ublk_drv.c

// 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/cmd.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 <linux/kfifo.h>
#include <linux/blk-integrity.h>
#include <linux/maple_tree.h>
#include <linux/xarray.h>
#include <uapi/linux/fs.h>
#include <uapi/linux/ublk_cmd.h>

#define UBLK_MINORS		(1U << MINORBITS)

#define UBLK_INVALID_BUF_IDX 	((u16)-1)

/* private ioctl command mirror */
#define UBLK_CMD_DEL_DEV_ASYNC	_IOC_NR(UBLK_U_CMD_DEL_DEV_ASYNC)
#define UBLK_CMD_UPDATE_SIZE	_IOC_NR(UBLK_U_CMD_UPDATE_SIZE)
#define UBLK_CMD_QUIESCE_DEV	_IOC_NR(UBLK_U_CMD_QUIESCE_DEV)
#define UBLK_CMD_TRY_STOP_DEV	_IOC_NR(UBLK_U_CMD_TRY_STOP_DEV)
#define UBLK_CMD_REG_BUF	_IOC_NR(UBLK_U_CMD_REG_BUF)
#define UBLK_CMD_UNREG_BUF	_IOC_NR(UBLK_U_CMD_UNREG_BUF)

/* Default max shmem buffer size: 4GB (may be increased in future) */
#define UBLK_SHMEM_BUF_SIZE_MAX	(1ULL << 32)

#define UBLK_IO_REGISTER_IO_BUF		_IOC_NR(UBLK_U_IO_REGISTER_IO_BUF)
#define UBLK_IO_UNREGISTER_IO_BUF	_IOC_NR(UBLK_U_IO_UNREGISTER_IO_BUF)

/* 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 \
		| UBLK_F_USER_RECOVERY_FAIL_IO \
		| UBLK_F_UPDATE_SIZE \
		| UBLK_F_AUTO_BUF_REG \
		| UBLK_F_QUIESCE \
		| UBLK_F_PER_IO_DAEMON \
		| UBLK_F_BUF_REG_OFF_DAEMON \
		| (IS_ENABLED(CONFIG_BLK_DEV_INTEGRITY) ? UBLK_F_INTEGRITY : 0) \
		| UBLK_F_SAFE_STOP_DEV \
		| UBLK_F_BATCH_IO \
		| UBLK_F_NO_AUTO_PART_SCAN \
		| UBLK_F_SHMEM_ZC)

#define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \
		| UBLK_F_USER_RECOVERY_REISSUE \
		| UBLK_F_USER_RECOVERY_FAIL_IO)

/* 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 |    \
	 UBLK_PARAM_TYPE_DMA_ALIGN | UBLK_PARAM_TYPE_SEGMENT | \
	 UBLK_PARAM_TYPE_INTEGRITY)

#define UBLK_BATCH_F_ALL  \
	(UBLK_BATCH_F_HAS_ZONE_LBA | \
	 UBLK_BATCH_F_HAS_BUF_ADDR | \
	 UBLK_BATCH_F_AUTO_BUF_REG_FALLBACK)

/* ublk batch fetch uring_cmd */
struct ublk_batch_fetch_cmd {
	struct list_head node;
	struct io_uring_cmd *cmd;
	unsigned short buf_group;
};

struct ublk_uring_cmd_pdu {
	/*
	 * Store requests in same batch temporarily for queuing them to
	 * daemon context.
	 *
	 * It should have been stored to request payload, but we do want
	 * to avoid extra pre-allocation, and uring_cmd payload is always
	 * free for us
	 */
	union {
		struct request *req;
		struct request *req_list;
	};

	/*
	 * The following two are valid in this cmd whole lifetime, and
	 * setup in ublk uring_cmd handler
	 */
	struct ublk_queue *ubq;

	union {
		u16 tag;
		struct ublk_batch_fetch_cmd *fcmd; /* batch io only */
	};
};

struct ublk_batch_io_data {
	struct ublk_device *ub;
	struct io_uring_cmd *cmd;
	struct ublk_batch_io header;
	unsigned int issue_flags;
	struct io_comp_batch *iob;
};

/*
 * 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

/*
 * 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

/*
 * request buffer is registered automatically, so we have to unregister it
 * before completing this request.
 *
 * io_uring will unregister buffer automatically for us during exiting.
 */
#define UBLK_IO_FLAG_AUTO_BUF_REG 	0x10

/* atomic RW with ubq->cancel_lock */
#define UBLK_IO_FLAG_CANCELED	0x80000000

/*
 * Initialize refcount to a large number to include any registered buffers.
 * UBLK_IO_COMMIT_AND_FETCH_REQ will release these references minus those for
 * any buffers registered on the io daemon task.
 */
#define UBLK_REFCOUNT_INIT (REFCOUNT_MAX / 2)

/* used for UBLK_F_BATCH_IO only */
#define UBLK_BATCH_IO_UNUSED_TAG	((unsigned short)-1)

union ublk_io_buf {
	__u64	addr;
	struct ublk_auto_buf_reg auto_reg;
};

struct ublk_io {
	union ublk_io_buf buf;
	unsigned int flags;
	int res;

	union {
		/* valid if UBLK_IO_FLAG_ACTIVE is set */
		struct io_uring_cmd *cmd;
		/* valid if UBLK_IO_FLAG_OWNED_BY_SRV is set */
		struct request *req;
	};

	struct task_struct *task;

	/*
	 * The number of uses of this I/O by the ublk server
	 * if user copy or zero copy are enabled:
	 * - UBLK_REFCOUNT_INIT from dispatch to the server
	 *   until UBLK_IO_COMMIT_AND_FETCH_REQ
	 * - 1 for each inflight ublk_ch_{read,write}_iter() call not on task
	 * - 1 for each io_uring registered buffer not registered on task
	 * The I/O can only be completed once all references are dropped.
	 * User copy and buffer registration operations are only permitted
	 * if the reference count is nonzero.
	 */
	refcount_t ref;
	/* Count of buffers registered on task and not yet unregistered */
	unsigned task_registered_buffers;

	void *buf_ctx_handle;
	spinlock_t lock;
} ____cacheline_aligned_in_smp;

struct ublk_queue {
	int q_id;
	int q_depth;

	unsigned long flags;
	struct ublksrv_io_desc *io_cmd_buf;

	bool force_abort;
	bool canceling;
	bool fail_io; /* copy of dev->state == UBLK_S_DEV_FAIL_IO */
	spinlock_t		cancel_lock;
	struct ublk_device *dev;
	u32 nr_io_ready;

	/*
	 * For supporting UBLK_F_BATCH_IO only.
	 *
	 * Inflight ublk request tag is saved in this fifo
	 *
	 * There are multiple writer from ublk_queue_rq() or ublk_queue_rqs(),
	 * so lock is required for storing request tag to fifo
	 *
	 * Make sure just one reader for fetching request from task work
	 * function to ublk server, so no need to grab the lock in reader
	 * side.
	 *
	 * Batch I/O State Management:
	 *
	 * The batch I/O system uses implicit state management based on the
	 * combination of three key variables below.
	 *
	 * - IDLE: list_empty(&fcmd_head) && !active_fcmd
	 *   No fetch commands available, events queue in evts_fifo
	 *
	 * - READY: !list_empty(&fcmd_head) && !active_fcmd
	 *   Fetch commands available but none processing events
	 *
	 * - ACTIVE: active_fcmd
	 *   One fetch command actively processing events from evts_fifo
	 *
	 * Key Invariants:
	 * - At most one active_fcmd at any time (single reader)
	 * - active_fcmd is always from fcmd_head list when non-NULL
	 * - evts_fifo can be read locklessly by the single active reader
	 * - All state transitions require evts_lock protection
	 * - Multiple writers to evts_fifo require lock protection
	 */
	struct {
		DECLARE_KFIFO_PTR(evts_fifo, unsigned short);
		spinlock_t evts_lock;

		/* List of fetch commands available to process events */
		struct list_head fcmd_head;

		/* Currently active fetch command (NULL = none active) */
		struct ublk_batch_fetch_cmd  *active_fcmd;
	}____cacheline_aligned_in_smp;

	struct ublk_io ios[] __counted_by(q_depth);
};

/* Maple tree value: maps a PFN range to buffer location */
struct ublk_buf_range {
	unsigned short buf_index;
	unsigned short flags;
	unsigned int base_offset;	/* byte offset within buffer */
};

struct ublk_device {
	struct gendisk		*ub_disk;

	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		lock;
	struct mm_struct	*mm;

	struct ublk_params	params;

	struct completion	completion;
	u32			nr_queue_ready;
	bool 			unprivileged_daemons;
	struct mutex cancel_mutex;
	bool canceling;
	pid_t 	ublksrv_tgid;
	struct delayed_work	exit_work;
	struct work_struct	partition_scan_work;

	bool			block_open; /* protected by open_mutex */

	/* shared memory zero copy */
	struct maple_tree	buf_tree;
	struct ida		buf_ida;

	struct ublk_queue       *queues[];
};

/* header of ublk_params */
struct ublk_params_header {
	__u32	len;
	__u32	types;
};

static void ublk_io_release(void *priv);
static void ublk_stop_dev_unlocked(struct ublk_device *ub);
static bool ublk_try_buf_match(struct ublk_device *ub, struct request *rq,
				  u32 *buf_idx, u32 *buf_off);
static void ublk_buf_cleanup(struct ublk_device *ub);
static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq);
static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
		u16 q_id, u16 tag, struct ublk_io *io);
static inline unsigned int ublk_req_build_flags(struct request *req);
static void ublk_batch_dispatch(struct ublk_queue *ubq,
				const struct ublk_batch_io_data *data,
				struct ublk_batch_fetch_cmd *fcmd);

static inline bool ublk_dev_support_batch_io(const struct ublk_device *ub)
{
	return ub->dev_info.flags & UBLK_F_BATCH_IO;
}

static inline bool ublk_support_batch_io(const struct ublk_queue *ubq)
{
	return ubq->flags & UBLK_F_BATCH_IO;
}

static inline void ublk_io_lock(struct ublk_io *io)
{
	spin_lock(&io->lock);
}

static inline void ublk_io_unlock(struct ublk_io *io)
{
	spin_unlock(&io->lock);
}

/* Initialize the event queue */
static inline int ublk_io_evts_init(struct ublk_queue *q, unsigned int size,
				    int numa_node)
{
	spin_lock_init(&q->evts_lock);
	return kfifo_alloc_node(&q->evts_fifo, size, GFP_KERNEL, numa_node);
}

/* Check if event queue is empty */
static inline bool ublk_io_evts_empty(const struct ublk_queue *q)
{
	return kfifo_is_empty(&q->evts_fifo);
}

static inline void ublk_io_evts_deinit(struct ublk_queue *q)
{
	WARN_ON_ONCE(!kfifo_is_empty(&q->evts_fifo));
	kfifo_free(&q->evts_fifo);
}

static inline struct ublksrv_io_desc *
ublk_get_iod(const struct ublk_queue *ubq, unsigned tag)
{
	return &ubq->io_cmd_buf[tag];
}

static inline bool ublk_support_zero_copy(const struct ublk_queue *ubq)
{
	return ubq->flags & UBLK_F_SUPPORT_ZERO_COPY;
}

static inline bool ublk_dev_support_zero_copy(const struct ublk_device *ub)
{
	return ub->dev_info.flags & UBLK_F_SUPPORT_ZERO_COPY;
}

static inline bool ublk_support_shmem_zc(const struct ublk_queue *ubq)
{
	return ubq->flags & UBLK_F_SHMEM_ZC;
}

static inline bool ublk_iod_is_shmem_zc(const struct ublk_queue *ubq,
					unsigned int tag)
{
	return ublk_get_iod(ubq, tag)->op_flags & UBLK_IO_F_SHMEM_ZC;
}

static inline bool ublk_dev_support_shmem_zc(const struct ublk_device *ub)
{
	return ub->dev_info.flags & UBLK_F_SHMEM_ZC;
}

static inline bool ublk_support_auto_buf_reg(const struct ublk_queue *ubq)
{
	return ubq->flags & UBLK_F_AUTO_BUF_REG;
}

static inline bool ublk_dev_support_auto_buf_reg(const struct ublk_device *ub)
{
	return ub->dev_info.flags & UBLK_F_AUTO_BUF_REG;
}

static inline bool ublk_support_user_copy(const struct ublk_queue *ubq)
{
	return ubq->flags & UBLK_F_USER_COPY;
}

static inline bool ublk_dev_support_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(const struct ublk_queue *ubq)
{
	return ubq->flags & UBLK_F_ZONED;
}

static inline bool ublk_dev_support_integrity(const struct ublk_device *ub)
{
	return ub->dev_info.flags & UBLK_F_INTEGRITY;
}

#ifdef CONFIG_BLK_DEV_ZONED

struct ublk_zoned_report_desc {
	__u64 sector;
	__u32 operation;
	__u32 nr_zones;
};

static DEFINE_XARRAY(ublk_zoned_report_descs);

static int ublk_zoned_insert_report_desc(const struct request *req,
		struct ublk_zoned_report_desc *desc)
{
	return xa_insert(&ublk_zoned_report_descs, (unsigned long)req,
			    desc, GFP_KERNEL);
}

static struct ublk_zoned_report_desc *ublk_zoned_erase_report_desc(
		const struct request *req)
{
	return xa_erase(&ublk_zoned_report_descs, (unsigned long)req);
}

static struct ublk_zoned_report_desc *ublk_zoned_get_report_desc(
		const struct request *req)
{
	return xa_load(&ublk_zoned_report_descs, (unsigned long)req);
}

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);
}

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 void ublk_dev_param_zoned_apply(struct ublk_device *ub)
{
	ub->ub_disk->nr_zones = ublk_get_nr_zones(ub);
}

/* 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, struct blk_report_zones_args *args)
{
	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_zoned_report_desc desc;
		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;
		}

		desc.operation = UBLK_IO_OP_REPORT_ZONES;
		desc.sector = sector;
		desc.nr_zones = zones_in_request;
		ret = ublk_zoned_insert_report_desc(req, &desc);
		if (ret)
			goto free_req;

		ret = blk_rq_map_kern(req, buffer, buffer_length, GFP_KERNEL);
		if (ret)
			goto erase_desc;

		status = blk_execute_rq(req, 0);
		ret = blk_status_to_errno(status);
erase_desc:
		ublk_zoned_erase_report_desc(req);
free_req:
		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 = disk_report_zone(disk, zone, i, args);
			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_zoned_report_desc *desc;
	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:
		desc = ublk_zoned_get_report_desc(req);
		if (!desc)
			return BLK_STS_IOERR;
		ublk_op = desc->operation;
		switch (ublk_op) {
		case UBLK_IO_OP_REPORT_ZONES:
			iod->op_flags = ublk_op | ublk_req_build_flags(req);
			iod->nr_zones = desc->nr_zones;
			iod->start_sector = desc->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->buf.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 void ublk_dev_param_zoned_apply(struct ublk_device *ub)
{
}

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, struct ublk_io *io,
				      bool need_map, struct io_comp_batch *iob);

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);

static struct ublk_batch_fetch_cmd *
ublk_batch_alloc_fcmd(struct io_uring_cmd *cmd)
{
	struct ublk_batch_fetch_cmd *fcmd = kzalloc_obj(*fcmd, GFP_NOIO);

	if (fcmd) {
		fcmd->cmd = cmd;
		fcmd->buf_group = READ_ONCE(cmd->sqe->buf_index);
	}
	return fcmd;
}

static void ublk_batch_free_fcmd(struct ublk_batch_fetch_cmd *fcmd)
{
	kfree(fcmd);
}

static void __ublk_release_fcmd(struct ublk_queue *ubq)
{
	WRITE_ONCE(ubq->active_fcmd, NULL);
}

/*
 * Nothing can move on, so clear ->active_fcmd, and the caller should stop
 * dispatching
 */
static void ublk_batch_deinit_fetch_buf(struct ublk_queue *ubq,
					const struct ublk_batch_io_data *data,
					struct ublk_batch_fetch_cmd *fcmd,
					int res)
{
	spin_lock(&ubq->evts_lock);
	list_del_init(&fcmd->node);
	WARN_ON_ONCE(fcmd != ubq->active_fcmd);
	__ublk_release_fcmd(ubq);
	spin_unlock(&ubq->evts_lock);

	io_uring_cmd_done(fcmd->cmd, res, data->issue_flags);
	ublk_batch_free_fcmd(fcmd);
}

static int ublk_batch_fetch_post_cqe(struct ublk_batch_fetch_cmd *fcmd,
				     struct io_br_sel *sel,
				     unsigned int issue_flags)
{
	if (io_uring_mshot_cmd_post_cqe(fcmd->cmd, sel, issue_flags))
		return -ENOBUFS;
	return 0;
}

static ssize_t ublk_batch_copy_io_tags(struct ublk_batch_fetch_cmd *fcmd,
				       void __user *buf, const u16 *tag_buf,
				       unsigned int len)
{
	if (copy_to_user(buf, tag_buf, len))
		return -EFAULT;
	return len;
}

#define UBLK_MAX_UBLKS UBLK_MINORS

/*
 * Max unprivileged ublk devices allowed to add
 *
 * It can be extended to one per-user limit in future or even controlled
 * by cgroup.
 */
static unsigned int unprivileged_ublks_max = 64;
static unsigned int unprivileged_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)
{
	const struct ublk_param_basic *p = &ub->params.basic;

	if (p->attrs & UBLK_ATTR_READ_ONLY)
		set_disk_ro(ub->ub_disk, true);

	set_capacity(ub->ub_disk, p->dev_sectors);
}

static int ublk_integrity_flags(u32 flags)
{
	int ret_flags = BLK_SPLIT_INTERVAL_CAPABLE;

	if (flags & LBMD_PI_CAP_INTEGRITY) {
		flags &= ~LBMD_PI_CAP_INTEGRITY;
		ret_flags |= BLK_INTEGRITY_DEVICE_CAPABLE;
	}
	if (flags & LBMD_PI_CAP_REFTAG) {
		flags &= ~LBMD_PI_CAP_REFTAG;
		ret_flags |= BLK_INTEGRITY_REF_TAG;
	}
	return flags ? -EINVAL : ret_flags;
}

static int ublk_integrity_pi_tuple_size(u8 csum_type)
{
	switch (csum_type) {
	case LBMD_PI_CSUM_NONE:
		return 0;
	case LBMD_PI_CSUM_IP:
	case LBMD_PI_CSUM_CRC16_T10DIF:
		return 8;
	case LBMD_PI_CSUM_CRC64_NVME:
		return 16;
	default:
		return -EINVAL;
	}
}

static enum blk_integrity_checksum ublk_integrity_csum_type(u8 csum_type)
{
	switch (csum_type) {
	case LBMD_PI_CSUM_NONE:
		return BLK_INTEGRITY_CSUM_NONE;
	case LBMD_PI_CSUM_IP:
		return BLK_INTEGRITY_CSUM_IP;
	case LBMD_PI_CSUM_CRC16_T10DIF:
		return BLK_INTEGRITY_CSUM_CRC;
	case LBMD_PI_CSUM_CRC64_NVME:
		return BLK_INTEGRITY_CSUM_CRC64;
	default:
		WARN_ON_ONCE(1);
		return BLK_INTEGRITY_CSUM_NONE;
	}
}

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;

	if (ub->params.types & UBLK_PARAM_TYPE_DMA_ALIGN) {
		const struct ublk_param_dma_align *p = &ub->params.dma;

		if (p->alignment >= PAGE_SIZE)
			return -EINVAL;

		if (!is_power_of_2(p->alignment + 1))
			return -EINVAL;
	}

	if (ub->params.types & UBLK_PARAM_TYPE_SEGMENT) {
		const struct ublk_param_segment *p = &ub->params.seg;

		if (!is_power_of_2(p->seg_boundary_mask + 1))
			return -EINVAL;

		if (p->seg_boundary_mask + 1 < UBLK_MIN_SEGMENT_SIZE)
			return -EINVAL;
		if (p->max_segment_size < UBLK_MIN_SEGMENT_SIZE)
			return -EINVAL;
	}

	if (ub->params.types & UBLK_PARAM_TYPE_INTEGRITY) {
		const struct ublk_param_integrity *p = &ub->params.integrity;
		int pi_tuple_size = ublk_integrity_pi_tuple_size(p->csum_type);
		int flags = ublk_integrity_flags(p->flags);

		if (!ublk_dev_support_integrity(ub))
			return -EINVAL;
		if (flags < 0)
			return flags;
		if (pi_tuple_size < 0)
			return pi_tuple_size;
		if (!p->metadata_size)
			return -EINVAL;
		if (p->csum_type == LBMD_PI_CSUM_NONE &&
		    p->flags & LBMD_PI_CAP_REFTAG)
			return -EINVAL;
		if (p->pi_offset + pi_tuple_size > p->metadata_size)
			return -EINVAL;
		if (p->interval_exp < SECTOR_SHIFT ||
		    p->interval_exp > ub->params.basic.logical_bs_shift)
			return -EINVAL;
	}

	return 0;
}

static void ublk_apply_params(struct ublk_device *ub)
{
	ublk_dev_param_basic_apply(ub);

	if (ub->params.types & UBLK_PARAM_TYPE_ZONED)
		ublk_dev_param_zoned_apply(ub);
}

static inline bool ublk_need_map_io(const struct ublk_queue *ubq)
{
	return !ublk_support_user_copy(ubq) && !ublk_support_zero_copy(ubq) &&
		!ublk_support_auto_buf_reg(ubq);
}

static inline bool ublk_dev_need_map_io(const struct ublk_device *ub)
{
	return !ublk_dev_support_user_copy(ub) &&
	       !ublk_dev_support_zero_copy(ub) &&
	       !ublk_dev_support_auto_buf_reg(ub);
}

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
	 *
	 * for zero copy, request buffer need to be registered to io_uring
	 * buffer table, so reference is needed
	 *
	 * For auto buffer register, ublk server still may issue
	 * UBLK_IO_COMMIT_AND_FETCH_REQ before one registered buffer is used up,
	 * so reference is required too.
	 */
	return ublk_support_user_copy(ubq) || ublk_support_zero_copy(ubq) ||
		ublk_support_auto_buf_reg(ubq);
}

static inline bool ublk_dev_need_req_ref(const struct ublk_device *ub)
{
	return ublk_dev_support_user_copy(ub) ||
	       ublk_dev_support_zero_copy(ub) ||
	       ublk_dev_support_auto_buf_reg(ub);
}

/*
 * ublk IO Reference Counting Design
 * ==================================
 *
 * For user-copy and zero-copy modes, ublk uses a split reference model with
 * two counters that together track IO lifetime:
 *
 *   - io->ref: refcount for off-task buffer registrations and user-copy ops
 *   - io->task_registered_buffers: count of buffers registered on the IO task
 *
 * Key Invariant:
 * --------------
 * When IO is dispatched to the ublk server (UBLK_IO_FLAG_OWNED_BY_SRV set),
 * the sum (io->ref + io->task_registered_buffers) must equal UBLK_REFCOUNT_INIT
 * when no active references exist. After IO completion, both counters become
 * zero. For I/Os not currently dispatched to the ublk server, both ref and
 * task_registered_buffers are 0.
 *
 * This invariant is checked by ublk_check_and_reset_active_ref() during daemon
 * exit to determine if all references have been released.
 *
 * Why Split Counters:
 * -------------------
 * Buffers registered on the IO daemon task can use the lightweight
 * task_registered_buffers counter (simple increment/decrement) instead of
 * atomic refcount operations. The ublk_io_release() callback checks if
 * current == io->task to decide which counter to update.
 *
 * This optimization only applies before IO completion. At completion,
 * ublk_sub_req_ref() collapses task_registered_buffers into the atomic ref.
 * After that, all subsequent buffer unregistrations must use the atomic ref
 * since they may be releasing the last reference.
 *
 * Reference Lifecycle:
 * --------------------
 * 1. ublk_init_req_ref(): Sets io->ref = UBLK_REFCOUNT_INIT at IO dispatch
 *
 * 2. During IO processing:
 *    - On-task buffer reg: task_registered_buffers++ (no ref change)
 *    - Off-task buffer reg: ref++ via ublk_get_req_ref()
 *    - Buffer unregister callback (ublk_io_release):
 *      * If on-task: task_registered_buffers--
 *      * If off-task: ref-- via ublk_put_req_ref()
 *
 * 3. ublk_sub_req_ref() at IO completion:
 *    - Computes: sub_refs = UBLK_REFCOUNT_INIT - task_registered_buffers
 *    - Subtracts sub_refs from ref and zeroes task_registered_buffers
 *    - This effectively collapses task_registered_buffers into the atomic ref,
 *      accounting for the initial UBLK_REFCOUNT_INIT minus any on-task
 *      buffers that were already counted
 *
 * Example (zero-copy, register on-task, unregister off-task):
 *   - Dispatch: ref = UBLK_REFCOUNT_INIT, task_registered_buffers = 0
 *   - Register buffer on-task: task_registered_buffers = 1
 *   - Unregister off-task: ref-- (UBLK_REFCOUNT_INIT - 1), task_registered_buffers stays 1
 *   - Completion via ublk_sub_req_ref():
 *     sub_refs = UBLK_REFCOUNT_INIT - 1,
 *     ref = (UBLK_REFCOUNT_INIT - 1) - (UBLK_REFCOUNT_INIT - 1) = 0
 *
 * Example (auto buffer registration):
 *   Auto buffer registration sets task_registered_buffers = 1 at dispatch.
 *
 *   - Dispatch: ref = UBLK_REFCOUNT_INIT, task_registered_buffers = 1
 *   - Buffer unregister: task_registered_buffers-- (becomes 0)
 *   - Completion via ublk_sub_req_ref():
 *     sub_refs = UBLK_REFCOUNT_INIT - 0, ref becomes 0
 *
 * Example (zero-copy, ublk server killed):
 *   When daemon is killed, io_uring cleanup unregisters buffers off-task.
 *   ublk_check_and_reset_active_ref() waits for the invariant to hold.
 *
 *   - Dispatch: ref = UBLK_REFCOUNT_INIT, task_registered_buffers = 0
 *   - Register buffer on-task: task_registered_buffers = 1
 *   - Daemon killed, io_uring cleanup unregisters buffer (off-task):
 *     ref-- (UBLK_REFCOUNT_INIT - 1), task_registered_buffers stays 1
 *   - Daemon exit check: sum = (UBLK_REFCOUNT_INIT - 1) + 1 = UBLK_REFCOUNT_INIT
 *   - Sum equals UBLK_REFCOUNT_INIT, then both two counters are zeroed by
 *     ublk_check_and_reset_active_ref(), so ublk_abort_queue() can proceed
 *     and abort pending requests
 *
 * Batch IO Special Case:
 * ----------------------
 * In batch IO mode, io->task is NULL. This means ublk_io_release() always
 * takes the off-task path (ublk_put_req_ref), decrementing io->ref. The
 * task_registered_buffers counter still tracks registered buffers for the
 * invariant check, even though the callback doesn't decrement it.
 *
 * Note: updating task_registered_buffers is protected by io->lock.
 */
static inline void ublk_init_req_ref(const struct ublk_queue *ubq,
		struct ublk_io *io)
{
	if (ublk_need_req_ref(ubq))
		refcount_set(&io->ref, UBLK_REFCOUNT_INIT);
}

static inline bool ublk_get_req_ref(struct ublk_io *io)
{
	return refcount_inc_not_zero(&io->ref);
}

static inline void ublk_put_req_ref(struct ublk_io *io, struct request *req)
{
	if (!refcount_dec_and_test(&io->ref))
		return;

	/* ublk_need_map_io() and ublk_need_req_ref() are mutually exclusive */
	__ublk_complete_rq(req, io, false, NULL);
}

static inline bool ublk_sub_req_ref(struct ublk_io *io)
{
	unsigned sub_refs = UBLK_REFCOUNT_INIT - io->task_registered_buffers;

	io->task_registered_buffers = 0;
	return refcount_sub_and_test(sub_refs, &io->ref);
}

static inline bool ublk_need_get_data(const struct ublk_queue *ubq)
{
	return ubq->flags & UBLK_F_NEED_GET_DATA;
}

static inline bool ublk_dev_need_get_data(const struct ublk_device *ub)
{
	return ub->dev_info.flags & UBLK_F_NEED_GET_DATA;
}

/* Called in slow path only, keep it noinline for trace purpose */
static noinline struct ublk_device *ublk_get_device(struct ublk_device *ub)
{
	if (kobject_get_unless_zero(&ub->cdev_dev.kobj))
		return ub;
	return NULL;
}

/* Called in slow path only, keep it noinline for trace purpose */
static noinline 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 dev->queues[qid];
}

static inline bool ublk_rq_has_data(const struct request *rq)
{
	return blk_rq_bytes(rq);
}

static inline struct ublksrv_io_desc *
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(int depth)
{
	return round_up(depth * sizeof(struct ublksrv_io_desc), PAGE_SIZE);
}

static inline int ublk_queue_cmd_buf_size(struct ublk_device *ub)
{
	return __ublk_queue_cmd_buf_size(ub->dev_info.queue_depth);
}

static int ublk_max_cmd_buf_size(void)
{
	return __ublk_queue_cmd_buf_size(UBLK_MAX_QUEUE_DEPTH);
}

/*
 * Should I/O outstanding to the ublk server when it exits be reissued?
 * If not, outstanding I/O will get errors.
 */
static inline bool ublk_nosrv_should_reissue_outstanding(struct ublk_device *ub)
{
	return (ub->dev_info.flags & UBLK_F_USER_RECOVERY) &&
	       (ub->dev_info.flags & UBLK_F_USER_RECOVERY_REISSUE);
}

/*
 * Should I/O issued while there is no ublk server queue? If not, I/O
 * issued while there is no ublk server will get errors.
 */
static inline bool ublk_nosrv_dev_should_queue_io(struct ublk_device *ub)
{
	return (ub->dev_info.flags & UBLK_F_USER_RECOVERY) &&
	       !(ub->dev_info.flags & UBLK_F_USER_RECOVERY_FAIL_IO);
}

/*
 * Same as ublk_nosrv_dev_should_queue_io, but uses a queue-local copy
 * of the device flags for smaller cache footprint - better for fast
 * paths.
 */
static inline bool ublk_nosrv_should_queue_io(struct ublk_queue *ubq)
{
	return (ubq->flags & UBLK_F_USER_RECOVERY) &&
	       !(ubq->flags & UBLK_F_USER_RECOVERY_FAIL_IO);
}

/*
 * Should ublk devices be stopped (i.e. no recovery possible) when the
 * ublk server exits? If not, devices can be used again by a future
 * incarnation of a ublk server via the start_recovery/end_recovery
 * commands.
 */
static inline bool ublk_nosrv_should_stop_dev(struct ublk_device *ub)
{
	return !(ub->dev_info.flags & UBLK_F_USER_RECOVERY);
}

static inline bool ublk_dev_in_recoverable_state(struct ublk_device *ub)
{
	return ub->dev_info.state == UBLK_S_DEV_QUIESCED ||
	       ub->dev_info.state == UBLK_S_DEV_FAIL_IO;
}

static void ublk_free_disk(struct gendisk *disk)
{
	struct ublk_device *ub = disk->private_data;

	clear_bit(UB_STATE_USED, &ub->state);
	ublk_put_device(ub);
}

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;
	}

	if (ub->block_open)
		return -ENXIO;

	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,
};

static bool ublk_copy_user_bvec(const struct bio_vec *bv, unsigned *offset,
				struct iov_iter *uiter, int dir, size_t *done)
{
	unsigned len;
	void *bv_buf;
	size_t copied;

	if (*offset >= bv->bv_len) {
		*offset -= bv->bv_len;
		return true;
	}

	len = bv->bv_len - *offset;
	bv_buf = kmap_local_page(bv->bv_page) + bv->bv_offset + *offset;
	if (dir == ITER_DEST)
		copied = copy_to_iter(bv_buf, len, uiter);
	else
		copied = copy_from_iter(bv_buf, len, uiter);

	kunmap_local(bv_buf);

	*done += copied;
	if (copied < len)
		return false;

	*offset = 0;
	return true;
}

/*
 * 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 req_iterator iter;
	struct bio_vec bv;
	size_t done = 0;

	rq_for_each_segment(bv, req, iter) {
		if (!ublk_copy_user_bvec(&bv, &offset, uiter, dir, &done))
			break;
	}
	return done;
}

#ifdef CONFIG_BLK_DEV_INTEGRITY
static size_t ublk_copy_user_integrity(const struct request *req,
		unsigned offset, struct iov_iter *uiter, int dir)
{
	size_t done = 0;
	struct bio *bio = req->bio;
	struct bvec_iter iter;
	struct bio_vec iv;

	if (!blk_integrity_rq(req))
		return 0;

	bio_for_each_integrity_vec(iv, bio, iter) {
		if (!ublk_copy_user_bvec(&iv, &offset, uiter, dir, &done))
			break;
	}

	return done;
}
#else /* #ifdef CONFIG_BLK_DEV_INTEGRITY */
static size_t ublk_copy_user_integrity(const struct request *req,
		unsigned offset, struct iov_iter *uiter, int dir)
{
	return 0;
}
#endif /* #ifdef CONFIG_BLK_DEV_INTEGRITY */

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 unsigned int ublk_map_io(const struct ublk_queue *ubq,
				const struct request *req,
				const struct ublk_io *io)
{
	const unsigned int rq_bytes = blk_rq_bytes(req);

	if (!ublk_need_map_io(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;
		const int dir = ITER_DEST;

		import_ubuf(dir, u64_to_user_ptr(io->buf.addr), rq_bytes, &iter);
		return ublk_copy_user_pages(req, 0, &iter, dir);
	}
	return rq_bytes;
}

static unsigned int ublk_unmap_io(bool need_map,
		const struct request *req,
		const struct ublk_io *io)
{
	const unsigned int rq_bytes = blk_rq_bytes(req);

	if (!need_map)
		return rq_bytes;

	if (ublk_need_unmap_req(req)) {
		struct iov_iter iter;
		const int dir = ITER_SOURCE;

		WARN_ON_ONCE(io->res > rq_bytes);

		import_ubuf(dir, u64_to_user_ptr(io->buf.addr), io->res, &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;

	if (blk_integrity_rq(req))
		flags |= UBLK_IO_F_INTEGRITY;

	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];
	u32 ublk_op;

	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);

	/* Try shmem zero-copy match before setting addr */
	if (ublk_support_shmem_zc(ubq) && ublk_rq_has_data(req)) {
		u32 buf_idx, buf_off;

		if (ublk_try_buf_match(ubq->dev, req,
					  &buf_idx, &buf_off)) {
			iod->op_flags |= UBLK_IO_F_SHMEM_ZC;
			iod->addr = ublk_shmem_zc_addr(buf_idx, buf_off);
			return BLK_STS_OK;
		}
	}

	iod->addr = io->buf.addr;

	return BLK_STS_OK;
}

static inline struct ublk_uring_cmd_pdu *ublk_get_uring_cmd_pdu(
		struct io_uring_cmd *ioucmd)
{
	return io_uring_cmd_to_pdu(ioucmd, struct ublk_uring_cmd_pdu);
}

static void ublk_end_request(struct request *req, blk_status_t error)
{
	local_bh_disable();
	blk_mq_end_request(req, error);
	local_bh_enable();
}

/* todo: handle partial completion */
static inline void __ublk_complete_rq(struct request *req, struct ublk_io *io,
				      bool need_map, struct io_comp_batch *iob)
{
	unsigned int unmapped_bytes;
	blk_status_t res = BLK_STS_OK;
	bool requeue;

	/* 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;

	/* shmem zero copy: no data to unmap, pages already shared */
	if (ublk_iod_is_shmem_zc(req->mq_hctx->driver_data, req->tag))
		goto exit;

	/* for READ request, writing data in iod->addr to rq buffers */
	unmapped_bytes = ublk_unmap_io(need_map, 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;

	/*
	 * Run bio->bi_end_io() with softirqs disabled. If the final fput
	 * happens off this path, then that will prevent ublk's blkdev_release()
	 * from being called on current's task work, see fput() implementation.
	 *
	 * Otherwise, ublk server may not provide forward progress in case of
	 * reading the partition table from bdev_open() with disk->open_mutex
	 * held, and causes dead lock as we could already be holding
	 * disk->open_mutex here.
	 *
	 * Preferably we would not be doing IO with a mutex held that is also
	 * used for release, but this work-around will suffice for now.
	 */
	local_bh_disable();
	requeue = blk_update_request(req, BLK_STS_OK, io->res);
	local_bh_enable();
	if (requeue)
		blk_mq_requeue_request(req, true);
	else if (likely(!blk_should_fake_timeout(req->q))) {
		if (blk_mq_add_to_batch(req, iob, false, blk_mq_end_request_batch))
			return;
		__blk_mq_end_request(req, BLK_STS_OK);
	}

	return;
exit:
	ublk_end_request(req, res);
}

static struct io_uring_cmd *__ublk_prep_compl_io_cmd(struct ublk_io *io,
						     struct request *req)
{
	/* read cmd first because req will overwrite it */
	struct io_uring_cmd *cmd = io->cmd;

	/* 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;

	io->req = req;
	return cmd;
}

static void ublk_complete_io_cmd(struct ublk_io *io, struct request *req,
				 int res, unsigned issue_flags)
{
	struct io_uring_cmd *cmd = __ublk_prep_compl_io_cmd(io, req);

	/* tell ublksrv one io request is coming */
	io_uring_cmd_done(cmd, res, 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_nosrv_dev_should_queue_io(ubq->dev))
		blk_mq_requeue_request(rq, false);
	else
		ublk_end_request(rq, BLK_STS_IOERR);
}

static void
ublk_auto_buf_reg_fallback(const struct ublk_queue *ubq, unsigned tag)
{
	struct ublksrv_io_desc *iod = ublk_get_iod(ubq, tag);

	iod->op_flags |= UBLK_IO_F_NEED_REG_BUF;
}

enum auto_buf_reg_res {
	AUTO_BUF_REG_FAIL,
	AUTO_BUF_REG_FALLBACK,
	AUTO_BUF_REG_OK,
};

/*
 * Setup io state after auto buffer registration.
 *
 * Must be called after ublk_auto_buf_register() is done.
 * Caller must hold io->lock in batch context.
 */
static void ublk_auto_buf_io_setup(const struct ublk_queue *ubq,
				   struct request *req, struct ublk_io *io,
				   struct io_uring_cmd *cmd,
				   enum auto_buf_reg_res res)
{
	if (res == AUTO_BUF_REG_OK) {
		io->task_registered_buffers = 1;
		io->buf_ctx_handle = io_uring_cmd_ctx_handle(cmd);
		io->flags |= UBLK_IO_FLAG_AUTO_BUF_REG;
	}
	ublk_init_req_ref(ubq, io);
	__ublk_prep_compl_io_cmd(io, req);
}

/* Register request bvec to io_uring for auto buffer registration. */
static enum auto_buf_reg_res
ublk_auto_buf_register(const struct ublk_queue *ubq, struct request *req,
		       struct ublk_io *io, struct io_uring_cmd *cmd,
		       unsigned int issue_flags)
{
	int ret;

	ret = io_buffer_register_bvec(cmd, req, ublk_io_release,
				      io->buf.auto_reg.index, issue_flags);
	if (ret) {
		if (io->buf.auto_reg.flags & UBLK_AUTO_BUF_REG_FALLBACK) {
			ublk_auto_buf_reg_fallback(ubq, req->tag);
			return AUTO_BUF_REG_FALLBACK;
		}
		ublk_end_request(req, BLK_STS_IOERR);
		return AUTO_BUF_REG_FAIL;
	}

	return AUTO_BUF_REG_OK;
}

/*
 * Dispatch IO to userspace with auto buffer registration.
 *
 * Only called in non-batch context from task work, io->lock not held.
 */
static void ublk_auto_buf_dispatch(const struct ublk_queue *ubq,
				   struct request *req, struct ublk_io *io,
				   struct io_uring_cmd *cmd,
				   unsigned int issue_flags)
{
	enum auto_buf_reg_res res = ublk_auto_buf_register(ubq, req, io, cmd,
			issue_flags);

	if (res != AUTO_BUF_REG_FAIL) {
		ublk_auto_buf_io_setup(ubq, req, io, cmd, res);
		io_uring_cmd_done(cmd, UBLK_IO_RES_OK, issue_flags);
	}
}

static bool ublk_start_io(const struct ublk_queue *ubq, struct request *req,
			  struct ublk_io *io)
{
	unsigned mapped_bytes;

	/* shmem zero copy: skip data copy, pages already shared */
	if (ublk_iod_is_shmem_zc(ubq, req->tag))
		return true;

	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 false;
		}

		ublk_get_iod(ubq, req->tag)->nr_sectors =
			mapped_bytes >> 9;
	}

	return true;
}

static void ublk_dispatch_req(struct ublk_queue *ubq, struct request *req)
{
	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
	int tag = req->tag;
	struct ublk_io *io = &ubq->ios[tag];

	pr_devel("%s: complete: qid %d tag %d io_flags %x addr %llx\n",
			__func__, ubq->q_id, req->tag, io->flags,
			ublk_get_iod(ubq, req->tag)->addr);

	/*
	 * Task is exiting if either:
	 *
	 * (1) current != io->task.
	 * io_uring_cmd_complete_in_task() tries to run task_work
	 * in a workqueue if cmd's task is PF_EXITING.
	 *
	 * (2) current->flags & PF_EXITING.
	 */
	if (unlikely(current != io->task || 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 immediately pass UBLK_IO_RES_NEED_GET_DATA to ublksrv
		 * and notify it.
		 */
		io->flags |= UBLK_IO_FLAG_NEED_GET_DATA;
		pr_devel("%s: need get data. qid %d tag %d io_flags %x\n",
				__func__, ubq->q_id, req->tag, io->flags);
		ublk_complete_io_cmd(io, req, UBLK_IO_RES_NEED_GET_DATA,
				     issue_flags);
		return;
	}

	if (!ublk_start_io(ubq, req, io))
		return;

	if (ublk_support_auto_buf_reg(ubq) && ublk_rq_has_data(req)) {
		ublk_auto_buf_dispatch(ubq, req, io, io->cmd, issue_flags);
	} else {
		ublk_init_req_ref(ubq, io);
		ublk_complete_io_cmd(io, req, UBLK_IO_RES_OK, issue_flags);
	}
}

static bool __ublk_batch_prep_dispatch(struct ublk_queue *ubq,
				       const struct ublk_batch_io_data *data,
				       unsigned short tag)
{
	struct ublk_device *ub = data->ub;
	struct ublk_io *io = &ubq->ios[tag];
	struct request *req = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], tag);
	enum auto_buf_reg_res res = AUTO_BUF_REG_FALLBACK;
	struct io_uring_cmd *cmd = data->cmd;

	if (!ublk_start_io(ubq, req, io))
		return false;

	if (ublk_support_auto_buf_reg(ubq) && ublk_rq_has_data(req)) {
		res = ublk_auto_buf_register(ubq, req, io, cmd,
				data->issue_flags);

		if (res == AUTO_BUF_REG_FAIL)
			return false;
	}

	ublk_io_lock(io);
	ublk_auto_buf_io_setup(ubq, req, io, cmd, res);
	ublk_io_unlock(io);

	return true;
}

static bool ublk_batch_prep_dispatch(struct ublk_queue *ubq,
				     const struct ublk_batch_io_data *data,
				     unsigned short *tag_buf,
				     unsigned int len)
{
	bool has_unused = false;
	unsigned int i;

	for (i = 0; i < len; i++) {
		unsigned short tag = tag_buf[i];

		if (!__ublk_batch_prep_dispatch(ubq, data, tag)) {
			tag_buf[i] = UBLK_BATCH_IO_UNUSED_TAG;
			has_unused = true;
		}
	}

	return has_unused;
}

/*
 * Filter out UBLK_BATCH_IO_UNUSED_TAG entries from tag_buf.
 * Returns the new length after filtering.
 */
static noinline unsigned int ublk_filter_unused_tags(unsigned short *tag_buf,
					    unsigned int len)
{
	unsigned int i, j;

	for (i = 0, j = 0; i < len; i++) {
		if (tag_buf[i] != UBLK_BATCH_IO_UNUSED_TAG) {
			if (i != j)
				tag_buf[j] = tag_buf[i];
			j++;
		}
	}

	return j;
}

static noinline void ublk_batch_dispatch_fail(struct ublk_queue *ubq,
		const struct ublk_batch_io_data *data,
		unsigned short *tag_buf, size_t len, int ret)
{
	int i, res;

	/*
	 * Undo prep state for all IOs since userspace never received them.
	 * This restores IOs to pre-prepared state so they can be cleanly
	 * re-prepared when tags are pulled from FIFO again.
	 */
	for (i = 0; i < len; i++) {
		struct ublk_io *io = &ubq->ios[tag_buf[i]];
		int index = -1;

		ublk_io_lock(io);
		if (io->flags & UBLK_IO_FLAG_AUTO_BUF_REG)
			index = io->buf.auto_reg.index;
		io->flags &= ~(UBLK_IO_FLAG_OWNED_BY_SRV | UBLK_IO_FLAG_AUTO_BUF_REG);
		io->flags |= UBLK_IO_FLAG_ACTIVE;
		ublk_io_unlock(io);

		if (index != -1)
			io_buffer_unregister_bvec(data->cmd, index,
					data->issue_flags);
	}

	res = kfifo_in_spinlocked_noirqsave(&ubq->evts_fifo,
		tag_buf, len, &ubq->evts_lock);

	pr_warn_ratelimited("%s: copy tags or post CQE failure, move back "
			"tags(%d %zu) ret %d\n", __func__, res, len,
			ret);
}

#define MAX_NR_TAG 128
static int __ublk_batch_dispatch(struct ublk_queue *ubq,
				 const struct ublk_batch_io_data *data,
				 struct ublk_batch_fetch_cmd *fcmd)
{
	const unsigned int tag_sz = sizeof(unsigned short);
	unsigned short tag_buf[MAX_NR_TAG];
	struct io_br_sel sel;
	size_t len = 0;
	bool needs_filter;
	int ret;

	WARN_ON_ONCE(data->cmd != fcmd->cmd);

	sel = io_uring_cmd_buffer_select(fcmd->cmd, fcmd->buf_group, &len,
					 data->issue_flags);
	if (sel.val < 0)
		return sel.val;
	if (!sel.addr)
		return -ENOBUFS;

	/* single reader needn't lock and sizeof(kfifo element) is 2 bytes */
	len = min(len, sizeof(tag_buf)) / tag_sz;
	len = kfifo_out(&ubq->evts_fifo, tag_buf, len);

	needs_filter = ublk_batch_prep_dispatch(ubq, data, tag_buf, len);
	/* Filter out unused tags before posting to userspace */
	if (unlikely(needs_filter)) {
		int new_len = ublk_filter_unused_tags(tag_buf, len);

		/* return actual length if all are failed or requeued */
		if (!new_len) {
			/* release the selected buffer */
			sel.val = 0;
			WARN_ON_ONCE(!io_uring_mshot_cmd_post_cqe(fcmd->cmd,
						&sel, data->issue_flags));
			return len;
		}
		len = new_len;
	}

	sel.val = ublk_batch_copy_io_tags(fcmd, sel.addr, tag_buf, len * tag_sz);
	ret = ublk_batch_fetch_post_cqe(fcmd, &sel, data->issue_flags);
	if (unlikely(ret < 0))
		ublk_batch_dispatch_fail(ubq, data, tag_buf, len, ret);
	return ret;
}

static struct ublk_batch_fetch_cmd *__ublk_acquire_fcmd(
		struct ublk_queue *ubq)
{
	struct ublk_batch_fetch_cmd *fcmd;

	lockdep_assert_held(&ubq->evts_lock);

	/*
	 * Ordering updating ubq->evts_fifo and checking ubq->active_fcmd.
	 *
	 * The pair is the smp_mb() in ublk_batch_dispatch().
	 *
	 * If ubq->active_fcmd is observed as non-NULL, the new added tags
	 * can be visisible in ublk_batch_dispatch() with the barrier pairing.
	 */
	smp_mb();
	if (READ_ONCE(ubq->active_fcmd)) {
		fcmd = NULL;
	} else {
		fcmd = list_first_entry_or_null(&ubq->fcmd_head,
				struct ublk_batch_fetch_cmd, node);
		WRITE_ONCE(ubq->active_fcmd, fcmd);
	}
	return fcmd;
}

static void ublk_batch_tw_cb(struct io_tw_req tw_req, io_tw_token_t tw)
{
	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
	struct ublk_batch_fetch_cmd *fcmd = pdu->fcmd;
	struct ublk_batch_io_data data = {
		.ub = pdu->ubq->dev,
		.cmd = fcmd->cmd,
		.issue_flags = issue_flags,
	};

	WARN_ON_ONCE(pdu->ubq->active_fcmd != fcmd);

	ublk_batch_dispatch(pdu->ubq, &data, fcmd);
}

static void
ublk_batch_dispatch(struct ublk_queue *ubq,
		    const struct ublk_batch_io_data *data,
		    struct ublk_batch_fetch_cmd *fcmd)
{
	struct ublk_batch_fetch_cmd *new_fcmd;
	unsigned tried = 0;
	int ret = 0;

again:
	while (!ublk_io_evts_empty(ubq)) {
		ret = __ublk_batch_dispatch(ubq, data, fcmd);
		if (ret <= 0)
			break;
	}

	if (ret < 0) {
		ublk_batch_deinit_fetch_buf(ubq, data, fcmd, ret);
		return;
	}

	__ublk_release_fcmd(ubq);
	/*
	 * Order clearing ubq->active_fcmd from __ublk_release_fcmd() and
	 * checking ubq->evts_fifo.
	 *
	 * The pair is the smp_mb() in __ublk_acquire_fcmd().
	 */
	smp_mb();
	if (likely(ublk_io_evts_empty(ubq)))
		return;

	spin_lock(&ubq->evts_lock);
	new_fcmd = __ublk_acquire_fcmd(ubq);
	spin_unlock(&ubq->evts_lock);

	if (!new_fcmd)
		return;

	/* Avoid lockup by allowing to handle at most 32 batches */
	if (new_fcmd == fcmd && tried++ < 32)
		goto again;

	io_uring_cmd_complete_in_task(new_fcmd->cmd, ublk_batch_tw_cb);
}

static void ublk_cmd_tw_cb(struct io_tw_req tw_req, io_tw_token_t tw)
{
	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
	struct ublk_queue *ubq = pdu->ubq;

	ublk_dispatch_req(ubq, pdu->req);
}

static void ublk_batch_queue_cmd(struct ublk_queue *ubq, struct request *rq, bool last)
{
	unsigned short tag = rq->tag;
	struct ublk_batch_fetch_cmd *fcmd = NULL;

	spin_lock(&ubq->evts_lock);
	kfifo_put(&ubq->evts_fifo, tag);
	if (last)
		fcmd = __ublk_acquire_fcmd(ubq);
	spin_unlock(&ubq->evts_lock);

	if (fcmd)
		io_uring_cmd_complete_in_task(fcmd->cmd, ublk_batch_tw_cb);
}

static void ublk_queue_cmd(struct ublk_queue *ubq, struct request *rq)
{
	struct io_uring_cmd *cmd = ubq->ios[rq->tag].cmd;
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);

	pdu->req = rq;
	io_uring_cmd_complete_in_task(cmd, ublk_cmd_tw_cb);
}

static void ublk_cmd_list_tw_cb(struct io_tw_req tw_req, io_tw_token_t tw)
{
	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
	struct request *rq = pdu->req_list;
	struct request *next;

	do {
		next = rq->rq_next;
		rq->rq_next = NULL;
		ublk_dispatch_req(rq->mq_hctx->driver_data, rq);
		rq = next;
	} while (rq);
}

static void ublk_queue_cmd_list(struct ublk_io *io, struct rq_list *l)
{
	struct io_uring_cmd *cmd = io->cmd;
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);

	pdu->req_list = rq_list_peek(l);
	rq_list_init(l);
	io_uring_cmd_complete_in_task(cmd, ublk_cmd_list_tw_cb);
}

static enum blk_eh_timer_return ublk_timeout(struct request *rq)
{
	struct ublk_queue *ubq = rq->mq_hctx->driver_data;
	pid_t tgid = ubq->dev->ublksrv_tgid;
	struct task_struct *p;
	struct pid *pid;

	if (!(ubq->flags & UBLK_F_UNPRIVILEGED_DEV))
		return BLK_EH_RESET_TIMER;

	if (unlikely(!tgid))
		return BLK_EH_RESET_TIMER;

	rcu_read_lock();
	pid = find_vpid(tgid);
	p = pid_task(pid, PIDTYPE_PID);
	if (p)
		send_sig(SIGKILL, p, 0);
	rcu_read_unlock();
	return BLK_EH_DONE;
}

static blk_status_t ublk_prep_req(struct ublk_queue *ubq, struct request *rq,
				  bool check_cancel)
{
	blk_status_t res;

	if (unlikely(READ_ONCE(ubq->fail_io)))
		return BLK_STS_TARGET;

	/* 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_nosrv_should_queue_io(ubq) &&
	    unlikely(READ_ONCE(ubq->force_abort)))
		return BLK_STS_IOERR;

	if (check_cancel && unlikely(ubq->canceling))
		return BLK_STS_IOERR;

	/* fill iod to slot in io cmd buffer */
	res = ublk_setup_iod(ubq, rq);
	if (unlikely(res != BLK_STS_OK))
		return BLK_STS_IOERR;

	blk_mq_start_request(rq);
	return BLK_STS_OK;
}

/*
 * Common helper for queue_rq that handles request preparation and
 * cancellation checks. Returns status and sets should_queue to indicate
 * whether the caller should proceed with queuing the request.
 */
static inline blk_status_t __ublk_queue_rq_common(struct ublk_queue *ubq,
						   struct request *rq,
						   bool *should_queue)
{
	blk_status_t res;

	res = ublk_prep_req(ubq, rq, false);
	if (res != BLK_STS_OK) {
		*should_queue = false;
		return res;
	}

	/*
	 * ->canceling has to be handled after ->force_abort and ->fail_io
	 * is dealt with, otherwise this request may not be failed in case
	 * of recovery, and cause hang when deleting disk
	 */
	if (unlikely(ubq->canceling)) {
		*should_queue = false;
		__ublk_abort_rq(ubq, rq);
		return BLK_STS_OK;
	}

	*should_queue = true;
	return BLK_STS_OK;
}

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;
	bool should_queue;
	blk_status_t res;

	res = __ublk_queue_rq_common(ubq, rq, &should_queue);
	if (!should_queue)
		return res;

	ublk_queue_cmd(ubq, rq);
	return BLK_STS_OK;
}

static blk_status_t ublk_batch_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;
	bool should_queue;
	blk_status_t res;

	res = __ublk_queue_rq_common(ubq, rq, &should_queue);
	if (!should_queue)
		return res;

	ublk_batch_queue_cmd(ubq, rq, bd->last);
	return BLK_STS_OK;
}

static inline bool ublk_belong_to_same_batch(const struct ublk_io *io,
					     const struct ublk_io *io2)
{
	return (io_uring_cmd_ctx_handle(io->cmd) ==
		io_uring_cmd_ctx_handle(io2->cmd)) &&
		(io->task == io2->task);
}

static void ublk_commit_rqs(struct blk_mq_hw_ctx *hctx)
{
	struct ublk_queue *ubq = hctx->driver_data;
	struct ublk_batch_fetch_cmd *fcmd;

	spin_lock(&ubq->evts_lock);
	fcmd = __ublk_acquire_fcmd(ubq);
	spin_unlock(&ubq->evts_lock);

	if (fcmd)
		io_uring_cmd_complete_in_task(fcmd->cmd, ublk_batch_tw_cb);
}

static void ublk_queue_rqs(struct rq_list *rqlist)
{
	struct rq_list requeue_list = { };
	struct rq_list submit_list = { };
	struct ublk_io *io = NULL;
	struct request *req;

	while ((req = rq_list_pop(rqlist))) {
		struct ublk_queue *this_q = req->mq_hctx->driver_data;
		struct ublk_io *this_io = &this_q->ios[req->tag];

		if (ublk_prep_req(this_q, req, true) != BLK_STS_OK) {
			rq_list_add_tail(&requeue_list, req);
			continue;
		}

		if (io && !ublk_belong_to_same_batch(io, this_io) &&
				!rq_list_empty(&submit_list))
			ublk_queue_cmd_list(io, &submit_list);
		io = this_io;
		rq_list_add_tail(&submit_list, req);
	}

	if (!rq_list_empty(&submit_list))
		ublk_queue_cmd_list(io, &submit_list);
	*rqlist = requeue_list;
}

static void ublk_batch_queue_cmd_list(struct ublk_queue *ubq, struct rq_list *l)
{
	unsigned short tags[MAX_NR_TAG];
	struct ublk_batch_fetch_cmd *fcmd;
	struct request *rq;
	unsigned cnt = 0;

	spin_lock(&ubq->evts_lock);
	rq_list_for_each(l, rq) {
		tags[cnt++] = (unsigned short)rq->tag;
		if (cnt >= MAX_NR_TAG) {
			kfifo_in(&ubq->evts_fifo, tags, cnt);
			cnt = 0;
		}
	}
	if (cnt)
		kfifo_in(&ubq->evts_fifo, tags, cnt);
	fcmd = __ublk_acquire_fcmd(ubq);
	spin_unlock(&ubq->evts_lock);

	rq_list_init(l);
	if (fcmd)
		io_uring_cmd_complete_in_task(fcmd->cmd, ublk_batch_tw_cb);
}

static void ublk_batch_queue_rqs(struct rq_list *rqlist)
{
	struct rq_list requeue_list = { };
	struct rq_list submit_list = { };
	struct ublk_queue *ubq = NULL;
	struct request *req;

	while ((req = rq_list_pop(rqlist))) {
		struct ublk_queue *this_q = req->mq_hctx->driver_data;

		if (ublk_prep_req(this_q, req, true) != BLK_STS_OK) {
			rq_list_add_tail(&requeue_list, req);
			continue;
		}

		if (ubq && this_q != ubq && !rq_list_empty(&submit_list))
			ublk_batch_queue_cmd_list(ubq, &submit_list);
		ubq = this_q;
		rq_list_add_tail(&submit_list, req);
	}

	if (!rq_list_empty(&submit_list))
		ublk_batch_queue_cmd_list(ubq, &submit_list);
	*rqlist = requeue_list;
}

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,
	.queue_rqs      = ublk_queue_rqs,
	.init_hctx	= ublk_init_hctx,
	.timeout	= ublk_timeout,
};

static const struct blk_mq_ops ublk_batch_mq_ops = {
	.commit_rqs	= ublk_commit_rqs,
	.queue_rq       = ublk_batch_queue_rq,
	.queue_rqs      = ublk_batch_queue_rqs,
	.init_hctx	= ublk_init_hctx,
	.timeout	= ublk_timeout,
};

static void ublk_queue_reinit(struct ublk_device *ub, struct ublk_queue *ubq)
{
	int i;

	ubq->nr_io_ready = 0;

	for (i = 0; i < ubq->q_depth; i++) {
		struct ublk_io *io = &ubq->ios[i];

		/*
		 * UBLK_IO_FLAG_CANCELED is kept for avoiding to touch
		 * io->cmd
		 */
		io->flags &= UBLK_IO_FLAG_CANCELED;
		io->cmd = NULL;
		io->buf.addr = 0;

		/*
		 * old task is PF_EXITING, put it now
		 *
		 * It could be NULL in case of closing one quiesced
		 * device.
		 */
		if (io->task) {
			put_task_struct(io->task);
			io->task = NULL;
		}

		WARN_ON_ONCE(refcount_read(&io->ref));
		WARN_ON_ONCE(io->task_registered_buffers);
	}
}

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;
	ub->ublksrv_tgid = current->tgid;
	return 0;
}

static void ublk_reset_ch_dev(struct ublk_device *ub)
{
	int i;

	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 tasks cannot mmap io_cmd_buf */
	ub->mm = NULL;
	ub->nr_queue_ready = 0;
	ub->unprivileged_daemons = false;
	ub->ublksrv_tgid = -1;
}

static struct gendisk *ublk_get_disk(struct ublk_device *ub)
{
	struct gendisk *disk;

	spin_lock(&ub->lock);
	disk = ub->ub_disk;
	if (disk)
		get_device(disk_to_dev(disk));
	spin_unlock(&ub->lock);

	return disk;
}

static void ublk_put_disk(struct gendisk *disk)
{
	if (disk)
		put_device(disk_to_dev(disk));
}

static void ublk_partition_scan_work(struct work_struct *work)
{
	struct ublk_device *ub =
		container_of(work, struct ublk_device, partition_scan_work);
	/* Hold disk reference to prevent UAF during concurrent teardown */
	struct gendisk *disk = ublk_get_disk(ub);

	if (!disk)
		return;

	if (WARN_ON_ONCE(!test_and_clear_bit(GD_SUPPRESS_PART_SCAN,
					     &disk->state)))
		goto out;

	mutex_lock(&disk->open_mutex);
	bdev_disk_changed(disk, false);
	mutex_unlock(&disk->open_mutex);
out:
	ublk_put_disk(disk);
}

/*
 * Use this function to ensure that ->canceling is consistently set for
 * the device and all queues. Do not set these flags directly.
 *
 * Caller must ensure that:
 * - cancel_mutex is held. This ensures that there is no concurrent
 *   access to ub->canceling and no concurrent writes to ubq->canceling.
 * - there are no concurrent reads of ubq->canceling from the queue_rq
 *   path. This can be done by quiescing the queue, or through other
 *   means.
 */
static void ublk_set_canceling(struct ublk_device *ub, bool canceling)
	__must_hold(&ub->cancel_mutex)
{
	int i;

	ub->canceling = canceling;
	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
		ublk_get_queue(ub, i)->canceling = canceling;
}

static bool ublk_check_and_reset_active_ref(struct ublk_device *ub)
{
	int i, j;

	if (!ublk_dev_need_req_ref(ub))
		return false;

	for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
		struct ublk_queue *ubq = ublk_get_queue(ub, i);

		for (j = 0; j < ubq->q_depth; j++) {
			struct ublk_io *io = &ubq->ios[j];
			unsigned int refs = refcount_read(&io->ref) +
				io->task_registered_buffers;

			/*
			 * UBLK_REFCOUNT_INIT or zero means no active
			 * reference
			 */
			if (refs != UBLK_REFCOUNT_INIT && refs != 0)
				return true;

			/* reset to zero if the io hasn't active references */
			refcount_set(&io->ref, 0);
			io->task_registered_buffers = 0;
		}
	}
	return false;
}

static void ublk_ch_release_work_fn(struct work_struct *work)
{
	struct ublk_device *ub =
		container_of(work, struct ublk_device, exit_work.work);
	struct gendisk *disk;
	int i;

	/*
	 * For zero-copy and auto buffer register modes, I/O references
	 * might not be dropped naturally when the daemon is killed, but
	 * io_uring guarantees that registered bvec kernel buffers are
	 * unregistered finally when freeing io_uring context, then the
	 * active references are dropped.
	 *
	 * Wait until active references are dropped for avoiding use-after-free
	 *
	 * registered buffer may be unregistered in io_ring's release hander,
	 * so have to wait by scheduling work function for avoiding the two
	 * file release dependency.
	 */
	if (ublk_check_and_reset_active_ref(ub)) {
		schedule_delayed_work(&ub->exit_work, 1);
		return;
	}

	/*
	 * disk isn't attached yet, either device isn't live, or it has
	 * been removed already, so we needn't to do anything
	 */
	disk = ublk_get_disk(ub);
	if (!disk)
		goto out;

	/*
	 * All uring_cmd are done now, so abort any request outstanding to
	 * the ublk server
	 *
	 * This can be done in lockless way because ublk server has been
	 * gone
	 *
	 * More importantly, we have to provide forward progress guarantee
	 * without holding ub->mutex, otherwise control task grabbing
	 * ub->mutex triggers deadlock
	 *
	 * All requests may be inflight, so ->canceling may not be set, set
	 * it now.
	 */
	mutex_lock(&ub->cancel_mutex);
	ublk_set_canceling(ub, true);
	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
		ublk_abort_queue(ub, ublk_get_queue(ub, i));
	mutex_unlock(&ub->cancel_mutex);
	blk_mq_kick_requeue_list(disk->queue);

	/*
	 * All infligh requests have been completed or requeued and any new
	 * request will be failed or requeued via `->canceling` now, so it is
	 * fine to grab ub->mutex now.
	 */
	mutex_lock(&ub->mutex);

	/* double check after grabbing lock */
	if (!ub->ub_disk)
		goto unlock;

	/*
	 * Transition the device to the nosrv state. What exactly this
	 * means depends on the recovery flags
	 */
	if (ublk_nosrv_should_stop_dev(ub)) {
		/*
		 * Allow any pending/future I/O to pass through quickly
		 * with an error. This is needed because del_gendisk
		 * waits for all pending I/O to complete
		 */
		for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
			WRITE_ONCE(ublk_get_queue(ub, i)->force_abort, true);

		ublk_stop_dev_unlocked(ub);
	} else {
		if (ublk_nosrv_dev_should_queue_io(ub)) {
			/* ->canceling is set and all requests are aborted */
			ub->dev_info.state = UBLK_S_DEV_QUIESCED;
		} else {
			ub->dev_info.state = UBLK_S_DEV_FAIL_IO;
			for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
				WRITE_ONCE(ublk_get_queue(ub, i)->fail_io, true);
		}
	}
unlock:
	mutex_unlock(&ub->mutex);
	ublk_put_disk(disk);

	/* all uring_cmd has been done now, reset device & ubq */
	ublk_reset_ch_dev(ub);
out:
	clear_bit(UB_STATE_OPEN, &ub->state);

	/* put the reference grabbed in ublk_ch_release() */
	ublk_put_device(ub);
}

static int ublk_ch_release(struct inode *inode, struct file *filp)
{
	struct ublk_device *ub = filp->private_data;

	/*
	 * Grab ublk device reference, so it won't be gone until we are
	 * really released from work function.
	 */
	ublk_get_device(ub);

	INIT_DELAYED_WORK(&ub->exit_work, ublk_ch_release_work_fn);
	schedule_delayed_work(&ub->exit_work, 0);
	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_cmd_buf_size();
	unsigned long pfn, end, phys_off = vma->vm_pgoff << PAGE_SHIFT;
	int q_id, ret = 0;

	spin_lock(&ub->lock);
	if (!ub->mm)
		ub->mm = current->mm;
	if (current->mm != ub->mm)
		ret = -EINVAL;
	spin_unlock(&ub->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))
		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_fail_req(struct ublk_device *ub, struct ublk_io *io,
		struct request *req)
{
	WARN_ON_ONCE(!ublk_dev_support_batch_io(ub) &&
			io->flags & UBLK_IO_FLAG_ACTIVE);

	if (ublk_nosrv_should_reissue_outstanding(ub))
		blk_mq_requeue_request(req, false);
	else {
		io->res = -EIO;
		__ublk_complete_rq(req, io, ublk_dev_need_map_io(ub), NULL);
	}
}

/*
 * Request tag may just be filled to event kfifo, not get chance to
 * dispatch, abort these requests too
 */
static void ublk_abort_batch_queue(struct ublk_device *ub,
				   struct ublk_queue *ubq)
{
	unsigned short tag;

	while (kfifo_out(&ubq->evts_fifo, &tag, 1)) {
		struct request *req = blk_mq_tag_to_rq(
				ub->tag_set.tags[ubq->q_id], tag);

		if (!WARN_ON_ONCE(!req || !blk_mq_request_started(req)))
			__ublk_fail_req(ub, &ubq->ios[tag], req);
	}
}

/*
 * Called from ublk char device release handler, when any uring_cmd is
 * done, meantime request queue is "quiesced" since all inflight requests
 * can't be completed because ublk server is dead.
 *
 * So no one can hold our request IO reference any more, simply ignore the
 * reference, and complete the request immediately
 */
static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq)
{
	int i;

	for (i = 0; i < ubq->q_depth; i++) {
		struct ublk_io *io = &ubq->ios[i];

		if (io->flags & UBLK_IO_FLAG_OWNED_BY_SRV)
			__ublk_fail_req(ub, io, io->req);
	}

	if (ublk_support_batch_io(ubq))
		ublk_abort_batch_queue(ub, ubq);
}

static void ublk_start_cancel(struct ublk_device *ub)
{
	struct gendisk *disk = ublk_get_disk(ub);

	/* Our disk has been dead */
	if (!disk)
		return;

	mutex_lock(&ub->cancel_mutex);
	if (ub->canceling)
		goto out;
	/*
	 * Now we are serialized with ublk_queue_rq()
	 *
	 * Make sure that ubq->canceling is set when queue is frozen,
	 * because ublk_queue_rq() has to rely on this flag for avoiding to
	 * touch completed uring_cmd
	 */
	blk_mq_quiesce_queue(disk->queue);
	ublk_set_canceling(ub, true);
	blk_mq_unquiesce_queue(disk->queue);
out:
	mutex_unlock(&ub->cancel_mutex);
	ublk_put_disk(disk);
}

static void ublk_cancel_cmd(struct ublk_queue *ubq, unsigned tag,
		unsigned int issue_flags)
{
	struct ublk_io *io = &ubq->ios[tag];
	struct ublk_device *ub = ubq->dev;
	struct request *req;
	bool done;

	if (!(io->flags & UBLK_IO_FLAG_ACTIVE))
		return;

	/*
	 * Don't try to cancel this command if the request is started for
	 * avoiding race between io_uring_cmd_done() and
	 * io_uring_cmd_complete_in_task().
	 *
	 * Either the started request will be aborted via __ublk_abort_rq(),
	 * then this uring_cmd is canceled next time, or it will be done in
	 * task work function ublk_dispatch_req() because io_uring guarantees
	 * that ublk_dispatch_req() is always called
	 */
	req = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], tag);
	if (req && blk_mq_request_started(req) && req->tag == tag)
		return;

	spin_lock(&ubq->cancel_lock);
	done = !!(io->flags & UBLK_IO_FLAG_CANCELED);
	if (!done)
		io->flags |= UBLK_IO_FLAG_CANCELED;
	spin_unlock(&ubq->cancel_lock);

	if (!done)
		io_uring_cmd_done(io->cmd, UBLK_IO_RES_ABORT, issue_flags);
}

/*
 * Cancel a batch fetch command if it hasn't been claimed by another path.
 *
 * An fcmd can only be cancelled if:
 * 1. It's not the active_fcmd (which is currently being processed)
 * 2. It's still on the list (!list_empty check) - once removed from the list,
 *    the fcmd is considered claimed and will be freed by whoever removed it
 *
 * Use list_del_init() so subsequent list_empty() checks work correctly.
 */
static void ublk_batch_cancel_cmd(struct ublk_queue *ubq,
				  struct ublk_batch_fetch_cmd *fcmd,
				  unsigned int issue_flags)
{
	bool done;

	spin_lock(&ubq->evts_lock);
	done = (READ_ONCE(ubq->active_fcmd) != fcmd) && !list_empty(&fcmd->node);
	if (done)
		list_del_init(&fcmd->node);
	spin_unlock(&ubq->evts_lock);

	if (done) {
		io_uring_cmd_done(fcmd->cmd, UBLK_IO_RES_ABORT, issue_flags);
		ublk_batch_free_fcmd(fcmd);
	}
}

static void ublk_batch_cancel_queue(struct ublk_queue *ubq)
{
	struct ublk_batch_fetch_cmd *fcmd;
	LIST_HEAD(fcmd_list);

	spin_lock(&ubq->evts_lock);
	ubq->force_abort = true;
	list_splice_init(&ubq->fcmd_head, &fcmd_list);
	fcmd = READ_ONCE(ubq->active_fcmd);
	if (fcmd)
		list_move(&fcmd->node, &ubq->fcmd_head);
	spin_unlock(&ubq->evts_lock);

	while (!list_empty(&fcmd_list)) {
		fcmd = list_first_entry(&fcmd_list,
				struct ublk_batch_fetch_cmd, node);
		ublk_batch_cancel_cmd(ubq, fcmd, IO_URING_F_UNLOCKED);
	}
}

static void ublk_batch_cancel_fn(struct io_uring_cmd *cmd,
				 unsigned int issue_flags)
{
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
	struct ublk_batch_fetch_cmd *fcmd = pdu->fcmd;
	struct ublk_queue *ubq = pdu->ubq;

	ublk_start_cancel(ubq->dev);

	ublk_batch_cancel_cmd(ubq, fcmd, issue_flags);
}

/*
 * The ublk char device won't be closed when calling cancel fn, so both
 * ublk device and queue are guaranteed to be live
 *
 * Two-stage cancel:
 *
 * - make every active uring_cmd done in ->cancel_fn()
 *
 * - aborting inflight ublk IO requests in ublk char device release handler,
 *   which depends on 1st stage because device can only be closed iff all
 *   uring_cmd are done
 *
 * Do _not_ try to acquire ub->mutex before all inflight requests are
 * aborted, otherwise deadlock may be caused.
 */
static void ublk_uring_cmd_cancel_fn(struct io_uring_cmd *cmd,
		unsigned int issue_flags)
{
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
	struct ublk_queue *ubq = pdu->ubq;
	struct task_struct *task;
	struct ublk_io *io;

	if (WARN_ON_ONCE(!ubq))
		return;

	if (WARN_ON_ONCE(pdu->tag >= ubq->q_depth))
		return;

	task = io_uring_cmd_get_task(cmd);
	io = &ubq->ios[pdu->tag];
	if (WARN_ON_ONCE(task && task != io->task))
		return;

	ublk_start_cancel(ubq->dev);

	WARN_ON_ONCE(io->cmd != cmd);
	ublk_cancel_cmd(ubq, pdu->tag, issue_flags);
}

static inline bool ublk_queue_ready(const struct ublk_queue *ubq)
{
	return ubq->nr_io_ready == ubq->q_depth;
}

static inline bool ublk_dev_ready(const struct ublk_device *ub)
{
	return ub->nr_queue_ready == ub->dev_info.nr_hw_queues;
}

static void ublk_cancel_queue(struct ublk_queue *ubq)
{
	int i;

	if (ublk_support_batch_io(ubq)) {
		ublk_batch_cancel_queue(ubq);
		return;
	}

	for (i = 0; i < ubq->q_depth; i++)
		ublk_cancel_cmd(ubq, i, IO_URING_F_UNLOCKED);
}

/* 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_force_abort_dev(struct ublk_device *ub)
{
	int i;

	pr_devel("%s: force abort 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);
	if (ub->dev_info.state == UBLK_S_DEV_LIVE)
		ublk_wait_tagset_rqs_idle(ub);

	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 struct gendisk *ublk_detach_disk(struct ublk_device *ub)
{
	struct gendisk *disk;

	/* Sync with ublk_abort_queue() by holding the lock */
	spin_lock(&ub->lock);
	disk = ub->ub_disk;
	ub->dev_info.state = UBLK_S_DEV_DEAD;
	ub->dev_info.ublksrv_pid = -1;
	ub->ub_disk = NULL;
	spin_unlock(&ub->lock);

	return disk;
}

static void ublk_stop_dev_unlocked(struct ublk_device *ub)
	__must_hold(&ub->mutex)
{
	struct gendisk *disk;

	if (ub->dev_info.state == UBLK_S_DEV_DEAD)
		return;

	if (ublk_nosrv_dev_should_queue_io(ub))
		ublk_force_abort_dev(ub);
	del_gendisk(ub->ub_disk);
	disk = ublk_detach_disk(ub);
	put_disk(disk);
}

static void ublk_stop_dev(struct ublk_device *ub)
{
	mutex_lock(&ub->mutex);
	ublk_stop_dev_unlocked(ub);
	mutex_unlock(&ub->mutex);
	cancel_work_sync(&ub->partition_scan_work);
	ublk_cancel_dev(ub);
}

static void ublk_reset_io_flags(struct ublk_queue *ubq, struct ublk_io *io)
{
	/* UBLK_IO_FLAG_CANCELED can be cleared now */
	spin_lock(&ubq->cancel_lock);
	io->flags &= ~UBLK_IO_FLAG_CANCELED;
	spin_unlock(&ubq->cancel_lock);
}

/* reset per-queue io flags */
static void ublk_queue_reset_io_flags(struct ublk_queue *ubq)
{
	spin_lock(&ubq->cancel_lock);
	ubq->canceling = false;
	spin_unlock(&ubq->cancel_lock);
	ubq->fail_io = false;
}

/* device can only be started after all IOs are ready */
static void ublk_mark_io_ready(struct ublk_device *ub, u16 q_id,
	struct ublk_io *io)
	__must_hold(&ub->mutex)
{
	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);

	if (!ub->unprivileged_daemons && !capable(CAP_SYS_ADMIN))
		ub->unprivileged_daemons = true;

	ubq->nr_io_ready++;
	ublk_reset_io_flags(ubq, io);

	/* Check if this specific queue is now fully ready */
	if (ublk_queue_ready(ubq)) {
		ub->nr_queue_ready++;

		/*
		 * Reset queue flags as soon as this queue is ready.
		 * This clears the canceling flag, allowing batch FETCH commands
		 * to succeed during recovery without waiting for all queues.
		 */
		ublk_queue_reset_io_flags(ubq);
	}

	/* Check if all queues are ready */
	if (ublk_dev_ready(ub)) {
		/*
		 * All queues ready - clear device-level canceling flag
		 * and complete the recovery/initialization.
		 */
		mutex_lock(&ub->cancel_mutex);
		ub->canceling = false;
		mutex_unlock(&ub->cancel_mutex);
		complete_all(&ub->completion);
	}
}

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 int ublk_set_auto_buf_reg(struct ublk_io *io, struct io_uring_cmd *cmd)
{
	struct ublk_auto_buf_reg buf;

	buf = ublk_sqe_addr_to_auto_buf_reg(READ_ONCE(cmd->sqe->addr));

	if (buf.reserved0 || buf.reserved1)
		return -EINVAL;

	if (buf.flags & ~UBLK_AUTO_BUF_REG_F_MASK)
		return -EINVAL;
	io->buf.auto_reg = buf;
	return 0;
}

static void ublk_clear_auto_buf_reg(struct ublk_io *io,
				    struct io_uring_cmd *cmd,
				    u16 *buf_idx)
{
	if (io->flags & UBLK_IO_FLAG_AUTO_BUF_REG) {
		io->flags &= ~UBLK_IO_FLAG_AUTO_BUF_REG;

		/*
		 * `UBLK_F_AUTO_BUF_REG` only works iff `UBLK_IO_FETCH_REQ`
		 * and `UBLK_IO_COMMIT_AND_FETCH_REQ` are issued from same
		 * `io_ring_ctx`.
		 *
		 * If this uring_cmd's io_ring_ctx isn't same with the
		 * one for registering the buffer, it is ublk server's
		 * responsibility for unregistering the buffer, otherwise
		 * this ublk request gets stuck.
		 */
		if (io->buf_ctx_handle == io_uring_cmd_ctx_handle(cmd))
			*buf_idx = io->buf.auto_reg.index;
	}
}

static int ublk_handle_auto_buf_reg(struct ublk_io *io,
				    struct io_uring_cmd *cmd,
				    u16 *buf_idx)
{
	ublk_clear_auto_buf_reg(io, cmd, buf_idx);
	return ublk_set_auto_buf_reg(io, cmd);
}

/* Once we return, `io->req` can't be used any more */
static inline struct request *
ublk_fill_io_cmd(struct ublk_io *io, struct io_uring_cmd *cmd)
{
	struct request *req = io->req;

	io->cmd = cmd;
	io->flags |= UBLK_IO_FLAG_ACTIVE;
	/* now this cmd slot is owned by ublk driver */
	io->flags &= ~UBLK_IO_FLAG_OWNED_BY_SRV;

	return req;
}

static inline int
ublk_config_io_buf(const struct ublk_device *ub, struct ublk_io *io,
		   struct io_uring_cmd *cmd, unsigned long buf_addr,
		   u16 *buf_idx)
{
	if (ublk_dev_support_auto_buf_reg(ub))
		return ublk_handle_auto_buf_reg(io, cmd, buf_idx);

	io->buf.addr = buf_addr;
	return 0;
}

static inline void ublk_prep_cancel(struct io_uring_cmd *cmd,
				    unsigned int issue_flags,
				    struct ublk_queue *ubq, unsigned int tag)
{
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);

	/*
	 * Safe to refer to @ubq since ublk_queue won't be died until its
	 * commands are completed
	 */
	pdu->ubq = ubq;
	pdu->tag = tag;
	io_uring_cmd_mark_cancelable(cmd, issue_flags);
}

static void ublk_io_release(void *priv)
{
	struct request *rq = priv;
	struct ublk_queue *ubq = rq->mq_hctx->driver_data;
	struct ublk_io *io = &ubq->ios[rq->tag];

	/*
	 * task_registered_buffers may be 0 if buffers were registered off task
	 * but unregistered on task. Or after UBLK_IO_COMMIT_AND_FETCH_REQ.
	 */
	if (current == io->task && io->task_registered_buffers)
		io->task_registered_buffers--;
	else
		ublk_put_req_ref(io, rq);
}

static int ublk_register_io_buf(struct io_uring_cmd *cmd,
				struct ublk_device *ub,
				u16 q_id, u16 tag,
				struct ublk_io *io,
				unsigned int index, unsigned int issue_flags)
{
	struct request *req;
	int ret;

	if (!ublk_dev_support_zero_copy(ub))
		return -EINVAL;

	req = __ublk_check_and_get_req(ub, q_id, tag, io);
	if (!req)
		return -EINVAL;

	ret = io_buffer_register_bvec(cmd, req, ublk_io_release, index,
				      issue_flags);
	if (ret) {
		ublk_put_req_ref(io, req);
		return ret;
	}

	return 0;
}

static int
ublk_daemon_register_io_buf(struct io_uring_cmd *cmd,
			    struct ublk_device *ub,
			    u16 q_id, u16 tag, struct ublk_io *io,
			    unsigned index, unsigned issue_flags)
{
	unsigned new_registered_buffers;
	struct request *req = io->req;
	int ret;

	/*
	 * Ensure there are still references for ublk_sub_req_ref() to release.
	 * If not, fall back on the thread-safe buffer registration.
	 */
	new_registered_buffers = io->task_registered_buffers + 1;
	if (unlikely(new_registered_buffers >= UBLK_REFCOUNT_INIT))
		return ublk_register_io_buf(cmd, ub, q_id, tag, io, index,
					    issue_flags);

	if (!ublk_dev_support_zero_copy(ub) || !ublk_rq_has_data(req))
		return -EINVAL;

	ret = io_buffer_register_bvec(cmd, req, ublk_io_release, index,
				      issue_flags);
	if (ret)
		return ret;

	io->task_registered_buffers = new_registered_buffers;
	return 0;
}

static int ublk_unregister_io_buf(struct io_uring_cmd *cmd,
				  const struct ublk_device *ub,
				  unsigned int index, unsigned int issue_flags)
{
	if (!(ub->dev_info.flags & UBLK_F_SUPPORT_ZERO_COPY))
		return -EINVAL;

	return io_buffer_unregister_bvec(cmd, index, issue_flags);
}

static int ublk_check_fetch_buf(const struct ublk_device *ub, __u64 buf_addr)
{
	if (ublk_dev_need_map_io(ub)) {
		/*
		 * FETCH_RQ has to provide IO buffer if NEED GET
		 * DATA is not enabled
		 */
		if (!buf_addr && !ublk_dev_need_get_data(ub))
			return -EINVAL;
	} else if (buf_addr) {
		/* User copy requires addr to be unset */
		return -EINVAL;
	}
	return 0;
}

static int __ublk_fetch(struct io_uring_cmd *cmd, struct ublk_device *ub,
			struct ublk_io *io, u16 q_id)
{
	/* UBLK_IO_FETCH_REQ is only allowed before dev is setup */
	if (ublk_dev_ready(ub))
		return -EBUSY;

	/* allow each command to be FETCHed at most once */
	if (io->flags & UBLK_IO_FLAG_ACTIVE)
		return -EINVAL;

	WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV);

	ublk_fill_io_cmd(io, cmd);

	if (ublk_dev_support_batch_io(ub))
		WRITE_ONCE(io->task, NULL);
	else
		WRITE_ONCE(io->task, get_task_struct(current));

	return 0;
}

static int ublk_fetch(struct io_uring_cmd *cmd, struct ublk_device *ub,
		      struct ublk_io *io, __u64 buf_addr, u16 q_id)
{
	int ret;

	/*
	 * When handling FETCH command for setting up ublk uring queue,
	 * ub->mutex is the innermost lock, and we won't block for handling
	 * FETCH, so it is fine even for IO_URING_F_NONBLOCK.
	 */
	mutex_lock(&ub->mutex);
	ret = __ublk_fetch(cmd, ub, io, q_id);
	if (!ret)
		ret = ublk_config_io_buf(ub, io, cmd, buf_addr, NULL);
	if (!ret)
		ublk_mark_io_ready(ub, q_id, io);
	mutex_unlock(&ub->mutex);
	return ret;
}

static int ublk_check_commit_and_fetch(const struct ublk_device *ub,
				       struct ublk_io *io, __u64 buf_addr)
{
	struct request *req = io->req;

	if (ublk_dev_need_map_io(ub)) {
		/*
		 * COMMIT_AND_FETCH_REQ has to provide IO buffer if
		 * NEED GET DATA is not enabled or it is Read IO.
		 */
		if (!buf_addr && (!ublk_dev_need_get_data(ub) ||
					req_op(req) == REQ_OP_READ))
			return -EINVAL;
	} else if (req_op(req) != REQ_OP_ZONE_APPEND && buf_addr) {
		/*
		 * User copy requires addr to be unset when command is
		 * not zone append
		 */
		return -EINVAL;
	}

	return 0;
}

static bool ublk_need_complete_req(const struct ublk_device *ub,
				   struct ublk_io *io)
{
	if (ublk_dev_need_req_ref(ub))
		return ublk_sub_req_ref(io);
	return true;
}

static bool ublk_get_data(const struct ublk_queue *ubq, struct ublk_io *io,
			  struct request *req)
{
	/*
	 * 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->buf.addr;
	pr_devel("%s: update iod->addr: qid %d tag %d io_flags %x addr %llx\n",
			__func__, ubq->q_id, req->tag, io->flags,
			ublk_get_iod(ubq, req->tag)->addr);

	return ublk_start_io(ubq, req, io);
}

static int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd,
		unsigned int issue_flags)
{
	/* May point to userspace-mapped memory */
	const struct ublksrv_io_cmd *ub_src = io_uring_sqe_cmd(cmd->sqe,
							       struct ublksrv_io_cmd);
	u16 buf_idx = UBLK_INVALID_BUF_IDX;
	struct ublk_device *ub = cmd->file->private_data;
	struct ublk_queue *ubq;
	struct ublk_io *io = NULL;
	u32 cmd_op = cmd->cmd_op;
	u16 q_id = READ_ONCE(ub_src->q_id);
	u16 tag = READ_ONCE(ub_src->tag);
	s32 result = READ_ONCE(ub_src->result);
	u64 addr = READ_ONCE(ub_src->addr); /* unioned with zone_append_lba */
	struct request *req;
	int ret;
	bool compl;

	WARN_ON_ONCE(issue_flags & IO_URING_F_UNLOCKED);

	pr_devel("%s: received: cmd op %d queue %d tag %d result %d\n",
			__func__, cmd->cmd_op, q_id, tag, result);

	ret = ublk_check_cmd_op(cmd_op);
	if (ret)
		goto out;

	/*
	 * io_buffer_unregister_bvec() doesn't access the ubq or io,
	 * so no need to validate the q_id, tag, or task
	 */
	if (_IOC_NR(cmd_op) == UBLK_IO_UNREGISTER_IO_BUF)
		return ublk_unregister_io_buf(cmd, ub, addr, issue_flags);

	ret = -EINVAL;
	if (q_id >= ub->dev_info.nr_hw_queues)
		goto out;

	ubq = ublk_get_queue(ub, q_id);

	if (tag >= ub->dev_info.queue_depth)
		goto out;

	io = &ubq->ios[tag];
	/* UBLK_IO_FETCH_REQ can be handled on any task, which sets io->task */
	if (unlikely(_IOC_NR(cmd_op) == UBLK_IO_FETCH_REQ)) {
		ret = ublk_check_fetch_buf(ub, addr);
		if (ret)
			goto out;
		ret = ublk_fetch(cmd, ub, io, addr, q_id);
		if (ret)
			goto out;

		ublk_prep_cancel(cmd, issue_flags, ubq, tag);
		return -EIOCBQUEUED;
	}

	if (READ_ONCE(io->task) != current) {
		/*
		 * ublk_register_io_buf() accesses only the io's refcount,
		 * so can be handled on any task
		 */
		if (_IOC_NR(cmd_op) == UBLK_IO_REGISTER_IO_BUF)
			return ublk_register_io_buf(cmd, ub, q_id, tag, io,
						    addr, issue_flags);

		goto out;
	}

	/* there is pending io cmd, something must be wrong */
	if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV)) {
		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;

	switch (_IOC_NR(cmd_op)) {
	case UBLK_IO_REGISTER_IO_BUF:
		return ublk_daemon_register_io_buf(cmd, ub, q_id, tag, io, addr,
						   issue_flags);
	case UBLK_IO_COMMIT_AND_FETCH_REQ:
		ret = ublk_check_commit_and_fetch(ub, io, addr);
		if (ret)
			goto out;
		io->res = result;
		req = ublk_fill_io_cmd(io, cmd);
		ret = ublk_config_io_buf(ub, io, cmd, addr, &buf_idx);
		if (buf_idx != UBLK_INVALID_BUF_IDX)
			io_buffer_unregister_bvec(cmd, buf_idx, issue_flags);
		compl = ublk_need_complete_req(ub, io);

		if (req_op(req) == REQ_OP_ZONE_APPEND)
			req->__sector = addr;
		if (compl)
			__ublk_complete_rq(req, io, ublk_dev_need_map_io(ub), NULL);

		if (ret)
			goto out;
		break;
	case UBLK_IO_NEED_GET_DATA:
		/*
		 * ublk_get_data() may fail and fallback to requeue, so keep
		 * uring_cmd active first and prepare for handling new requeued
		 * request
		 */
		req = ublk_fill_io_cmd(io, cmd);
		ret = ublk_config_io_buf(ub, io, cmd, addr, NULL);
		WARN_ON_ONCE(ret);
		if (likely(ublk_get_data(ubq, io, req))) {
			__ublk_prep_compl_io_cmd(io, req);
			return UBLK_IO_RES_OK;
		}
		break;
	default:
		goto out;
	}
	ublk_prep_cancel(cmd, issue_flags, ubq, tag);
	return -EIOCBQUEUED;

 out:
	pr_devel("%s: complete: cmd op %d, tag %d ret %x io_flags %x\n",
			__func__, cmd_op, tag, ret, io ? io->flags : 0);
	return ret;
}

static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
		u16 q_id, u16 tag, struct ublk_io *io)
{
	struct request *req;

	/*
	 * can't use io->req in case of concurrent UBLK_IO_COMMIT_AND_FETCH_REQ,
	 * which would overwrite it with io->cmd
	 */
	req = blk_mq_tag_to_rq(ub->tag_set.tags[q_id], tag);
	if (!req)
		return NULL;

	if (!ublk_get_req_ref(io))
		return NULL;

	if (unlikely(!blk_mq_request_started(req) || req->tag != tag))
		goto fail_put;

	if (!ublk_rq_has_data(req))
		goto fail_put;

	return req;
fail_put:
	ublk_put_req_ref(io, req);
	return NULL;
}

static void ublk_ch_uring_cmd_cb(struct io_tw_req tw_req, io_tw_token_t tw)
{
	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
	int ret = ublk_ch_uring_cmd_local(cmd, issue_flags);

	if (ret != -EIOCBQUEUED)
		io_uring_cmd_done(cmd, ret, issue_flags);
}

static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
{
	if (unlikely(issue_flags & IO_URING_F_CANCEL)) {
		ublk_uring_cmd_cancel_fn(cmd, issue_flags);
		return 0;
	}

	/* well-implemented server won't run into unlocked */
	if (unlikely(issue_flags & IO_URING_F_UNLOCKED)) {
		io_uring_cmd_complete_in_task(cmd, ublk_ch_uring_cmd_cb);
		return -EIOCBQUEUED;
	}

	return ublk_ch_uring_cmd_local(cmd, issue_flags);
}

static inline __u64 ublk_batch_buf_addr(const struct ublk_batch_io *uc,
					const struct ublk_elem_header *elem)
{
	const void *buf = elem;

	if (uc->flags & UBLK_BATCH_F_HAS_BUF_ADDR)
		return *(const __u64 *)(buf + sizeof(*elem));
	return 0;
}

static inline __u64 ublk_batch_zone_lba(const struct ublk_batch_io *uc,
					const struct ublk_elem_header *elem)
{
	const void *buf = elem;

	if (uc->flags & UBLK_BATCH_F_HAS_ZONE_LBA)
		return *(const __u64 *)(buf + sizeof(*elem) +
				8 * !!(uc->flags & UBLK_BATCH_F_HAS_BUF_ADDR));
	return -1;
}

static struct ublk_auto_buf_reg
ublk_batch_auto_buf_reg(const struct ublk_batch_io *uc,
			const struct ublk_elem_header *elem)
{
	struct ublk_auto_buf_reg reg = {
		.index = elem->buf_index,
		.flags = (uc->flags & UBLK_BATCH_F_AUTO_BUF_REG_FALLBACK) ?
			UBLK_AUTO_BUF_REG_FALLBACK : 0,
	};

	return reg;
}

/*
 * 48 can hold any type of buffer element(8, 16 and 24 bytes) because
 * it is the least common multiple(LCM) of 8, 16 and 24
 */
#define UBLK_CMD_BATCH_TMP_BUF_SZ  (48 * 10)
struct ublk_batch_io_iter {
	void __user *uaddr;
	unsigned done, total;
	unsigned char elem_bytes;
	/* copy to this buffer from user space */
	unsigned char buf[UBLK_CMD_BATCH_TMP_BUF_SZ];
};

static inline int
__ublk_walk_cmd_buf(struct ublk_queue *ubq,
		    struct ublk_batch_io_iter *iter,
		    const struct ublk_batch_io_data *data,
		    unsigned bytes,
		    int (*cb)(struct ublk_queue *q,
			    const struct ublk_batch_io_data *data,
			    const struct ublk_elem_header *elem))
{
	unsigned int i;
	int ret = 0;

	for (i = 0; i < bytes; i += iter->elem_bytes) {
		const struct ublk_elem_header *elem =
			(const struct ublk_elem_header *)&iter->buf[i];

		if (unlikely(elem->tag >= data->ub->dev_info.queue_depth)) {
			ret = -EINVAL;
			break;
		}

		ret = cb(ubq, data, elem);
		if (unlikely(ret))
			break;
	}

	iter->done += i;
	return ret;
}

static int ublk_walk_cmd_buf(struct ublk_batch_io_iter *iter,
			     const struct ublk_batch_io_data *data,
			     int (*cb)(struct ublk_queue *q,
				     const struct ublk_batch_io_data *data,
				     const struct ublk_elem_header *elem))
{
	struct ublk_queue *ubq = ublk_get_queue(data->ub, data->header.q_id);
	int ret = 0;

	while (iter->done < iter->total) {
		unsigned int len = min(sizeof(iter->buf), iter->total - iter->done);

		if (copy_from_user(iter->buf, iter->uaddr + iter->done, len)) {
			pr_warn("ublk%d: read batch cmd buffer failed\n",
					data->ub->dev_info.dev_id);
			return -EFAULT;
		}

		ret = __ublk_walk_cmd_buf(ubq, iter, data, len, cb);
		if (ret)
			return ret;
	}
	return 0;
}

static int ublk_batch_unprep_io(struct ublk_queue *ubq,
				const struct ublk_batch_io_data *data,
				const struct ublk_elem_header *elem)
{
	struct ublk_io *io = &ubq->ios[elem->tag];

	/*
	 * If queue was ready before this decrement, it won't be anymore,
	 * so we need to decrement the queue ready count and restore the
	 * canceling flag to prevent new requests from being queued.
	 */
	if (ublk_queue_ready(ubq)) {
		data->ub->nr_queue_ready--;
		spin_lock(&ubq->cancel_lock);
		ubq->canceling = true;
		spin_unlock(&ubq->cancel_lock);
	}
	ubq->nr_io_ready--;

	ublk_io_lock(io);
	io->flags = 0;
	ublk_io_unlock(io);
	return 0;
}

static void ublk_batch_revert_prep_cmd(struct ublk_batch_io_iter *iter,
				       const struct ublk_batch_io_data *data)
{
	int ret;

	/* Re-process only what we've already processed, starting from beginning */
	iter->total = iter->done;
	iter->done = 0;

	ret = ublk_walk_cmd_buf(iter, data, ublk_batch_unprep_io);
	WARN_ON_ONCE(ret);
}

static int ublk_batch_prep_io(struct ublk_queue *ubq,
			      const struct ublk_batch_io_data *data,
			      const struct ublk_elem_header *elem)
{
	struct ublk_io *io = &ubq->ios[elem->tag];
	const struct ublk_batch_io *uc = &data->header;
	union ublk_io_buf buf = { 0 };
	int ret;

	if (ublk_dev_support_auto_buf_reg(data->ub))
		buf.auto_reg = ublk_batch_auto_buf_reg(uc, elem);
	else if (ublk_dev_need_map_io(data->ub)) {
		buf.addr = ublk_batch_buf_addr(uc, elem);

		ret = ublk_check_fetch_buf(data->ub, buf.addr);
		if (ret)
			return ret;
	}

	ublk_io_lock(io);
	ret = __ublk_fetch(data->cmd, data->ub, io, ubq->q_id);
	if (!ret)
		io->buf = buf;
	ublk_io_unlock(io);

	if (!ret)
		ublk_mark_io_ready(data->ub, ubq->q_id, io);

	return ret;
}

static int ublk_handle_batch_prep_cmd(const struct ublk_batch_io_data *data)
{
	const struct ublk_batch_io *uc = &data->header;
	struct io_uring_cmd *cmd = data->cmd;
	struct ublk_batch_io_iter iter = {
		.uaddr = u64_to_user_ptr(READ_ONCE(cmd->sqe->addr)),
		.total = uc->nr_elem * uc->elem_bytes,
		.elem_bytes = uc->elem_bytes,
	};
	int ret;

	mutex_lock(&data->ub->mutex);
	ret = ublk_walk_cmd_buf(&iter, data, ublk_batch_prep_io);

	if (ret && iter.done)
		ublk_batch_revert_prep_cmd(&iter, data);
	mutex_unlock(&data->ub->mutex);
	return ret;
}

static int ublk_batch_commit_io_check(const struct ublk_queue *ubq,
				      struct ublk_io *io,
				      union ublk_io_buf *buf)
{
	if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
		return -EBUSY;

	/* BATCH_IO doesn't support UBLK_F_NEED_GET_DATA */
	if (ublk_need_map_io(ubq) && !buf->addr)
		return -EINVAL;
	return 0;
}

static int ublk_batch_commit_io(struct ublk_queue *ubq,
				const struct ublk_batch_io_data *data,
				const struct ublk_elem_header *elem)
{
	struct ublk_io *io = &ubq->ios[elem->tag];
	const struct ublk_batch_io *uc = &data->header;
	u16 buf_idx = UBLK_INVALID_BUF_IDX;
	union ublk_io_buf buf = { 0 };
	struct request *req = NULL;
	bool auto_reg = false;
	bool compl = false;
	int ret;

	if (ublk_dev_support_auto_buf_reg(data->ub)) {
		buf.auto_reg = ublk_batch_auto_buf_reg(uc, elem);
		auto_reg = true;
	} else if (ublk_dev_need_map_io(data->ub))
		buf.addr = ublk_batch_buf_addr(uc, elem);

	ublk_io_lock(io);
	ret = ublk_batch_commit_io_check(ubq, io, &buf);
	if (!ret) {
		io->res = elem->result;
		io->buf = buf;
		req = ublk_fill_io_cmd(io, data->cmd);

		if (auto_reg)
			ublk_clear_auto_buf_reg(io, data->cmd, &buf_idx);
		compl = ublk_need_complete_req(data->ub, io);
	}
	ublk_io_unlock(io);

	if (unlikely(ret)) {
		pr_warn_ratelimited("%s: dev %u queue %u io %u: commit failure %d\n",
			__func__, data->ub->dev_info.dev_id, ubq->q_id,
			elem->tag, ret);
		return ret;
	}

	if (buf_idx != UBLK_INVALID_BUF_IDX)
		io_buffer_unregister_bvec(data->cmd, buf_idx, data->issue_flags);
	if (req_op(req) == REQ_OP_ZONE_APPEND)
		req->__sector = ublk_batch_zone_lba(uc, elem);
	if (compl)
		__ublk_complete_rq(req, io, ublk_dev_need_map_io(data->ub), data->iob);
	return 0;
}

static int ublk_handle_batch_commit_cmd(struct ublk_batch_io_data *data)
{
	const struct ublk_batch_io *uc = &data->header;
	struct io_uring_cmd *cmd = data->cmd;
	struct ublk_batch_io_iter iter = {
		.uaddr = u64_to_user_ptr(READ_ONCE(cmd->sqe->addr)),
		.total = uc->nr_elem * uc->elem_bytes,
		.elem_bytes = uc->elem_bytes,
	};
	DEFINE_IO_COMP_BATCH(iob);
	int ret;

	data->iob = &iob;
	ret = ublk_walk_cmd_buf(&iter, data, ublk_batch_commit_io);

	if (iob.complete)
		iob.complete(&iob);

	return iter.done == 0 ? ret : iter.done;
}

static int ublk_check_batch_cmd_flags(const struct ublk_batch_io *uc)
{
	unsigned elem_bytes = sizeof(struct ublk_elem_header);

	if (uc->flags & ~UBLK_BATCH_F_ALL)
		return -EINVAL;

	/* UBLK_BATCH_F_AUTO_BUF_REG_FALLBACK requires buffer index */
	if ((uc->flags & UBLK_BATCH_F_AUTO_BUF_REG_FALLBACK) &&
			(uc->flags & UBLK_BATCH_F_HAS_BUF_ADDR))
		return -EINVAL;

	elem_bytes += (uc->flags & UBLK_BATCH_F_HAS_ZONE_LBA ? sizeof(u64) : 0) +
		(uc->flags & UBLK_BATCH_F_HAS_BUF_ADDR ? sizeof(u64) : 0);
	if (uc->elem_bytes != elem_bytes)
		return -EINVAL;
	return 0;
}

static int ublk_check_batch_cmd(const struct ublk_batch_io_data *data)
{
	const struct ublk_batch_io *uc = &data->header;

	if (uc->q_id >= data->ub->dev_info.nr_hw_queues)
		return -EINVAL;

	if (uc->nr_elem > data->ub->dev_info.queue_depth)
		return -E2BIG;

	if ((uc->flags & UBLK_BATCH_F_HAS_ZONE_LBA) &&
			!ublk_dev_is_zoned(data->ub))
		return -EINVAL;

	if ((uc->flags & UBLK_BATCH_F_HAS_BUF_ADDR) &&
			!ublk_dev_need_map_io(data->ub))
		return -EINVAL;

	if ((uc->flags & UBLK_BATCH_F_AUTO_BUF_REG_FALLBACK) &&
			!ublk_dev_support_auto_buf_reg(data->ub))
		return -EINVAL;

	return ublk_check_batch_cmd_flags(uc);
}

static int ublk_batch_attach(struct ublk_queue *ubq,
			     struct ublk_batch_io_data *data,
			     struct ublk_batch_fetch_cmd *fcmd)
{
	struct ublk_batch_fetch_cmd *new_fcmd = NULL;
	bool free = false;
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(data->cmd);

	spin_lock(&ubq->evts_lock);
	if (unlikely(ubq->force_abort || ubq->canceling)) {
		free = true;
	} else {
		list_add_tail(&fcmd->node, &ubq->fcmd_head);
		new_fcmd = __ublk_acquire_fcmd(ubq);
	}
	spin_unlock(&ubq->evts_lock);

	if (unlikely(free)) {
		ublk_batch_free_fcmd(fcmd);
		return -ENODEV;
	}

	pdu->ubq = ubq;
	pdu->fcmd = fcmd;
	io_uring_cmd_mark_cancelable(fcmd->cmd, data->issue_flags);

	if (!new_fcmd)
		goto out;

	/*
	 * If the two fetch commands are originated from same io_ring_ctx,
	 * run batch dispatch directly. Otherwise, schedule task work for
	 * doing it.
	 */
	if (io_uring_cmd_ctx_handle(new_fcmd->cmd) ==
			io_uring_cmd_ctx_handle(fcmd->cmd)) {
		data->cmd = new_fcmd->cmd;
		ublk_batch_dispatch(ubq, data, new_fcmd);
	} else {
		io_uring_cmd_complete_in_task(new_fcmd->cmd,
				ublk_batch_tw_cb);
	}
out:
	return -EIOCBQUEUED;
}

static int ublk_handle_batch_fetch_cmd(struct ublk_batch_io_data *data)
{
	struct ublk_queue *ubq = ublk_get_queue(data->ub, data->header.q_id);
	struct ublk_batch_fetch_cmd *fcmd = ublk_batch_alloc_fcmd(data->cmd);

	if (!fcmd)
		return -ENOMEM;

	return ublk_batch_attach(ubq, data, fcmd);
}

static int ublk_validate_batch_fetch_cmd(struct ublk_batch_io_data *data)
{
	const struct ublk_batch_io *uc = &data->header;

	if (uc->q_id >= data->ub->dev_info.nr_hw_queues)
		return -EINVAL;

	if (!(data->cmd->flags & IORING_URING_CMD_MULTISHOT))
		return -EINVAL;

	if (uc->elem_bytes != sizeof(__u16))
		return -EINVAL;

	if (uc->flags != 0)
		return -EINVAL;

	return 0;
}

static int ublk_handle_non_batch_cmd(struct io_uring_cmd *cmd,
				     unsigned int issue_flags)
{
	const struct ublksrv_io_cmd *ub_cmd = io_uring_sqe_cmd(cmd->sqe,
							       struct ublksrv_io_cmd);
	struct ublk_device *ub = cmd->file->private_data;
	unsigned tag = READ_ONCE(ub_cmd->tag);
	unsigned q_id = READ_ONCE(ub_cmd->q_id);
	unsigned index = READ_ONCE(ub_cmd->addr);
	struct ublk_queue *ubq;
	struct ublk_io *io;

	if (cmd->cmd_op == UBLK_U_IO_UNREGISTER_IO_BUF)
		return ublk_unregister_io_buf(cmd, ub, index, issue_flags);

	if (q_id >= ub->dev_info.nr_hw_queues)
		return -EINVAL;

	if (tag >= ub->dev_info.queue_depth)
		return -EINVAL;

	if (cmd->cmd_op != UBLK_U_IO_REGISTER_IO_BUF)
		return -EOPNOTSUPP;

	ubq = ublk_get_queue(ub, q_id);
	io = &ubq->ios[tag];
	return ublk_register_io_buf(cmd, ub, q_id, tag, io, index,
			issue_flags);
}

static int ublk_ch_batch_io_uring_cmd(struct io_uring_cmd *cmd,
				       unsigned int issue_flags)
{
	const struct ublk_batch_io *uc = io_uring_sqe_cmd(cmd->sqe,
							  struct ublk_batch_io);
	struct ublk_device *ub = cmd->file->private_data;
	struct ublk_batch_io_data data = {
		.ub  = ub,
		.cmd = cmd,
		.header = (struct ublk_batch_io) {
			.q_id = READ_ONCE(uc->q_id),
			.flags = READ_ONCE(uc->flags),
			.nr_elem = READ_ONCE(uc->nr_elem),
			.elem_bytes = READ_ONCE(uc->elem_bytes),
		},
		.issue_flags = issue_flags,
	};
	u32 cmd_op = cmd->cmd_op;
	int ret = -EINVAL;

	if (unlikely(issue_flags & IO_URING_F_CANCEL)) {
		ublk_batch_cancel_fn(cmd, issue_flags);
		return 0;
	}

	switch (cmd_op) {
	case UBLK_U_IO_PREP_IO_CMDS:
		ret = ublk_check_batch_cmd(&data);
		if (ret)
			goto out;
		ret = ublk_handle_batch_prep_cmd(&data);
		break;
	case UBLK_U_IO_COMMIT_IO_CMDS:
		ret = ublk_check_batch_cmd(&data);
		if (ret)
			goto out;
		ret = ublk_handle_batch_commit_cmd(&data);
		break;
	case UBLK_U_IO_FETCH_IO_CMDS:
		ret = ublk_validate_batch_fetch_cmd(&data);
		if (ret)
			goto out;
		ret = ublk_handle_batch_fetch_cmd(&data);
		break;
	default:
		ret = ublk_handle_non_batch_cmd(cmd, issue_flags);
		break;
	}
out:
	return ret;
}

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 ssize_t
ublk_user_copy(struct kiocb *iocb, struct iov_iter *iter, int dir)
{
	struct ublk_device *ub = iocb->ki_filp->private_data;
	struct ublk_queue *ubq;
	struct request *req;
	struct ublk_io *io;
	unsigned data_len;
	bool is_integrity;
	bool on_daemon;
	size_t buf_off;
	u16 tag, q_id;
	ssize_t ret;

	if (!user_backed_iter(iter))
		return -EACCES;

	if (ub->dev_info.state == UBLK_S_DEV_DEAD)
		return -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);
	is_integrity = !!(iocb->ki_pos & UBLKSRV_IO_INTEGRITY_FLAG);

	if (unlikely(!ublk_dev_support_integrity(ub) && is_integrity))
		return -EINVAL;

	if (q_id >= ub->dev_info.nr_hw_queues)
		return -EINVAL;

	ubq = ublk_get_queue(ub, q_id);
	if (!ublk_dev_support_user_copy(ub))
		return -EACCES;

	if (tag >= ub->dev_info.queue_depth)
		return -EINVAL;

	io = &ubq->ios[tag];
	on_daemon = current == READ_ONCE(io->task);
	if (on_daemon) {
		/* On daemon, io can't be completed concurrently, so skip ref */
		if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
			return -EINVAL;

		req = io->req;
		if (!ublk_rq_has_data(req))
			return -EINVAL;
	} else {
		req = __ublk_check_and_get_req(ub, q_id, tag, io);
		if (!req)
			return -EINVAL;
	}

	if (is_integrity) {
		struct blk_integrity *bi = &req->q->limits.integrity;

		data_len = bio_integrity_bytes(bi, blk_rq_sectors(req));
	} else {
		data_len = blk_rq_bytes(req);
	}
	if (buf_off > data_len) {
		ret = -EINVAL;
		goto out;
	}

	if (!ublk_check_ubuf_dir(req, dir)) {
		ret = -EACCES;
		goto out;
	}

	if (is_integrity)
		ret = ublk_copy_user_integrity(req, buf_off, iter, dir);
	else
		ret = ublk_copy_user_pages(req, buf_off, iter, dir);

out:
	if (!on_daemon)
		ublk_put_req_ref(io, req);
	return ret;
}

static ssize_t ublk_ch_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
	return ublk_user_copy(iocb, to, ITER_DEST);
}

static ssize_t ublk_ch_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
	return ublk_user_copy(iocb, from, ITER_SOURCE);
}

static const struct file_operations ublk_ch_fops = {
	.owner = THIS_MODULE,
	.open = ublk_ch_open,
	.release = ublk_ch_release,
	.read_iter = ublk_ch_read_iter,
	.write_iter = ublk_ch_write_iter,
	.uring_cmd = ublk_ch_uring_cmd,
	.mmap = ublk_ch_mmap,
};

static const struct file_operations ublk_ch_batch_io_fops = {
	.owner = THIS_MODULE,
	.open = ublk_ch_open,
	.release = ublk_ch_release,
	.read_iter = ublk_ch_read_iter,
	.write_iter = ublk_ch_write_iter,
	.uring_cmd = ublk_ch_batch_io_uring_cmd,
	.mmap = ublk_ch_mmap,
};

static void __ublk_deinit_queue(struct ublk_device *ub, struct ublk_queue *ubq)
{
	int size, i;

	size = ublk_queue_cmd_buf_size(ub);

	for (i = 0; i < ubq->q_depth; i++) {
		struct ublk_io *io = &ubq->ios[i];
		if (io->task)
			put_task_struct(io->task);
		WARN_ON_ONCE(refcount_read(&io->ref));
		WARN_ON_ONCE(io->task_registered_buffers);
	}

	if (ubq->io_cmd_buf)
		free_pages((unsigned long)ubq->io_cmd_buf, get_order(size));

	if (ublk_dev_support_batch_io(ub))
		ublk_io_evts_deinit(ubq);

	kvfree(ubq);
}

static void ublk_deinit_queue(struct ublk_device *ub, int q_id)
{
	struct ublk_queue *ubq = ub->queues[q_id];

	if (!ubq)
		return;

	__ublk_deinit_queue(ub, ubq);
	ub->queues[q_id] = NULL;
}

static int ublk_get_queue_numa_node(struct ublk_device *ub, int q_id)
{
	unsigned int cpu;

	/* Find first CPU mapped to this queue */
	for_each_possible_cpu(cpu) {
		if (ub->tag_set.map[HCTX_TYPE_DEFAULT].mq_map[cpu] == q_id)
			return cpu_to_node(cpu);
	}

	return NUMA_NO_NODE;
}

static int ublk_init_queue(struct ublk_device *ub, int q_id)
{
	int depth = ub->dev_info.queue_depth;
	gfp_t gfp_flags = GFP_KERNEL | __GFP_ZERO;
	struct ublk_queue *ubq;
	struct page *page;
	int numa_node;
	int size, i, ret;

	/* Determine NUMA node based on queue's CPU affinity */
	numa_node = ublk_get_queue_numa_node(ub, q_id);

	/* Allocate queue structure on local NUMA node */
	ubq = kvzalloc_node(struct_size(ubq, ios, depth), GFP_KERNEL,
			    numa_node);
	if (!ubq)
		return -ENOMEM;

	spin_lock_init(&ubq->cancel_lock);
	ubq->flags = ub->dev_info.flags;
	ubq->q_id = q_id;
	ubq->q_depth = depth;
	size = ublk_queue_cmd_buf_size(ub);

	/* Allocate I/O command buffer on local NUMA node */
	page = alloc_pages_node(numa_node, gfp_flags, get_order(size));
	if (!page) {
		kvfree(ubq);
		return -ENOMEM;
	}
	ubq->io_cmd_buf = page_address(page);

	for (i = 0; i < ubq->q_depth; i++)
		spin_lock_init(&ubq->ios[i].lock);

	if (ublk_dev_support_batch_io(ub)) {
		ret = ublk_io_evts_init(ubq, ubq->q_depth, numa_node);
		if (ret)
			goto fail;
		INIT_LIST_HEAD(&ubq->fcmd_head);
	}
	ub->queues[q_id] = ubq;
	ubq->dev = ub;

	return 0;
fail:
	__ublk_deinit_queue(ub, ubq);
	return ret;
}

static void ublk_deinit_queues(struct ublk_device *ub)
{
	int i;

	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
		ublk_deinit_queue(ub, i);
}

static int ublk_init_queues(struct ublk_device *ub)
{
	int i, ret;

	for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
		ret = ublk_init_queue(ub, i);
		if (ret)
			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, UBLK_MAX_UBLKS,
				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);

	ublk_buf_cleanup(ub);
	blk_mq_free_tag_set(&ub->tag_set);
	ublk_deinit_queues(ub);
	ublk_free_dev_number(ub);
	mutex_destroy(&ub->mutex);
	mutex_destroy(&ub->cancel_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;

	if (ublk_dev_support_batch_io(ub))
		cdev_init(&ub->cdev, &ublk_ch_batch_io_fops);
	else
		cdev_init(&ub->cdev, &ublk_ch_fops);
	ret = cdev_device_add(&ub->cdev, dev);
	if (ret)
		goto fail;

	if (ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV)
		unprivileged_ublks_added++;
	return 0;
 fail:
	put_device(dev);
	return ret;
}

/* 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)
{
	if (ublk_dev_support_batch_io(ub))
		ub->tag_set.ops = &ublk_batch_mq_ops;
	else
		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.driver_data = ub;
	return blk_mq_alloc_tag_set(&ub->tag_set);
}

static void ublk_remove(struct ublk_device *ub)
{
	bool unprivileged;

	ublk_stop_dev(ub);
	cdev_device_del(&ub->cdev, &ub->cdev_dev);
	unprivileged = ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV;
	ublk_put_device(ub);

	if (unprivileged)
		unprivileged_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 bool ublk_validate_user_pid(struct ublk_device *ub, pid_t ublksrv_pid)
{
	rcu_read_lock();
	ublksrv_pid = pid_nr(find_vpid(ublksrv_pid));
	rcu_read_unlock();

	return ub->ublksrv_tgid == ublksrv_pid;
}

static int ublk_ctrl_start_dev(struct ublk_device *ub,
		const struct ublksrv_ctrl_cmd *header)
{
	const struct ublk_param_basic *p = &ub->params.basic;
	int ublksrv_pid = (int)header->data[0];
	struct queue_limits lim = {
		.logical_block_size	= 1 << p->logical_bs_shift,
		.physical_block_size	= 1 << p->physical_bs_shift,
		.io_min			= 1 << p->io_min_shift,
		.io_opt			= 1 << p->io_opt_shift,
		.max_hw_sectors		= p->max_sectors,
		.chunk_sectors		= p->chunk_sectors,
		.virt_boundary_mask	= p->virt_boundary_mask,
		.max_segments		= USHRT_MAX,
		.max_segment_size	= UINT_MAX,
		.dma_alignment		= 3,
	};
	struct gendisk *disk;
	int ret = -EINVAL;

	if (ublksrv_pid <= 0)
		return -EINVAL;
	if (!(ub->params.types & UBLK_PARAM_TYPE_BASIC))
		return -EINVAL;

	if (ub->params.types & UBLK_PARAM_TYPE_DISCARD) {
		const struct ublk_param_discard *pd = &ub->params.discard;

		lim.discard_alignment = pd->discard_alignment;
		lim.discard_granularity = pd->discard_granularity;
		lim.max_hw_discard_sectors = pd->max_discard_sectors;
		lim.max_write_zeroes_sectors = pd->max_write_zeroes_sectors;
		lim.max_discard_segments = pd->max_discard_segments;
	}

	if (ub->params.types & UBLK_PARAM_TYPE_ZONED) {
		const struct ublk_param_zoned *p = &ub->params.zoned;

		if (!IS_ENABLED(CONFIG_BLK_DEV_ZONED))
			return -EOPNOTSUPP;

		lim.features |= BLK_FEAT_ZONED;
		lim.max_active_zones = p->max_active_zones;
		lim.max_open_zones =  p->max_open_zones;
		lim.max_hw_zone_append_sectors = p->max_zone_append_sectors;
	}

	if (ub->params.basic.attrs & UBLK_ATTR_VOLATILE_CACHE) {
		lim.features |= BLK_FEAT_WRITE_CACHE;
		if (ub->params.basic.attrs & UBLK_ATTR_FUA)
			lim.features |= BLK_FEAT_FUA;
	}

	if (ub->params.basic.attrs & UBLK_ATTR_ROTATIONAL)
		lim.features |= BLK_FEAT_ROTATIONAL;

	if (ub->params.types & UBLK_PARAM_TYPE_DMA_ALIGN)
		lim.dma_alignment = ub->params.dma.alignment;

	if (ub->params.types & UBLK_PARAM_TYPE_SEGMENT) {
		lim.seg_boundary_mask = ub->params.seg.seg_boundary_mask;
		lim.max_segment_size = ub->params.seg.max_segment_size;
		lim.max_segments = ub->params.seg.max_segments;
	}

	if (ub->params.types & UBLK_PARAM_TYPE_INTEGRITY) {
		const struct ublk_param_integrity *p = &ub->params.integrity;
		int pi_tuple_size = ublk_integrity_pi_tuple_size(p->csum_type);

		lim.max_integrity_segments =
			p->max_integrity_segments ?: USHRT_MAX;
		lim.integrity = (struct blk_integrity) {
			.flags = ublk_integrity_flags(p->flags),
			.csum_type = ublk_integrity_csum_type(p->csum_type),
			.metadata_size = p->metadata_size,
			.pi_offset = p->pi_offset,
			.interval_exp = p->interval_exp,
			.tag_size = p->tag_size,
			.pi_tuple_size = pi_tuple_size,
		};
	}

	if (wait_for_completion_interruptible(&ub->completion) != 0)
		return -EINTR;

	if (!ublk_validate_user_pid(ub, ublksrv_pid))
		return -EINVAL;

	mutex_lock(&ub->mutex);
	/* device may become not ready in case of F_BATCH */
	if (!ublk_dev_ready(ub)) {
		ret = -EINVAL;
		goto out_unlock;
	}
	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, &lim, 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 = ub->ublksrv_tgid;
	ub->ub_disk = disk;

	ublk_apply_params(ub);

	/*
	 * Suppress partition scan to avoid potential IO hang.
	 *
	 * If ublk server error occurs during partition scan, the IO may
	 * wait while holding ub->mutex, which can deadlock with other
	 * operations that need the mutex. Defer partition scan to async
	 * work.
	 * For unprivileged daemons, keep GD_SUPPRESS_PART_SCAN set
	 * permanently.
	 */
	set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);

	ublk_get_device(ub);
	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);

	/* Skip partition scan if disabled by user */
	if (ub->dev_info.flags & UBLK_F_NO_AUTO_PART_SCAN) {
		/* Not clear for unprivileged daemons, see comment above */
		if (!ub->unprivileged_daemons)
			clear_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
	} else {
		/* Schedule async partition scan for trusted daemons */
		if (!ub->unprivileged_daemons)
			schedule_work(&ub->partition_scan_work);
	}

out_put_cdev:
	if (ret) {
		ublk_detach_disk(ub);
		ublk_put_device(ub);
	}
	if (ret)
		put_disk(disk);
out_unlock:
	mutex_unlock(&ub->mutex);
	return ret;
}

static int ublk_ctrl_get_queue_affinity(struct ublk_device *ub,
		const struct ublksrv_ctrl_cmd *header)
{
	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(const struct ublksrv_ctrl_cmd *header)
{
	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 (info.queue_depth > UBLK_MAX_QUEUE_DEPTH || !info.queue_depth ||
	    info.nr_hw_queues > UBLK_MAX_NR_QUEUES || !info.nr_hw_queues)
		return -EINVAL;

	if (capable(CAP_SYS_ADMIN))
		info.flags &= ~UBLK_F_UNPRIVILEGED_DEV;
	else if (!(info.flags & UBLK_F_UNPRIVILEGED_DEV))
		return -EPERM;

	/* forbid nonsense combinations of recovery flags */
	switch (info.flags & UBLK_F_ALL_RECOVERY_FLAGS) {
	case 0:
	case UBLK_F_USER_RECOVERY:
	case (UBLK_F_USER_RECOVERY | UBLK_F_USER_RECOVERY_REISSUE):
	case (UBLK_F_USER_RECOVERY | UBLK_F_USER_RECOVERY_FAIL_IO):
		break;
	default:
		pr_warn("%s: invalid recovery flags %llx\n", __func__,
			info.flags & UBLK_F_ALL_RECOVERY_FLAGS);
		return -EINVAL;
	}

	if ((info.flags & UBLK_F_QUIESCE) && !(info.flags & UBLK_F_USER_RECOVERY)) {
		pr_warn("UBLK_F_QUIESCE requires UBLK_F_USER_RECOVERY\n");
		return -EINVAL;
	}

	/*
	 * 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);

		/*
		 * For USER_COPY, we depends on userspace to fill request
		 * buffer by pwrite() to ublk char device, which can't be
		 * used for unprivileged device
		 *
		 * Same with zero copy or auto buffer register.
		 */
		if (info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY |
					UBLK_F_AUTO_BUF_REG))
			return -EINVAL;
	}

	/* User copy is required to access integrity buffer */
	if (info.flags & UBLK_F_INTEGRITY && !(info.flags & UBLK_F_USER_COPY))
		return -EINVAL;

	/* 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;
	}

	if (header->dev_id != U32_MAX && header->dev_id >= UBLK_MAX_UBLKS) {
		pr_warn("%s: dev id is too large. Max supported is %d\n",
			__func__, UBLK_MAX_UBLKS - 1);
		return -EINVAL;
	}

	ublk_dump_dev_info(&info);

	ret = mutex_lock_killable(&ublk_ctl_mutex);
	if (ret)
		return ret;

	ret = -EACCES;
	if ((info.flags & UBLK_F_UNPRIVILEGED_DEV) &&
	    unprivileged_ublks_added >= unprivileged_ublks_max)
		goto out_unlock;

	ret = -ENOMEM;
	ub = kzalloc_flex(*ub, queues, info.nr_hw_queues);
	if (!ub)
		goto out_unlock;
	mutex_init(&ub->mutex);
	spin_lock_init(&ub->lock);
	mutex_init(&ub->cancel_mutex);
	mt_init(&ub->buf_tree);
	ida_init(&ub->buf_ida);
	INIT_WORK(&ub->partition_scan_work, ublk_partition_scan_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 |
		UBLK_F_PER_IO_DAEMON |
		UBLK_F_BUF_REG_OFF_DAEMON |
		UBLK_F_SAFE_STOP_DEV;

	/* So far, UBLK_F_PER_IO_DAEMON won't be exposed for BATCH_IO */
	if (ublk_dev_support_batch_io(ub))
		ub->dev_info.flags &= ~UBLK_F_PER_IO_DAEMON;

	/* GET_DATA isn't needed any more with USER_COPY or ZERO COPY */
	if (ub->dev_info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY |
				UBLK_F_AUTO_BUF_REG))
		ub->dev_info.flags &= ~UBLK_F_NEED_GET_DATA;

	/* UBLK_F_BATCH_IO doesn't support GET_DATA */
	if (ublk_dev_support_batch_io(ub))
		ub->dev_info.flags &= ~UBLK_F_NEED_GET_DATA;

	/*
	 * Zoned storage support requires reuse `ublksrv_io_cmd->addr` for
	 * returning write_append_lba, which is only allowed in case of
	 * user copy or zero copy
	 */
	if (ublk_dev_is_zoned(ub) &&
	    (!IS_ENABLED(CONFIG_BLK_DEV_ZONED) || !(ub->dev_info.flags &
	     (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY)))) {
		ret = -EINVAL;
		goto out_free_dev_number;
	}

	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_add_tag_set(ub);
	if (ret)
		goto out_free_dev_number;

	ret = ublk_init_queues(ub);
	if (ret)
		goto out_free_tag_set;

	ret = -EFAULT;
	if (copy_to_user(argp, &ub->dev_info, sizeof(info)))
		goto out_deinit_queues;

	/*
	 * 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_deinit_queues:
	ublk_deinit_queues(ub);
out_free_tag_set:
	blk_mq_free_tag_set(&ub->tag_set);
out_free_dev_number:
	ublk_free_dev_number(ub);
out_free_ub:
	mutex_destroy(&ub->mutex);
	mutex_destroy(&ub->cancel_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, bool wait)
{
	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 && wait_event_interruptible(ublk_idr_wq, ublk_idr_freed(idx)))
		return -EINTR;
	return 0;
}

static inline void ublk_ctrl_cmd_dump(u32 cmd_op,
				      const struct ublksrv_ctrl_cmd *header)
{
	pr_devel("%s: cmd_op %x, dev id %d qid %d data %llx buf %llx len %u\n",
			__func__, cmd_op, header->dev_id, header->queue_id,
			header->data[0], header->addr, header->len);
}

static void ublk_ctrl_stop_dev(struct ublk_device *ub)
{
	ublk_stop_dev(ub);
}

static int ublk_ctrl_try_stop_dev(struct ublk_device *ub)
{
	struct gendisk *disk;
	int ret = 0;

	disk = ublk_get_disk(ub);
	if (!disk)
		return -ENODEV;

	mutex_lock(&disk->open_mutex);
	if (disk_openers(disk) > 0) {
		ret = -EBUSY;
		goto unlock;
	}
	ub->block_open = true;
	/* release open_mutex as del_gendisk() will reacquire it */
	mutex_unlock(&disk->open_mutex);

	ublk_ctrl_stop_dev(ub);
	goto out;

unlock:
	mutex_unlock(&disk->open_mutex);
out:
	ublk_put_disk(disk);
	return ret;
}

static int ublk_ctrl_get_dev_info(struct ublk_device *ub,
		const struct ublksrv_ctrl_cmd *header)
{
	struct task_struct *p;
	struct pid *pid;
	struct ublksrv_ctrl_dev_info dev_info;
	pid_t init_ublksrv_tgid = ub->dev_info.ublksrv_pid;
	void __user *argp = (void __user *)(unsigned long)header->addr;

	if (header->len < sizeof(struct ublksrv_ctrl_dev_info) || !header->addr)
		return -EINVAL;

	memcpy(&dev_info, &ub->dev_info, sizeof(dev_info));
	dev_info.ublksrv_pid = -1;

	if (init_ublksrv_tgid > 0) {
		rcu_read_lock();
		pid = find_pid_ns(init_ublksrv_tgid, &init_pid_ns);
		p = pid_task(pid, PIDTYPE_TGID);
		if (p) {
			int vnr = task_tgid_vnr(p);

			if (vnr)
				dev_info.ublksrv_pid = vnr;
		}
		rcu_read_unlock();
	}

	if (copy_to_user(argp, &dev_info, sizeof(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,
		const struct ublksrv_ctrl_cmd *header)
{
	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,
		const struct ublksrv_ctrl_cmd *header)
{
	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);

	mutex_lock(&ub->mutex);
	if (test_bit(UB_STATE_USED, &ub->state)) {
		/*
		 * Parameters can only be changed when device hasn't
		 * been started yet
		 */
		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 int ublk_ctrl_start_recovery(struct ublk_device *ub)
{
	int ret = -EINVAL;

	mutex_lock(&ub->mutex);
	if (ublk_nosrv_should_stop_dev(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.
	 *
	 * and one of the following holds
	 *
	 * (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
	 *
	 * (3) UBLK_S_DEV_FAIL_IO is set, which means the queue is not
	 *     quiesced, but all I/O is being immediately errored
	 */
	if (test_bit(UB_STATE_OPEN, &ub->state) || !ublk_dev_in_recoverable_state(ub)) {
		ret = -EBUSY;
		goto out_unlock;
	}
	pr_devel("%s: start recovery for dev id %d\n", __func__, ub->ub_number);
	init_completion(&ub->completion);
	ret = 0;
 out_unlock:
	mutex_unlock(&ub->mutex);
	return ret;
}

static int ublk_ctrl_end_recovery(struct ublk_device *ub,
		const struct ublksrv_ctrl_cmd *header)
{
	int ublksrv_pid = (int)header->data[0];
	int ret = -EINVAL;

	pr_devel("%s: Waiting for all FETCH_REQs, dev id %d...\n", __func__,
		 header->dev_id);

	if (wait_for_completion_interruptible(&ub->completion))
		return -EINTR;

	pr_devel("%s: All FETCH_REQs received, dev id %d\n", __func__,
		 header->dev_id);

	if (!ublk_validate_user_pid(ub, ublksrv_pid))
		return -EINVAL;

	mutex_lock(&ub->mutex);
	if (ublk_nosrv_should_stop_dev(ub))
		goto out_unlock;

	if (!ublk_dev_in_recoverable_state(ub)) {
		ret = -EBUSY;
		goto out_unlock;
	}
	ub->dev_info.ublksrv_pid = ub->ublksrv_tgid;
	ub->dev_info.state = UBLK_S_DEV_LIVE;
	pr_devel("%s: new ublksrv_pid %d, dev id %d\n",
			__func__, ublksrv_pid, header->dev_id);
	blk_mq_kick_requeue_list(ub->ub_disk->queue);
	ret = 0;
 out_unlock:
	mutex_unlock(&ub->mutex);
	return ret;
}

static int ublk_ctrl_get_features(const struct ublksrv_ctrl_cmd *header)
{
	void __user *argp = (void __user *)(unsigned long)header->addr;
	u64 features = UBLK_F_ALL;

	if (header->len != UBLK_FEATURES_LEN || !header->addr)
		return -EINVAL;

	if (copy_to_user(argp, &features, UBLK_FEATURES_LEN))
		return -EFAULT;

	return 0;
}

static int ublk_ctrl_set_size(struct ublk_device *ub, const struct ublksrv_ctrl_cmd *header)
{
	struct ublk_param_basic *p = &ub->params.basic;
	u64 new_size = header->data[0];
	int ret = 0;

	mutex_lock(&ub->mutex);
	if (!ub->ub_disk) {
		ret = -ENODEV;
		goto out;
	}
	p->dev_sectors = new_size;
	set_capacity_and_notify(ub->ub_disk, p->dev_sectors);
out:
	mutex_unlock(&ub->mutex);
	return ret;
}

struct count_busy {
	const struct ublk_queue *ubq;
	unsigned int nr_busy;
};

static bool ublk_count_busy_req(struct request *rq, void *data)
{
	struct count_busy *idle = data;

	if (!blk_mq_request_started(rq) && rq->mq_hctx->driver_data == idle->ubq)
		idle->nr_busy += 1;
	return true;
}

/* uring_cmd is guaranteed to be active if the associated request is idle */
static bool ubq_has_idle_io(const struct ublk_queue *ubq)
{
	struct count_busy data = {
		.ubq = ubq,
	};

	blk_mq_tagset_busy_iter(&ubq->dev->tag_set, ublk_count_busy_req, &data);
	return data.nr_busy < ubq->q_depth;
}

/* Wait until each hw queue has at least one idle IO */
static int ublk_wait_for_idle_io(struct ublk_device *ub,
				 unsigned int timeout_ms)
{
	unsigned int elapsed = 0;
	int ret;

	/*
	 * For UBLK_F_BATCH_IO ublk server can get notified with existing
	 * or new fetch command, so needn't wait any more
	 */
	if (ublk_dev_support_batch_io(ub))
		return 0;

	while (elapsed < timeout_ms && !signal_pending(current)) {
		unsigned int queues_cancelable = 0;
		int i;

		for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
			struct ublk_queue *ubq = ublk_get_queue(ub, i);

			queues_cancelable += !!ubq_has_idle_io(ubq);
		}

		/*
		 * Each queue needs at least one active command for
		 * notifying ublk server
		 */
		if (queues_cancelable == ub->dev_info.nr_hw_queues)
			break;

		msleep(UBLK_REQUEUE_DELAY_MS);
		elapsed += UBLK_REQUEUE_DELAY_MS;
	}

	if (signal_pending(current))
		ret = -EINTR;
	else if (elapsed >= timeout_ms)
		ret = -EBUSY;
	else
		ret = 0;

	return ret;
}

static int ublk_ctrl_quiesce_dev(struct ublk_device *ub,
				 const struct ublksrv_ctrl_cmd *header)
{
	/* zero means wait forever */
	u64 timeout_ms = header->data[0];
	struct gendisk *disk;
	int ret = -ENODEV;

	if (!(ub->dev_info.flags & UBLK_F_QUIESCE))
		return -EOPNOTSUPP;

	mutex_lock(&ub->mutex);
	disk = ublk_get_disk(ub);
	if (!disk)
		goto unlock;
	if (ub->dev_info.state == UBLK_S_DEV_DEAD)
		goto put_disk;

	ret = 0;
	/* already in expected state */
	if (ub->dev_info.state != UBLK_S_DEV_LIVE)
		goto put_disk;

	/* Mark the device as canceling */
	mutex_lock(&ub->cancel_mutex);
	blk_mq_quiesce_queue(disk->queue);
	ublk_set_canceling(ub, true);
	blk_mq_unquiesce_queue(disk->queue);
	mutex_unlock(&ub->cancel_mutex);

	if (!timeout_ms)
		timeout_ms = UINT_MAX;
	ret = ublk_wait_for_idle_io(ub, timeout_ms);

put_disk:
	ublk_put_disk(disk);
unlock:
	mutex_unlock(&ub->mutex);

	/* Cancel pending uring_cmd */
	if (!ret)
		ublk_cancel_dev(ub);
	return ret;
}

/*
 * 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;
}

/*
 * Lock for maple tree modification: acquire ub->mutex, then freeze queue
 * if device is started. If device is not yet started, only mutex is
 * needed since no I/O path can access the tree.
 *
 * This ordering (mutex -> freeze) is safe because ublk_stop_dev_unlocked()
 * already holds ub->mutex when calling del_gendisk() which freezes the queue.
*/
static unsigned int ublk_lock_buf_tree(struct ublk_device *ub)
{
	unsigned int memflags = 0;

	mutex_lock(&ub->mutex);
	if (ub->ub_disk)
		memflags = blk_mq_freeze_queue(ub->ub_disk->queue);

	return memflags;
}

static void ublk_unlock_buf_tree(struct ublk_device *ub, unsigned int memflags)
{
	if (ub->ub_disk)
		blk_mq_unfreeze_queue(ub->ub_disk->queue, memflags);
	mutex_unlock(&ub->mutex);
}

/* Erase coalesced PFN ranges from the maple tree matching buf_index */
static void ublk_buf_erase_ranges(struct ublk_device *ub, int buf_index)
{
	MA_STATE(mas, &ub->buf_tree, 0, ULONG_MAX);
	struct ublk_buf_range *range;

	mas_lock(&mas);
	mas_for_each(&mas, range, ULONG_MAX) {
		if (range->buf_index == buf_index) {
			mas_erase(&mas);
			kfree(range);
		}
	}
	mas_unlock(&mas);
}

static int __ublk_ctrl_reg_buf(struct ublk_device *ub,
			       struct page **pages, unsigned long nr_pages,
			       int index, unsigned short flags)
{
	unsigned long i;
	int ret;

	for (i = 0; i < nr_pages; i++) {
		unsigned long pfn = page_to_pfn(pages[i]);
		unsigned long start = i;
		struct ublk_buf_range *range;

		/* Find run of consecutive PFNs */
		while (i + 1 < nr_pages &&
		       page_to_pfn(pages[i + 1]) == pfn + (i - start) + 1)
			i++;

		range = kzalloc(sizeof(*range), GFP_KERNEL);
		if (!range) {
			ret = -ENOMEM;
			goto unwind;
		}
		range->buf_index = index;
		range->flags = flags;
		range->base_offset = start << PAGE_SHIFT;

		ret = mtree_insert_range(&ub->buf_tree, pfn,
					 pfn + (i - start),
					 range, GFP_KERNEL);
		if (ret) {
			kfree(range);
			goto unwind;
		}
	}
	return 0;

unwind:
	ublk_buf_erase_ranges(ub, index);
	return ret;
}

/*
 * Register a shared memory buffer for zero-copy I/O.
 * Pins pages, builds PFN maple tree, freezes/unfreezes the queue
 * internally. Returns buffer index (>= 0) on success.
 */
static int ublk_ctrl_reg_buf(struct ublk_device *ub,
			     struct ublksrv_ctrl_cmd *header)
{
	void __user *argp = (void __user *)(unsigned long)header->addr;
	struct ublk_shmem_buf_reg buf_reg;
	unsigned long nr_pages;
	struct page **pages = NULL;
	unsigned int gup_flags;
	unsigned int memflags;
	long pinned;
	int index;
	int ret;

	if (!ublk_dev_support_shmem_zc(ub))
		return -EOPNOTSUPP;

	memset(&buf_reg, 0, sizeof(buf_reg));
	if (copy_from_user(&buf_reg, argp,
			   min_t(size_t, header->len, sizeof(buf_reg))))
		return -EFAULT;

	if (buf_reg.flags & ~UBLK_SHMEM_BUF_READ_ONLY)
		return -EINVAL;

	if (buf_reg.reserved)
		return -EINVAL;

	if (!buf_reg.len || buf_reg.len > UBLK_SHMEM_BUF_SIZE_MAX ||
	    !PAGE_ALIGNED(buf_reg.len) || !PAGE_ALIGNED(buf_reg.addr))
		return -EINVAL;

	nr_pages = buf_reg.len >> PAGE_SHIFT;

	/* Pin pages before any locks (may sleep) */
	pages = kvmalloc_array(nr_pages, sizeof(*pages), GFP_KERNEL);
	if (!pages)
		return -ENOMEM;

	gup_flags = FOLL_LONGTERM;
	if (!(buf_reg.flags & UBLK_SHMEM_BUF_READ_ONLY))
		gup_flags |= FOLL_WRITE;

	pinned = pin_user_pages_fast(buf_reg.addr, nr_pages, gup_flags, pages);
	if (pinned < 0) {
		ret = pinned;
		goto err_free_pages;
	}
	if (pinned != nr_pages) {
		ret = -EFAULT;
		goto err_unpin;
	}

	memflags = ublk_lock_buf_tree(ub);

	index = ida_alloc_max(&ub->buf_ida, USHRT_MAX, GFP_KERNEL);
	if (index < 0) {
		ret = index;
		goto err_unlock;
	}

	ret = __ublk_ctrl_reg_buf(ub, pages, nr_pages, index, buf_reg.flags);
	if (ret) {
		ida_free(&ub->buf_ida, index);
		goto err_unlock;
	}

	ublk_unlock_buf_tree(ub, memflags);
	kvfree(pages);
	return index;

err_unlock:
	ublk_unlock_buf_tree(ub, memflags);
err_unpin:
	unpin_user_pages(pages, pinned);
err_free_pages:
	kvfree(pages);
	return ret;
}

static int __ublk_ctrl_unreg_buf(struct ublk_device *ub, int buf_index)
{
	MA_STATE(mas, &ub->buf_tree, 0, ULONG_MAX);
	struct ublk_buf_range *range;
	struct page *pages[32];
	int ret = -ENOENT;

	mas_lock(&mas);
	mas_for_each(&mas, range, ULONG_MAX) {
		unsigned long base, nr, off;

		if (range->buf_index != buf_index)
			continue;

		ret = 0;
		base = mas.index;
		nr = mas.last - base + 1;
		mas_erase(&mas);

		for (off = 0; off < nr; ) {
			unsigned int batch = min_t(unsigned long,
						   nr - off, 32);
			unsigned int j;

			for (j = 0; j < batch; j++)
				pages[j] = pfn_to_page(base + off + j);
			unpin_user_pages(pages, batch);
			off += batch;
		}
		kfree(range);
	}
	mas_unlock(&mas);

	return ret;
}

static int ublk_ctrl_unreg_buf(struct ublk_device *ub,
			       struct ublksrv_ctrl_cmd *header)
{
	int index = (int)header->data[0];
	unsigned int memflags;
	int ret;

	if (!ublk_dev_support_shmem_zc(ub))
		return -EOPNOTSUPP;

	if (index < 0 || index > USHRT_MAX)
		return -EINVAL;

	memflags = ublk_lock_buf_tree(ub);

	ret = __ublk_ctrl_unreg_buf(ub, index);
	if (!ret)
		ida_free(&ub->buf_ida, index);

	ublk_unlock_buf_tree(ub, memflags);
	return ret;
}

static void ublk_buf_cleanup(struct ublk_device *ub)
{
	MA_STATE(mas, &ub->buf_tree, 0, ULONG_MAX);
	struct ublk_buf_range *range;
	struct page *pages[32];

	mas_for_each(&mas, range, ULONG_MAX) {
		unsigned long base = mas.index;
		unsigned long nr = mas.last - base + 1;
		unsigned long off;

		for (off = 0; off < nr; ) {
			unsigned int batch = min_t(unsigned long,
						   nr - off, 32);
			unsigned int j;

			for (j = 0; j < batch; j++)
				pages[j] = pfn_to_page(base + off + j);
			unpin_user_pages(pages, batch);
			off += batch;
		}
		kfree(range);
	}
	mtree_destroy(&ub->buf_tree);
	ida_destroy(&ub->buf_ida);
}

/* Check if request pages match a registered shared memory buffer */
static bool ublk_try_buf_match(struct ublk_device *ub,
				   struct request *rq,
				   u32 *buf_idx, u32 *buf_off)
{
	struct req_iterator iter;
	struct bio_vec bv;
	int index = -1;
	unsigned long expected_offset = 0;
	bool first = true;

	rq_for_each_bvec(bv, rq, iter) {
		unsigned long pfn = page_to_pfn(bv.bv_page);
		unsigned long end_pfn = pfn +
			((bv.bv_offset + bv.bv_len - 1) >> PAGE_SHIFT);
		struct ublk_buf_range *range;
		unsigned long off;
		MA_STATE(mas, &ub->buf_tree, pfn, pfn);

		range = mas_walk(&mas);
		if (!range)
			return false;

		/* verify all pages in this bvec fall within the range */
		if (end_pfn > mas.last)
			return false;

		off = range->base_offset +
			(pfn - mas.index) * PAGE_SIZE + bv.bv_offset;

		if (first) {
			/* Read-only buffer can't serve READ (kernel writes) */
			if ((range->flags & UBLK_SHMEM_BUF_READ_ONLY) &&
			    req_op(rq) != REQ_OP_WRITE)
				return false;
			index = range->buf_index;
			expected_offset = off;
			*buf_off = off;
			first = false;
		} else {
			if (range->buf_index != index)
				return false;
			if (off != expected_offset)
				return false;
		}
		expected_offset += bv.bv_len;
	}

	if (first)
		return false;

	*buf_idx = index;
	return true;
}

static int ublk_ctrl_uring_cmd_permission(struct ublk_device *ub,
		u32 cmd_op, struct ublksrv_ctrl_cmd *header)
{
	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_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_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:
	case UBLK_CMD_UPDATE_SIZE:
	case UBLK_CMD_QUIESCE_DEV:
	case UBLK_CMD_TRY_STOP_DEV:
	case UBLK_CMD_REG_BUF:
	case UBLK_CMD_UNREG_BUF:
		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_op,
			ub->dev_info.owner_uid, ub->dev_info.owner_gid,
			dev_path, ret);
exit:
	kfree(dev_path);
	return ret;
}

static bool ublk_ctrl_uring_cmd_may_sleep(u32 cmd_op)
{
	switch (_IOC_NR(cmd_op)) {
	case UBLK_CMD_GET_QUEUE_AFFINITY:
	case UBLK_CMD_GET_DEV_INFO:
	case UBLK_CMD_GET_DEV_INFO2:
	case _IOC_NR(UBLK_U_CMD_GET_FEATURES):
		return false;
	default:
		return true;
	}
}

static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
		unsigned int issue_flags)
{
	/* May point to userspace-mapped memory */
	const struct ublksrv_ctrl_cmd *ub_src = io_uring_sqe128_cmd(cmd->sqe,
								    struct ublksrv_ctrl_cmd);
	struct ublksrv_ctrl_cmd header;
	struct ublk_device *ub = NULL;
	u32 cmd_op = cmd->cmd_op;
	int ret = -EINVAL;

	if (ublk_ctrl_uring_cmd_may_sleep(cmd_op) &&
	    issue_flags & IO_URING_F_NONBLOCK)
		return -EAGAIN;

	if (!(issue_flags & IO_URING_F_SQE128))
		return -EINVAL;

	header.dev_id = READ_ONCE(ub_src->dev_id);
	header.queue_id = READ_ONCE(ub_src->queue_id);
	header.len = READ_ONCE(ub_src->len);
	header.addr = READ_ONCE(ub_src->addr);
	header.data[0] = READ_ONCE(ub_src->data[0]);
	header.dev_path_len = READ_ONCE(ub_src->dev_path_len);
	ublk_ctrl_cmd_dump(cmd_op, &header);

	ret = ublk_check_cmd_op(cmd_op);
	if (ret)
		goto out;

	if (cmd_op == UBLK_U_CMD_GET_FEATURES) {
		ret = ublk_ctrl_get_features(&header);
		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_op, &header);
		if (ret)
			goto put_dev;
	}

	switch (_IOC_NR(cmd_op)) {
	case UBLK_CMD_START_DEV:
		ret = ublk_ctrl_start_dev(ub, &header);
		break;
	case UBLK_CMD_STOP_DEV:
		ublk_ctrl_stop_dev(ub);
		ret = 0;
		break;
	case UBLK_CMD_GET_DEV_INFO:
	case UBLK_CMD_GET_DEV_INFO2:
		ret = ublk_ctrl_get_dev_info(ub, &header);
		break;
	case UBLK_CMD_ADD_DEV:
		ret = ublk_ctrl_add_dev(&header);
		break;
	case UBLK_CMD_DEL_DEV:
		ret = ublk_ctrl_del_dev(&ub, true);
		break;
	case UBLK_CMD_DEL_DEV_ASYNC:
		ret = ublk_ctrl_del_dev(&ub, false);
		break;
	case UBLK_CMD_GET_QUEUE_AFFINITY:
		ret = ublk_ctrl_get_queue_affinity(ub, &header);
		break;
	case UBLK_CMD_GET_PARAMS:
		ret = ublk_ctrl_get_params(ub, &header);
		break;
	case UBLK_CMD_SET_PARAMS:
		ret = ublk_ctrl_set_params(ub, &header);
		break;
	case UBLK_CMD_START_USER_RECOVERY:
		ret = ublk_ctrl_start_recovery(ub);
		break;
	case UBLK_CMD_END_USER_RECOVERY:
		ret = ublk_ctrl_end_recovery(ub, &header);
		break;
	case UBLK_CMD_UPDATE_SIZE:
		ret = ublk_ctrl_set_size(ub, &header);
		break;
	case UBLK_CMD_QUIESCE_DEV:
		ret = ublk_ctrl_quiesce_dev(ub, &header);
		break;
	case UBLK_CMD_TRY_STOP_DEV:
		ret = ublk_ctrl_try_stop_dev(ub);
		break;
	case UBLK_CMD_REG_BUF:
		ret = ublk_ctrl_reg_buf(ub, &header);
		break;
	case UBLK_CMD_UNREG_BUF:
		ret = ublk_ctrl_unreg_buf(ub, &header);
		break;
	default:
		ret = -EOPNOTSUPP;
		break;
	}

 put_dev:
	if (ub)
		ublk_put_device(ub);
 out:
	pr_devel("%s: cmd done ret %d cmd_op %x, dev id %d qid %d\n",
			__func__, ret, cmd_op, header.dev_id, header.queue_id);
	return ret;
}

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);
	/*
	 * Ensure UBLKSRV_IO_BUF_OFFSET + UBLKSRV_IO_BUF_TOTAL_SIZE
	 * doesn't overflow into UBLKSRV_IO_INTEGRITY_FLAG
	 */
	BUILD_BUG_ON(UBLKSRV_IO_BUF_OFFSET + UBLKSRV_IO_BUF_TOTAL_SIZE >=
		     UBLKSRV_IO_INTEGRITY_FLAG);
	BUILD_BUG_ON(sizeof(struct ublk_auto_buf_reg) != 8);

	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);

static int ublk_set_max_unprivileged_ublks(const char *buf,
					   const struct kernel_param *kp)
{
	return param_set_uint_minmax(buf, kp, 0, UBLK_MAX_UBLKS);
}

static int ublk_get_max_unprivileged_ublks(char *buf,
					   const struct kernel_param *kp)
{
	return sysfs_emit(buf, "%u\n", unprivileged_ublks_max);
}

static const struct kernel_param_ops ublk_max_unprivileged_ublks_ops = {
	.set = ublk_set_max_unprivileged_ublks,
	.get = ublk_get_max_unprivileged_ublks,
};

module_param_cb(ublks_max, &ublk_max_unprivileged_ublks_ops,
		&unprivileged_ublks_max, 0644);
MODULE_PARM_DESC(ublks_max, "max number of unprivileged ublk devices allowed to add(default: 64)");

MODULE_AUTHOR("Ming Lei <ming.lei@redhat.com>");
MODULE_DESCRIPTION("Userspace block device");
MODULE_LICENSE("GPL");