_pid = (int)header->data[0];
+	struct gendisk *disk;
+	int ret = -EINVAL;
+
+	if (ublksrv_pid <= 0)
+		return -EINVAL;
+
+	if (wait_for_completion_interruptible(&ub->completion) != 0)
+		return -EINTR;
+
+	schedule_delayed_work(&ub->monitor_work, UBLK_DAEMON_MONITOR_PERIOD);
+
+	mutex_lock(&ub->mutex);
+	if (ub->dev_info.state == UBLK_S_DEV_LIVE ||
+	    test_bit(UB_STATE_USED, &ub->state)) {
+		ret = -EEXIST;
+		goto out_unlock;
+	}
+
+	disk = blk_mq_alloc_disk(&ub->tag_set, NULL);
+	if (IS_ERR(disk)) {
+		ret = PTR_ERR(disk);
+		goto out_unlock;
+	}
+	sprintf(disk->disk_name, "ublkb%d", ub->ub_number);
+	disk->fops = &ub_fops;
+	disk->private_data = ub;
+
+	ub->dev_info.ublksrv_pid = ublksrv_pid;
+	ub->ub_disk = disk;
+
+	ret = ublk_apply_params(ub);
+	if (ret)
+		goto out_put_disk;
+
+	/* don't probe partitions if any one ubq daemon is un-trusted */
+	if (ub->nr_privileged_daemon != ub->nr_queues_ready)
+		set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
+
+	get_device(&ub->cdev_dev);
+	ub->dev_info.state = UBLK_S_DEV_LIVE;
+
+	if (ublk_dev_is_zoned(ub)) {
+		ret = ublk_revalidate_disk_zones(ub);
+		if (ret)
+			goto out_put_cdev;
+	}
+
+	ret = add_disk(disk);
+	if (ret)
+		goto out_put_cdev;
+
+	set_bit(UB_STATE_USED, &ub->state);
+
+out_put_cdev:
+	if (ret) {
+		ub->dev_info.state = UBLK_S_DEV_DEAD;
+		ublk_put_device(ub);
+	}
+out_put_disk:
+	if (ret)
+		put_disk(disk);
+out_unlock:
+	mutex_unlock(&ub->mutex);
+	return ret;
+}
+
+static int ublk_ctrl_get_queue_affinity(struct ublk_device *ub,
+		struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	void __user *argp = (void __user *)(unsigned long)header->addr;
+	cpumask_var_t cpumask;
+	unsigned long queue;
+	unsigned int retlen;
+	unsigned int i;
+	int ret;
+
+	if (header->len * BITS_PER_BYTE < nr_cpu_ids)
+		return -EINVAL;
+	if (header->len & (sizeof(unsigned long)-1))
+		return -EINVAL;
+	if (!header->addr)
+		return -EINVAL;
+
+	queue = header->data[0];
+	if (queue >= ub->dev_info.nr_hw_queues)
+		return -EINVAL;
+
+	if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
+		return -ENOMEM;
+
+	for_each_possible_cpu(i) {
+		if (ub->tag_set.map[HCTX_TYPE_DEFAULT].mq_map[i] == queue)
+			cpumask_set_cpu(i, cpumask);
+	}
+
+	ret = -EFAULT;
+	retlen = min_t(unsigned short, header->len, cpumask_size());
+	if (copy_to_user(argp, cpumask, retlen))
+		goto out_free_cpumask;
+	if (retlen != header->len &&
+	    clear_user(argp + retlen, header->len - retlen))
+		goto out_free_cpumask;
+
+	ret = 0;
+out_free_cpumask:
+	free_cpumask_var(cpumask);
+	return ret;
+}
+
+static inline void ublk_dump_dev_info(struct ublksrv_ctrl_dev_info *info)
+{
+	pr_devel("%s: dev id %d flags %llx\n", __func__,
+			info->dev_id, info->flags);
+	pr_devel("\t nr_hw_queues %d queue_depth %d\n",
+			info->nr_hw_queues, info->queue_depth);
+}
+
+static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	void __user *argp = (void __user *)(unsigned long)header->addr;
+	struct ublksrv_ctrl_dev_info info;
+	struct ublk_device *ub;
+	int ret = -EINVAL;
+
+	if (header->len < sizeof(info) || !header->addr)
+		return -EINVAL;
+	if (header->queue_id != (u16)-1) {
+		pr_warn("%s: queue_id is wrong %x\n",
+			__func__, header->queue_id);
+		return -EINVAL;
+	}
+
+	if (copy_from_user(&info, argp, sizeof(info)))
+		return -EFAULT;
+
+	if (capable(CAP_SYS_ADMIN))
+		info.flags &= ~UBLK_F_UNPRIVILEGED_DEV;
+	else if (!(info.flags & UBLK_F_UNPRIVILEGED_DEV))
+		return -EPERM;
+
+	/*
+	 * unprivileged device can't be trusted, but RECOVERY and
+	 * RECOVERY_REISSUE still may hang error handling, so can't
+	 * support recovery features for unprivileged ublk now
+	 *
+	 * TODO: provide forward progress for RECOVERY handler, so that
+	 * unprivileged device can benefit from it
+	 */
+	if (info.flags & UBLK_F_UNPRIVILEGED_DEV)
+		info.flags &= ~(UBLK_F_USER_RECOVERY_REISSUE |
+				UBLK_F_USER_RECOVERY);
+
+	/* the created device is always owned by current user */
+	ublk_store_owner_uid_gid(&info.owner_uid, &info.owner_gid);
+
+	if (header->dev_id != info.dev_id) {
+		pr_warn("%s: dev id not match %u %u\n",
+			__func__, header->dev_id, info.dev_id);
+		return -EINVAL;
+	}
+
+	ublk_dump_dev_info(&info);
+
+	ret = mutex_lock_killable(&ublk_ctl_mutex);
+	if (ret)
+		return ret;
+
+	ret = -EACCES;
+	if (ublks_added >= ublks_max)
+		goto out_unlock;
+
+	ret = -ENOMEM;
+	ub = kzalloc(sizeof(*ub), GFP_KERNEL);
+	if (!ub)
+		goto out_unlock;
+	mutex_init(&ub->mutex);
+	spin_lock_init(&ub->mm_lock);
+	INIT_WORK(&ub->quiesce_work, ublk_quiesce_work_fn);
+	INIT_WORK(&ub->stop_work, ublk_stop_work_fn);
+	INIT_DELAYED_WORK(&ub->monitor_work, ublk_daemon_monitor_work);
+
+	ret = ublk_alloc_dev_number(ub, header->dev_id);
+	if (ret < 0)
+		goto out_free_ub;
+
+	memcpy(&ub->dev_info, &info, sizeof(info));
+
+	/* update device id */
+	ub->dev_info.dev_id = ub->ub_number;
+
+	/*
+	 * 64bit flags will be copied back to userspace as feature
+	 * negotiation result, so have to clear flags which driver
+	 * doesn't support yet, then userspace can get correct flags
+	 * (features) to handle.
+	 */
+	ub->dev_info.flags &= UBLK_F_ALL;
+
+	ub->dev_info.flags |= UBLK_F_CMD_IOCTL_ENCODE |
+		UBLK_F_URING_CMD_COMP_IN_TASK;
+
+	/* GET_DATA isn't needed any more with USER_COPY */
+	if (ublk_dev_is_user_copy(ub))
+		ub->dev_info.flags &= ~UBLK_F_NEED_GET_DATA;
+
+	/* Zoned storage support requires user copy feature */
+	if (ublk_dev_is_zoned(ub) &&
+	    (!IS_ENABLED(CONFIG_BLK_DEV_ZONED) || !ublk_dev_is_user_copy(ub))) {
+		ret = -EINVAL;
+		goto out_free_dev_number;
+	}
+
+	/* We are not ready to support zero copy */
+	ub->dev_info.flags &= ~UBLK_F_SUPPORT_ZERO_COPY;
+
+	ub->dev_info.nr_hw_queues = min_t(unsigned int,
+			ub->dev_info.nr_hw_queues, nr_cpu_ids);
+	ublk_align_max_io_size(ub);
+
+	ret = ublk_init_queues(ub);
+	if (ret)
+		goto out_free_dev_number;
+
+	ret = ublk_add_tag_set(ub);
+	if (ret)
+		goto out_deinit_queues;
+
+	ret = -EFAULT;
+	if (copy_to_user(argp, &ub->dev_info, sizeof(info)))
+		goto out_free_tag_set;
+
+	/*
+	 * Add the char dev so that ublksrv daemon can be setup.
+	 * ublk_add_chdev() will cleanup everything if it fails.
+	 */
+	ret = ublk_add_chdev(ub);
+	goto out_unlock;
+
+out_free_tag_set:
+	blk_mq_free_tag_set(&ub->tag_set);
+out_deinit_queues:
+	ublk_deinit_queues(ub);
+out_free_dev_number:
+	ublk_free_dev_number(ub);
+out_free_ub:
+	mutex_destroy(&ub->mutex);
+	kfree(ub);
+out_unlock:
+	mutex_unlock(&ublk_ctl_mutex);
+	return ret;
+}
+
+static inline bool ublk_idr_freed(int id)
+{
+	void *ptr;
+
+	spin_lock(&ublk_idr_lock);
+	ptr = idr_find(&ublk_index_idr, id);
+	spin_unlock(&ublk_idr_lock);
+
+	return ptr == NULL;
+}
+
+static int ublk_ctrl_del_dev(struct ublk_device **p_ub)
+{
+	struct ublk_device *ub = *p_ub;
+	int idx = ub->ub_number;
+	int ret;
+
+	ret = mutex_lock_killable(&ublk_ctl_mutex);
+	if (ret)
+		return ret;
+
+	if (!test_bit(UB_STATE_DELETED, &ub->state)) {
+		ublk_remove(ub);
+		set_bit(UB_STATE_DELETED, &ub->state);
+	}
+
+	/* Mark the reference as consumed */
+	*p_ub = NULL;
+	ublk_put_device(ub);
+	mutex_unlock(&ublk_ctl_mutex);
+
+	/*
+	 * Wait until the idr is removed, then it can be reused after
+	 * DEL_DEV command is returned.
+	 *
+	 * If we returns because of user interrupt, future delete command
+	 * may come:
+	 *
+	 * - the device number isn't freed, this device won't or needn't
+	 *   be deleted again, since UB_STATE_DELETED is set, and device
+	 *   will be released after the last reference is dropped
+	 *
+	 * - the device number is freed already, we will not find this
+	 *   device via ublk_get_device_from_id()
+	 */
+	if (wait_event_interruptible(ublk_idr_wq, ublk_idr_freed(idx)))
+		return -EINTR;
+	return 0;
+}
+
+static inline void ublk_ctrl_cmd_dump(struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+
+	pr_devel("%s: cmd_op %x, dev id %d qid %d data %llx buf %llx len %u\n",
+			__func__, cmd->cmd_op, header->dev_id, header->queue_id,
+			header->data[0], header->addr, header->len);
+}
+
+static int ublk_ctrl_stop_dev(struct ublk_device *ub)
+{
+	ublk_stop_dev(ub);
+	cancel_work_sync(&ub->stop_work);
+	cancel_work_sync(&ub->quiesce_work);
+
+	return 0;
+}
+
+static int ublk_ctrl_get_dev_info(struct ublk_device *ub,
+		struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	void __user *argp = (void __user *)(unsigned long)header->addr;
+
+	if (header->len < sizeof(struct ublksrv_ctrl_dev_info) || !header->addr)
+		return -EINVAL;
+
+	if (copy_to_user(argp, &ub->dev_info, sizeof(ub->dev_info)))
+		return -EFAULT;
+
+	return 0;
+}
+
+/* TYPE_DEVT is readonly, so fill it up before returning to userspace */
+static void ublk_ctrl_fill_params_devt(struct ublk_device *ub)
+{
+	ub->params.devt.char_major = MAJOR(ub->cdev_dev.devt);
+	ub->params.devt.char_minor = MINOR(ub->cdev_dev.devt);
+
+	if (ub->ub_disk) {
+		ub->params.devt.disk_major = MAJOR(disk_devt(ub->ub_disk));
+		ub->params.devt.disk_minor = MINOR(disk_devt(ub->ub_disk));
+	} else {
+		ub->params.devt.disk_major = 0;
+		ub->params.devt.disk_minor = 0;
+	}
+	ub->params.types |= UBLK_PARAM_TYPE_DEVT;
+}
+
+static int ublk_ctrl_get_params(struct ublk_device *ub,
+		struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	void __user *argp = (void __user *)(unsigned long)header->addr;
+	struct ublk_params_header ph;
+	int ret;
+
+	if (header->len <= sizeof(ph) || !header->addr)
+		return -EINVAL;
+
+	if (copy_from_user(&ph, argp, sizeof(ph)))
+		return -EFAULT;
+
+	if (ph.len > header->len || !ph.len)
+		return -EINVAL;
+
+	if (ph.len > sizeof(struct ublk_params))
+		ph.len = sizeof(struct ublk_params);
+
+	mutex_lock(&ub->mutex);
+	ublk_ctrl_fill_params_devt(ub);
+	if (copy_to_user(argp, &ub->params, ph.len))
+		ret = -EFAULT;
+	else
+		ret = 0;
+	mutex_unlock(&ub->mutex);
+
+	return ret;
+}
+
+static int ublk_ctrl_set_params(struct ublk_device *ub,
+		struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	void __user *argp = (void __user *)(unsigned long)header->addr;
+	struct ublk_params_header ph;
+	int ret = -EFAULT;
+
+	if (header->len <= sizeof(ph) || !header->addr)
+		return -EINVAL;
+
+	if (copy_from_user(&ph, argp, sizeof(ph)))
+		return -EFAULT;
+
+	if (ph.len > header->len || !ph.len || !ph.types)
+		return -EINVAL;
+
+	if (ph.len > sizeof(struct ublk_params))
+		ph.len = sizeof(struct ublk_params);
+
+	/* parameters can only be changed when device isn't live */
+	mutex_lock(&ub->mutex);
+	if (ub->dev_info.state == UBLK_S_DEV_LIVE) {
+		ret = -EACCES;
+	} else if (copy_from_user(&ub->params, argp, ph.len)) {
+		ret = -EFAULT;
+	} else {
+		/* clear all we don't support yet */
+		ub->params.types &= UBLK_PARAM_TYPE_ALL;
+		ret = ublk_validate_params(ub);
+		if (ret)
+			ub->params.types = 0;
+	}
+	mutex_unlock(&ub->mutex);
+
+	return ret;
+}
+
+static void ublk_queue_reinit(struct ublk_device *ub, struct ublk_queue *ubq)
+{
+	int i;
+
+	WARN_ON_ONCE(!(ubq->ubq_daemon && ubq_daemon_is_dying(ubq)));
+	/* All old ioucmds have to be completed */
+	WARN_ON_ONCE(ubq->nr_io_ready);
+	/* old daemon is PF_EXITING, put it now */
+	put_task_struct(ubq->ubq_daemon);
+	/* We have to reset it to NULL, otherwise ub won't accept new FETCH_REQ */
+	ubq->ubq_daemon = NULL;
+	ubq->timeout = false;
+
+	for (i = 0; i < ubq->q_depth; i++) {
+		struct ublk_io *io = &ubq->ios[i];
+
+		/* forget everything now and be ready for new FETCH_REQ */
+		io->flags = 0;
+		io->cmd = NULL;
+		io->addr = 0;
+	}
+}
+
+static int ublk_ctrl_start_recovery(struct ublk_device *ub,
+		struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	int ret = -EINVAL;
+	int i;
+
+	mutex_lock(&ub->mutex);
+	if (!ublk_can_use_recovery(ub))
+		goto out_unlock;
+	/*
+	 * START_RECOVERY is only allowd after:
+	 *
+	 * (1) UB_STATE_OPEN is not set, which means the dying process is exited
+	 *     and related io_uring ctx is freed so file struct of /dev/ublkcX is
+	 *     released.
+	 *
+	 * (2) UBLK_S_DEV_QUIESCED is set, which means the quiesce_work:
+	 *     (a)has quiesced request queue
+	 *     (b)has requeued every inflight rqs whose io_flags is ACTIVE
+	 *     (c)has requeued/aborted every inflight rqs whose io_flags is NOT ACTIVE
+	 *     (d)has completed/camceled all ioucmds owned by ther dying process
+	 */
+	if (test_bit(UB_STATE_OPEN, &ub->state) ||
+			ub->dev_info.state != UBLK_S_DEV_QUIESCED) {
+		ret = -EBUSY;
+		goto out_unlock;
+	}
+	pr_devel("%s: start recovery for dev id %d.\n", __func__, header->dev_id);
+	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
+		ublk_queue_reinit(ub, ublk_get_queue(ub, i));
+	/* set to NULL, otherwise new ubq_daemon cannot mmap the io_cmd_buf */
+	ub->mm = NULL;
+	ub->nr_queues_ready = 0;
+	ub->nr_privileged_daemon = 0;
+	init_completion(&ub->completion);
+	ret = 0;
+ out_unlock:
+	mutex_unlock(&ub->mutex);
+	return ret;
+}
+
+static int ublk_ctrl_end_recovery(struct ublk_device *ub,
+		struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	int ublksrv_pid = (int)header->data[0];
+	int ret = -EINVAL;
+
+	pr_devel("%s: Waiting for new ubq_daemons(nr: %d) are ready, dev id %d...\n",
+			__func__, ub->dev_info.nr_hw_queues, header->dev_id);
+	/* wait until new ubq_daemon sending all FETCH_REQ */
+	if (wait_for_completion_interruptible(&ub->completion))
+		return -EINTR;
+
+	pr_devel("%s: All new ubq_daemons(nr: %d) are ready, dev id %d\n",
+			__func__, ub->dev_info.nr_hw_queues, header->dev_id);
+
+	mutex_lock(&ub->mutex);
+	if (!ublk_can_use_recovery(ub))
+		goto out_unlock;
+
+	if (ub->dev_info.state != UBLK_S_DEV_QUIESCED) {
+		ret = -EBUSY;
+		goto out_unlock;
+	}
+	ub->dev_info.ublksrv_pid = ublksrv_pid;
+	pr_devel("%s: new ublksrv_pid %d, dev id %d\n",
+			__func__, ublksrv_pid, header->dev_id);
+	blk_mq_unquiesce_queue(ub->ub_disk->queue);
+	pr_devel("%s: queue unquiesced, dev id %d.\n",
+			__func__, header->dev_id);
+	blk_mq_kick_requeue_list(ub->ub_disk->queue);
+	ub->dev_info.state = UBLK_S_DEV_LIVE;
+	schedule_delayed_work(&ub->monitor_work, UBLK_DAEMON_MONITOR_PERIOD);
+	ret = 0;
+ out_unlock:
+	mutex_unlock(&ub->mutex);
+	return ret;
+}
+
+static int ublk_ctrl_get_features(struct io_uring_cmd *cmd)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	void __user *argp = (void __user *)(unsigned long)header->addr;
+	u64 features = UBLK_F_ALL & ~UBLK_F_SUPPORT_ZERO_COPY;
+
+	if (header->len != UBLK_FEATURES_LEN || !header->addr)
+		return -EINVAL;
+
+	if (copy_to_user(argp, &features, UBLK_FEATURES_LEN))
+		return -EFAULT;
+
+	return 0;
+}
+
+/*
+ * All control commands are sent via /dev/ublk-control, so we have to check
+ * the destination device's permission
+ */
+static int ublk_char_dev_permission(struct ublk_device *ub,
+		const char *dev_path, int mask)
+{
+	int err;
+	struct path path;
+	struct kstat stat;
+
+	err = kern_path(dev_path, LOOKUP_FOLLOW, &path);
+	if (err)
+		return err;
+
+	err = vfs_getattr(&path, &stat, STATX_TYPE, AT_STATX_SYNC_AS_STAT);
+	if (err)
+		goto exit;
+
+	err = -EPERM;
+	if (stat.rdev != ub->cdev_dev.devt || !S_ISCHR(stat.mode))
+		goto exit;
+
+	err = inode_permission(&nop_mnt_idmap,
+			d_backing_inode(path.dentry), mask);
+exit:
+	path_put(&path);
+	return err;
+}
+
+static int ublk_ctrl_uring_cmd_permission(struct ublk_device *ub,
+		struct io_uring_cmd *cmd)
+{
+	struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)io_uring_sqe_cmd(cmd->sqe);
+	bool unprivileged = ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV;
+	void __user *argp = (void __user *)(unsigned long)header->addr;
+	char *dev_path = NULL;
+	int ret = 0;
+	int mask;
+
+	if (!unprivileged) {
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		/*
+		 * The new added command of UBLK_CMD_GET_DEV_INFO2 includes
+		 * char_dev_path in payload too, since userspace may not
+		 * know if the specified device is created as unprivileged
+		 * mode.
+		 */
+		if (_IOC_NR(cmd->cmd_op) != UBLK_CMD_GET_DEV_INFO2)
+			return 0;
+	}
+
+	/*
+	 * User has to provide the char device path for unprivileged ublk
+	 *
+	 * header->addr always points to the dev path buffer, and
+	 * header->dev_path_len records length of dev path buffer.
+	 */
+	if (!header->dev_path_len || header->dev_path_len > PATH_MAX)
+		return -EINVAL;
+
+	if (header->len < header->dev_path_len)
+		return -EINVAL;
+
+	dev_path = memdup_user_nul(argp, header->dev_path_len);
+	if (IS_ERR(dev_path))
+		return PTR_ERR(dev_path);
+
+	ret = -EINVAL;
+	switch (_IOC_NR(cmd->cmd_op)) {
+	case UBLK_CMD_GET_DEV_INFO:
+	case UBLK_CMD_GET_DEV_INFO2:
+	case UBLK_CMD_GET_QUEUE_AFFINITY:
+	case UBLK_CMD_GET_PARAMS:
+	case (_IOC_NR(UBLK_U_CMD_GET_FEATURES)):
+		mask = MAY_READ;
+		break;
+	case UBLK_CMD_START_DEV:
+	case UBLK_CMD_STOP_DEV:
+	case UBLK_CMD_ADD_DEV:
+	case UBLK_CMD_DEL_DEV:
+	case UBLK_CMD_SET_PARAMS:
+	case UBLK_CMD_START_USER_RECOVERY:
+	case UBLK_CMD_END_USER_RECOVERY:
+		mask = MAY_READ | MAY_WRITE;
+		break;
+	default:
+		goto exit;
+	}
+
+	ret = ublk_char_dev_permission(ub, dev_path, mask);
+	if (!ret) {
+		header->len -= header->dev_path_len;
+		header->addr += header->dev_path_len;
+	}
+	pr_devel("%s: dev id %d cmd_op %x uid %d gid %d path %s ret %d\n",
+			__func__, ub->ub_number, cmd->cmd_op,
+			ub->dev_info.owner_uid, ub->dev_info.owner_gid,
+			dev_path, ret);
+exit:
+	kfree(dev_path);
+	return ret;
+}
+
+static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
+		unsigned int issue_flags)
+{
+	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	struct ublk_device *ub = NULL;
+	u32 cmd_op = cmd->cmd_op;
+	int ret = -EINVAL;
+
+	if (issue_flags & IO_URING_F_NONBLOCK)
+		return -EAGAIN;
+
+	ublk_ctrl_cmd_dump(cmd);
+
+	if (!(issue_flags & IO_URING_F_SQE128))
+		goto out;
+
+	ret = ublk_check_cmd_op(cmd_op);
+	if (ret)
+		goto out;
+
+	if (cmd_op == UBLK_U_CMD_GET_FEATURES) {
+		ret = ublk_ctrl_get_features(cmd);
+		goto out;
+	}
+
+	if (_IOC_NR(cmd_op) != UBLK_CMD_ADD_DEV) {
+		ret = -ENODEV;
+		ub = ublk_get_device_from_id(header->dev_id);
+		if (!ub)
+			goto out;
+
+		ret = ublk_ctrl_uring_cmd_permission(ub, cmd);
+		if (ret)
+			goto put_dev;
+	}
+
+	switch (_IOC_NR(cmd_op)) {
+	case UBLK_CMD_START_DEV:
+		ret = ublk_ctrl_start_dev(ub, cmd);
+		break;
+	case UBLK_CMD_STOP_DEV:
+		ret = ublk_ctrl_stop_dev(ub);
+		break;
+	case UBLK_CMD_GET_DEV_INFO:
+	case UBLK_CMD_GET_DEV_INFO2:
+		ret = ublk_ctrl_get_dev_info(ub, cmd);
+		break;
+	case UBLK_CMD_ADD_DEV:
+		ret = ublk_ctrl_add_dev(cmd);
+		break;
+	case UBLK_CMD_DEL_DEV:
+		ret = ublk_ctrl_del_dev(&ub);
+		break;
+	case UBLK_CMD_GET_QUEUE_AFFINITY:
+		ret = ublk_ctrl_get_queue_affinity(ub, cmd);
+		break;
+	case UBLK_CMD_GET_PARAMS:
+		ret = ublk_ctrl_get_params(ub, cmd);
+		break;
+	case UBLK_CMD_SET_PARAMS:
+		ret = ublk_ctrl_set_params(ub, cmd);
+		break;
+	case UBLK_CMD_START_USER_RECOVERY:
+		ret = ublk_ctrl_start_recovery(ub, cmd);
+		break;
+	case UBLK_CMD_END_USER_RECOVERY:
+		ret = ublk_ctrl_end_recovery(ub, cmd);
+		break;
+	default:
+		ret = -ENOTSUPP;
+		break;
+	}
+
+ put_dev:
+	if (ub)
+		ublk_put_device(ub);
+ out:
+	io_uring_cmd_done(cmd, ret, 0, issue_flags);
+	pr_devel("%s: cmd done ret %d cmd_op %x, dev id %d qid %d\n",
+			__func__, ret, cmd->cmd_op, header->dev_id, header->queue_id);
+	return -EIOCBQUEUED;
+}
+
+static const struct file_operations ublk_ctl_fops = {
+	.open		= nonseekable_open,
+	.uring_cmd      = ublk_ctrl_uring_cmd,
+	.owner		= THIS_MODULE,
+	.llseek		= noop_llseek,
+};
+
+static struct miscdevice ublk_misc = {
+	.minor		= MISC_DYNAMIC_MINOR,
+	.name		= "ublk-control",
+	.fops		= &ublk_ctl_fops,
+};
+
+static int __init ublk_init(void)
+{
+	int ret;
+
+	BUILD_BUG_ON((u64)UBLKSRV_IO_BUF_OFFSET +
+			UBLKSRV_IO_BUF_TOTAL_SIZE < UBLKSRV_IO_BUF_OFFSET);
+
+	init_waitqueue_head(&ublk_idr_wq);
+
+	ret = misc_register(&ublk_misc);
+	if (ret)
+		return ret;
+
+	ret = alloc_chrdev_region(&ublk_chr_devt, 0, UBLK_MINORS, "ublk-char");
+	if (ret)
+		goto unregister_mis;
+
+	ret = class_register(&ublk_chr_class);
+	if (ret)
+		goto free_chrdev_region;
+
+	return 0;
+
+free_chrdev_region:
+	unregister_chrdev_region(ublk_chr_devt, UBLK_MINORS);
+unregister_mis:
+	misc_deregister(&ublk_misc);
+	return ret;
+}
+
+static void __exit ublk_exit(void)
+{
+	struct ublk_device *ub;
+	int id;
+
+	idr_for_each_entry(&ublk_index_idr, ub, id)
+		ublk_remove(ub);
+
+	class_unregister(&ublk_chr_class);
+	misc_deregister(&ublk_misc);
+
+	idr_destroy(&ublk_index_idr);
+	unregister_chrdev_region(ublk_chr_devt, UBLK_MINORS);
+}
+
+module_init(ublk_init);
+module_exit(ublk_exit);
+
+module_param(ublks_max, int, 0444);
+MODULE_PARM_DESC(ublks_max, "max number of ublk devices allowed to add(default: 64)");
+
+MODULE_AUTHOR("Ming Lei <ming.lei@redhat.com>");
+MODULE_LICENSE("GPL");