linux/drivers/block/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.h>
#include <linux/blk-mq.h>
#include <linux/delay.h>
#include <linux/mm.h>
#include <asm/page.h>
#include <linux/task_work.h>
#include <uapi/linux/ublk_cmd.h>

#define UBLK_MINORS		(1U << MINORBITS)

struct ublk_rq_data {
	struct callback_head work;
};

struct ublk_uring_cmd_pdu {
	struct request *req;
};

/*
 * io command is active: sqe cmd is received, and its cqe isn't done
 *
 * If the flag is set, the io command is owned by ublk driver, and waited
 * for incoming blk-mq request from the ublk block device.
 *
 * If the flag is cleared, the io command will be completed, and owned by
 * ublk server.
 */
#define UBLK_IO_FLAG_ACTIVE	0x01

/*
 * IO command is completed via cqe, and it is being handled by ublksrv, and
 * not committed yet
 *
 * Basically exclusively with UBLK_IO_FLAG_ACTIVE, so can be served for
 * cross verification
 */
#define UBLK_IO_FLAG_OWNED_BY_SRV 0x02

/*
 * IO command is aborted, so this flag is set in case of
 * !UBLK_IO_FLAG_ACTIVE.
 *
 * After this flag is observed, any pending or new incoming request
 * associated with this io command will be failed immediately
 */
#define UBLK_IO_FLAG_ABORTED 0x04

struct ublk_io {
	/* userspace buffer address from io cmd */
	__u64	addr;
	unsigned int flags;
	int res;

	struct io_uring_cmd *cmd;
};

struct ublk_queue {
	int q_id;
	int q_depth;

	unsigned long flags;
	struct task_struct	*ubq_daemon;
	char *io_cmd_buf;

	unsigned long io_addr;	/* mapped vm address */
	unsigned int max_io_sz;
	bool abort_work_pending;
	unsigned short nr_io_ready;	/* how many ios setup */
	struct ublk_device *dev;
	struct ublk_io ios[0];
};

#define UBLK_DAEMON_MONITOR_PERIOD	(5 * HZ)

struct ublk_device {
	struct gendisk		*ub_disk;
	struct request_queue	*ub_queue;

	char	*__queues;

	unsigned short  queue_size;
	unsigned short  bs_shift;
	struct ublksrv_ctrl_dev_info	dev_info;

	struct blk_mq_tag_set	tag_set;

	struct cdev		cdev;
	struct device		cdev_dev;

	atomic_t		ch_open_cnt;
	int			ub_number;

	struct mutex		mutex;

	struct mm_struct	*mm;

	struct completion	completion;
	unsigned int		nr_queues_ready;
	atomic_t		nr_aborted_queues;

	/*
	 * Our ubq->daemon may be killed without any notification, so
	 * monitor each queue's daemon periodically
	 */
	struct delayed_work	monitor_work;
	struct work_struct	stop_work;
};

static dev_t ublk_chr_devt;
static struct class *ublk_chr_class;

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 miscdevice ublk_misc;

static inline bool ublk_can_use_task_work(const struct ublk_queue *ubq)
{
	if (IS_BUILTIN(CONFIG_BLK_DEV_UBLK) &&
			!(ubq->flags & UBLK_F_URING_CMD_COMP_IN_TASK))
		return true;
	return false;
}

static struct ublk_device *ublk_get_device(struct ublk_device *ub)
{
	if (kobject_get_unless_zero(&ub->cdev_dev.kobj))
		return ub;
	return NULL;
}

static void ublk_put_device(struct ublk_device *ub)
{
	put_device(&ub->cdev_dev);
}

static inline struct ublk_queue *ublk_get_queue(struct ublk_device *dev,
		int qid)
{
       return (struct ublk_queue *)&(dev->__queues[qid * dev->queue_size]);
}

static inline bool ublk_rq_has_data(const struct request *rq)
{
	return rq->bio && bio_has_data(rq->bio);
}

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

static inline char *ublk_queue_cmd_buf(struct ublk_device *ub, int q_id)
{
	return ublk_get_queue(ub, q_id)->io_cmd_buf;
}

static inline int ublk_queue_cmd_buf_size(struct ublk_device *ub, int q_id)
{
	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);

	return round_up(ubq->q_depth * sizeof(struct ublksrv_io_desc),
			PAGE_SIZE);
}

static int ublk_open(struct block_device *bdev, fmode_t mode)
{
	return 0;
}

static void ublk_release(struct gendisk *disk, fmode_t mode)
{
}

static const struct block_device_operations ub_fops = {
	.owner =	THIS_MODULE,
	.open =		ublk_open,
	.release =	ublk_release,
};

#define UBLK_MAX_PIN_PAGES	32

struct ublk_map_data {
	const struct ublk_queue *ubq;
	const struct request *rq;
	const struct ublk_io *io;
	unsigned max_bytes;
};

struct ublk_io_iter {
	struct page *pages[UBLK_MAX_PIN_PAGES];
	unsigned pg_off;	/* offset in the 1st page in pages */
	int nr_pages;		/* how many page pointers in pages */
	struct bio *bio;
	struct bvec_iter iter;
};

static inline unsigned ublk_copy_io_pages(struct ublk_io_iter *data,
		unsigned max_bytes, bool to_vm)
{
	const unsigned total = min_t(unsigned, max_bytes,
			PAGE_SIZE - data->pg_off +
			((data->nr_pages - 1) << PAGE_SHIFT));
	unsigned done = 0;
	unsigned pg_idx = 0;

	while (done < total) {
		struct bio_vec bv = bio_iter_iovec(data->bio, data->iter);
		const unsigned int bytes = min3(bv.bv_len, total - done,
				(unsigned)(PAGE_SIZE - data->pg_off));
		void *bv_buf = bvec_kmap_local(&bv);
		void *pg_buf = kmap_local_page(data->pages[pg_idx]);

		if (to_vm)
			memcpy(pg_buf + data->pg_off, bv_buf, bytes);
		else
			memcpy(bv_buf, pg_buf + data->pg_off, bytes);

		kunmap_local(pg_buf);
		kunmap_local(bv_buf);

		/* advance page array */
		data->pg_off += bytes;
		if (data->pg_off == PAGE_SIZE) {
			pg_idx += 1;
			data->pg_off = 0;
		}

		done += bytes;

		/* advance bio */
		bio_advance_iter_single(data->bio, &data->iter, bytes);
		if (!data->iter.bi_size) {
			data->bio = data->bio->bi_next;
			if (data->bio == NULL)
				break;
			data->iter = data->bio->bi_iter;
		}
	}

	return done;
}

static inline int ublk_copy_user_pages(struct ublk_map_data *data,
		bool to_vm)
{
	const unsigned int gup_flags = to_vm ? FOLL_WRITE : 0;
	const unsigned long start_vm = data->io->addr;
	unsigned int done = 0;
	struct ublk_io_iter iter = {
		.pg_off	= start_vm & (PAGE_SIZE - 1),
		.bio	= data->rq->bio,
		.iter	= data->rq->bio->bi_iter,
	};
	const unsigned int nr_pages = round_up(data->max_bytes +
			(start_vm & (PAGE_SIZE - 1)), PAGE_SIZE) >> PAGE_SHIFT;

	while (done < nr_pages) {
		const unsigned to_pin = min_t(unsigned, UBLK_MAX_PIN_PAGES,
				nr_pages - done);
		unsigned i, len;

		iter.nr_pages = get_user_pages_fast(start_vm +
				(done << PAGE_SHIFT), to_pin, gup_flags,
				iter.pages);
		if (iter.nr_pages <= 0)
			return done == 0 ? iter.nr_pages : done;
		len = ublk_copy_io_pages(&iter, data->max_bytes, to_vm);
		for (i = 0; i < iter.nr_pages; i++) {
			if (to_vm)
				set_page_dirty(iter.pages[i]);
			put_page(iter.pages[i]);
		}
		data->max_bytes -= len;
		done += iter.nr_pages;
	}

	return done;
}

static int ublk_map_io(const struct ublk_queue *ubq, const struct request *req,
		struct ublk_io *io)
{
	const unsigned int rq_bytes = blk_rq_bytes(req);
	/*
	 * 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 (req_op(req) != REQ_OP_WRITE && req_op(req) != REQ_OP_FLUSH)
		return rq_bytes;

	if (ublk_rq_has_data(req)) {
		struct ublk_map_data data = {
			.ubq	=	ubq,
			.rq	=	req,
			.io	=	io,
			.max_bytes =	rq_bytes,
		};

		ublk_copy_user_pages(&data, true);

		return rq_bytes - data.max_bytes;
	}
	return rq_bytes;
}

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

	if (req_op(req) == REQ_OP_READ && ublk_rq_has_data(req)) {
		struct ublk_map_data data = {
			.ubq	=	ubq,
			.rq	=	req,
			.io	=	io,
			.max_bytes =	io->res,
		};

		WARN_ON_ONCE(io->res > rq_bytes);

		ublk_copy_user_pages(&data, false);

		return io->res - data.max_bytes;
	}
	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_INTEGRITY)
		flags |= UBLK_IO_F_INTEGRITY;

	if (req->cmd_flags & REQ_FUA)
		flags |= UBLK_IO_F_FUA;

	if (req->cmd_flags & REQ_PREFLUSH)
		flags |= UBLK_IO_F_PREFLUSH;

	if (req->cmd_flags & REQ_NOUNMAP)
		flags |= UBLK_IO_F_NOUNMAP;

	if (req->cmd_flags & REQ_SWAP)
		flags |= UBLK_IO_F_SWAP;

	return flags;
}

static int 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:
		return BLK_STS_IOERR;
	}

	/* need to translate since kernel may change */
	iod->op_flags = ublk_op | ublk_req_build_flags(req);
	iod->nr_sectors = blk_rq_sectors(req);
	iod->start_sector = blk_rq_pos(req);
	iod->addr = io->addr;

	return BLK_STS_OK;
}

static inline struct ublk_uring_cmd_pdu *ublk_get_uring_cmd_pdu(
		struct io_uring_cmd *ioucmd)
{
	return (struct ublk_uring_cmd_pdu *)&ioucmd->pdu;
}

static bool ubq_daemon_is_dying(struct ublk_queue *ubq)
{
	return ubq->ubq_daemon->flags & PF_EXITING;
}

/* todo: handle partial completion */
static void ublk_complete_rq(struct request *req)
{
	struct ublk_queue *ubq = req->mq_hctx->driver_data;
	struct ublk_io *io = &ubq->ios[req->tag];
	unsigned int unmapped_bytes;

	/* failed read IO if nothing is read */
	if (!io->res && req_op(req) == REQ_OP_READ)
		io->res = -EIO;

	if (io->res < 0) {
		blk_mq_end_request(req, errno_to_blk_status(io->res));
		return;
	}

	/*
	 * FLUSH or DISCARD 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) {
		blk_mq_end_request(req, BLK_STS_OK);
		return;
	}

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

	/*
	 * Extremely impossible since we got data filled in just before
	 *
	 * Re-read simply for this unlikely case.
	 */
	if (unlikely(unmapped_bytes < io->res))
		io->res = unmapped_bytes;

	if (blk_update_request(req, BLK_STS_OK, io->res))
		blk_mq_requeue_request(req, true);
	else
		__blk_mq_end_request(req, BLK_STS_OK);
}

/*
 * __ublk_fail_req() may be called from abort context or ->ubq_daemon
 * context during exiting, so lock is required.
 *
 * Also aborting may not be started yet, keep in mind that one failed
 * request may be issued by block layer again.
 */
static void __ublk_fail_req(struct ublk_io *io, struct request *req)
{
	WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_ACTIVE);

	if (!(io->flags & UBLK_IO_FLAG_ABORTED)) {
		io->flags |= UBLK_IO_FLAG_ABORTED;
		blk_mq_end_request(req, BLK_STS_IOERR);
	}
}

#define UBLK_REQUEUE_DELAY_MS	3

static inline void __ublk_rq_task_work(struct request *req)
{
	struct ublk_queue *ubq = req->mq_hctx->driver_data;
	struct ublk_device *ub = ubq->dev;
	int tag = req->tag;
	struct ublk_io *io = &ubq->ios[tag];
	bool task_exiting = current != ubq->ubq_daemon ||
		(current->flags & PF_EXITING);
	unsigned int mapped_bytes;

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

	if (unlikely(task_exiting)) {
		blk_mq_end_request(req, BLK_STS_IOERR);
		mod_delayed_work(system_wq, &ub->monitor_work, 0);
		return;
	}

	mapped_bytes = ublk_map_io(ubq, req, io);

	/* partially mapped, update io descriptor */
	if (unlikely(mapped_bytes != blk_rq_bytes(req))) {
		/*
		 * Nothing mapped, retry until we succeed.
		 *
		 * We may never succeed in mapping any bytes here because
		 * of OOM. TODO: reserve one buffer with single page pinned
		 * for providing forward progress guarantee.
		 */
		if (unlikely(!mapped_bytes)) {
			blk_mq_requeue_request(req, false);
			blk_mq_delay_kick_requeue_list(req->q,
					UBLK_REQUEUE_DELAY_MS);
			return;
		}

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

	/* mark this cmd owned by ublksrv */
	io->flags |= UBLK_IO_FLAG_OWNED_BY_SRV;

	/*
	 * clear ACTIVE since we are done with this sqe/cmd slot
	 * We can only accept io cmd in case of being not active.
	 */
	io->flags &= ~UBLK_IO_FLAG_ACTIVE;

	/* tell ublksrv one io request is coming */
	io_uring_cmd_done(io->cmd, UBLK_IO_RES_OK, 0);
}

static void ublk_rq_task_work_cb(struct io_uring_cmd *cmd)
{
	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);

	__ublk_rq_task_work(pdu->req);
}

static void ublk_rq_task_work_fn(struct callback_head *work)
{
	struct ublk_rq_data *data = container_of(work,
			struct ublk_rq_data, work);
	struct request *req = blk_mq_rq_from_pdu(data);

	__ublk_rq_task_work(req);
}

static blk_status_t ublk_queue_rq(struct blk_mq_hw_ctx *hctx,
		const struct blk_mq_queue_data *bd)
{
	struct ublk_queue *ubq = hctx->driver_data;
	struct request *rq = bd->rq;
	blk_status_t res;

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

	blk_mq_start_request(bd->rq);

	if (unlikely(ubq_daemon_is_dying(ubq))) {
 fail:
		mod_delayed_work(system_wq, &ubq->dev->monitor_work, 0);
		return BLK_STS_IOERR;
	}

	if (ublk_can_use_task_work(ubq)) {
		struct ublk_rq_data *data = blk_mq_rq_to_pdu(rq);
		enum task_work_notify_mode notify_mode = bd->last ?
			TWA_SIGNAL_NO_IPI : TWA_NONE;

		if (task_work_add(ubq->ubq_daemon, &data->work, notify_mode))
			goto fail;
	} else {
		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_rq_task_work_cb);
	}

	return BLK_STS_OK;
}

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

	if (ublk_can_use_task_work(ubq))
		__set_notify_signal(ubq->ubq_daemon);
}

static int ublk_init_hctx(struct blk_mq_hw_ctx *hctx, void *driver_data,
		unsigned int hctx_idx)
{
	struct ublk_device *ub = hctx->queue->queuedata;
	struct ublk_queue *ubq = ublk_get_queue(ub, hctx->queue_num);

	hctx->driver_data = ubq;
	return 0;
}

static int ublk_init_rq(struct blk_mq_tag_set *set, struct request *req,
		unsigned int hctx_idx, unsigned int numa_node)
{
	struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);

	init_task_work(&data->work, ublk_rq_task_work_fn);
	return 0;
}

static const struct blk_mq_ops ublk_mq_ops = {
	.queue_rq       = ublk_queue_rq,
	.commit_rqs     = ublk_commit_rqs,
	.init_hctx	= ublk_init_hctx,
	.init_request   = ublk_init_rq,
};

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 (atomic_cmpxchg(&ub->ch_open_cnt, 0, 1) == 0) {
		filp->private_data = ub;
		return 0;
	}
	return -EBUSY;
}

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

	while (atomic_cmpxchg(&ub->ch_open_cnt, 1, 0) != 1)
		cpu_relax();

	filp->private_data = NULL;
	return 0;
}

/* map pre-allocated per-queue cmd buffer to ublksrv daemon */
static int ublk_ch_mmap(struct file *filp, struct vm_area_struct *vma)
{
	struct ublk_device *ub = filp->private_data;
	size_t sz = vma->vm_end - vma->vm_start;
	unsigned max_sz = UBLK_MAX_QUEUE_DEPTH * sizeof(struct ublksrv_io_desc);
	unsigned long pfn, end, phys_off = vma->vm_pgoff << PAGE_SHIFT;
	int q_id, ret = 0;

	mutex_lock(&ub->mutex);
	if (!ub->mm)
		ub->mm = current->mm;
	if (current->mm != ub->mm)
		ret = -EINVAL;
	mutex_unlock(&ub->mutex);

	if (ret)
		return ret;

	if (vma->vm_flags & VM_WRITE)
		return -EPERM;

	end = UBLKSRV_CMD_BUF_OFFSET + ub->dev_info.nr_hw_queues * max_sz;
	if (phys_off < UBLKSRV_CMD_BUF_OFFSET || phys_off >= end)
		return -EINVAL;

	q_id = (phys_off - UBLKSRV_CMD_BUF_OFFSET) / max_sz;
	pr_devel("%s: qid %d, pid %d, addr %lx pg_off %lx sz %lu\n",
			__func__, q_id, current->pid, vma->vm_start,
			phys_off, (unsigned long)sz);

	if (sz != ublk_queue_cmd_buf_size(ub, q_id))
		return -EINVAL;

	pfn = virt_to_phys(ublk_queue_cmd_buf(ub, q_id)) >> PAGE_SHIFT;
	return remap_pfn_range(vma, vma->vm_start, pfn, sz, vma->vm_page_prot);
}

static void ublk_commit_completion(struct ublk_device *ub,
		struct ublksrv_io_cmd *ub_cmd)
{
	u32 qid = ub_cmd->q_id, tag = ub_cmd->tag;
	struct ublk_queue *ubq = ublk_get_queue(ub, qid);
	struct ublk_io *io = &ubq->ios[tag];
	struct request *req;

	/* now this cmd slot is owned by nbd driver */
	io->flags &= ~UBLK_IO_FLAG_OWNED_BY_SRV;
	io->res = ub_cmd->result;

	/* find the io request and complete */
	req = blk_mq_tag_to_rq(ub->tag_set.tags[qid], tag);

	if (req && likely(!blk_should_fake_timeout(req->q)))
		ublk_complete_rq(req);
}

/*
 * When ->ubq_daemon is exiting, either new request is ended immediately,
 * or any queued io command is drained, so it is safe to abort queue
 * lockless
 */
static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq)
{
	int i;

	if (!ublk_get_device(ub))
		return;

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

		if (!(io->flags & UBLK_IO_FLAG_ACTIVE)) {
			struct request *rq;

			/*
			 * Either we fail the request or ublk_rq_task_work_fn
			 * will do it
			 */
			rq = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], i);
			if (rq)
				__ublk_fail_req(io, rq);
		}
	}
	ublk_put_device(ub);
}

static void ublk_daemon_monitor_work(struct work_struct *work)
{
	struct ublk_device *ub =
		container_of(work, struct ublk_device, monitor_work.work);
	int i;

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

		if (ubq_daemon_is_dying(ubq)) {
			schedule_work(&ub->stop_work);

			/* abort queue is for making forward progress */
			ublk_abort_queue(ub, ubq);
		}
	}

	/*
	 * We can't schedule monitor work after ublk_remove() is started.
	 *
	 * No need ub->mutex, monitor work are canceled after state is marked
	 * as DEAD, so DEAD state is observed reliably.
	 */
	if (ub->dev_info.state != UBLK_S_DEV_DEAD)
		schedule_delayed_work(&ub->monitor_work,
				UBLK_DAEMON_MONITOR_PERIOD);
}

static void ublk_cancel_queue(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_ACTIVE)
			io_uring_cmd_done(io->cmd, UBLK_IO_RES_ABORT, 0);
	}
}

/* Cancel all pending commands, must be called after del_gendisk() returns */
static void ublk_cancel_dev(struct ublk_device *ub)
{
	int i;

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

static void ublk_stop_dev(struct ublk_device *ub)
{
	mutex_lock(&ub->mutex);
	if (!disk_live(ub->ub_disk))
		goto unlock;

	del_gendisk(ub->ub_disk);
	ub->dev_info.state = UBLK_S_DEV_DEAD;
	ub->dev_info.ublksrv_pid = -1;
	ublk_cancel_dev(ub);
 unlock:
	mutex_unlock(&ub->mutex);
	cancel_delayed_work_sync(&ub->monitor_work);
}

static int ublk_ctrl_stop_dev(struct ublk_device *ub)
{
	ublk_stop_dev(ub);
	cancel_work_sync(&ub->stop_work);
	return 0;
}

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

/* device can only be started after all IOs are ready */
static void ublk_mark_io_ready(struct ublk_device *ub, struct ublk_queue *ubq)
{
	mutex_lock(&ub->mutex);
	ubq->nr_io_ready++;
	if (ublk_queue_ready(ubq)) {
		ubq->ubq_daemon = current;
		get_task_struct(ubq->ubq_daemon);
		ub->nr_queues_ready++;
	}
	if (ub->nr_queues_ready == ub->dev_info.nr_hw_queues)
		complete_all(&ub->completion);
	mutex_unlock(&ub->mutex);
}

static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
{
	struct ublksrv_io_cmd *ub_cmd = (struct ublksrv_io_cmd *)cmd->cmd;
	struct ublk_device *ub = cmd->file->private_data;
	struct ublk_queue *ubq;
	struct ublk_io *io;
	u32 cmd_op = cmd->cmd_op;
	unsigned tag = ub_cmd->tag;
	int ret = -EINVAL;

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

	if (!(issue_flags & IO_URING_F_SQE128))
		goto out;

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

	ubq = ublk_get_queue(ub, ub_cmd->q_id);
	if (!ubq || ub_cmd->q_id != ubq->q_id)
		goto out;

	if (ubq->ubq_daemon && ubq->ubq_daemon != current)
		goto out;

	if (tag >= ubq->q_depth)
		goto out;

	io = &ubq->ios[tag];

	/* there is pending io cmd, something must be wrong */
	if (io->flags & UBLK_IO_FLAG_ACTIVE) {
		ret = -EBUSY;
		goto out;
	}

	switch (cmd_op) {
	case UBLK_IO_FETCH_REQ:
		/* UBLK_IO_FETCH_REQ is only allowed before queue is setup */
		if (ublk_queue_ready(ubq)) {
			ret = -EBUSY;
			goto out;
		}
		/*
		 * The io is being handled by server, so COMMIT_RQ is expected
		 * instead of FETCH_REQ
		 */
		if (io->flags & UBLK_IO_FLAG_OWNED_BY_SRV)
			goto out;
		/* FETCH_RQ has to provide IO buffer */
		if (!ub_cmd->addr)
			goto out;
		io->cmd = cmd;
		io->flags |= UBLK_IO_FLAG_ACTIVE;
		io->addr = ub_cmd->addr;

		ublk_mark_io_ready(ub, ubq);
		break;
	case UBLK_IO_COMMIT_AND_FETCH_REQ:
		/* FETCH_RQ has to provide IO buffer */
		if (!ub_cmd->addr)
			goto out;
		if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
			goto out;
		io->addr = ub_cmd->addr;
		io->flags |= UBLK_IO_FLAG_ACTIVE;
		io->cmd = cmd;
		ublk_commit_completion(ub, ub_cmd);
		break;
	default:
		goto out;
	}
	return -EIOCBQUEUED;

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

static const struct file_operations ublk_ch_fops = {
	.owner = THIS_MODULE,
	.open = ublk_ch_open,
	.release = ublk_ch_release,
	.llseek = no_llseek,
	.uring_cmd = ublk_ch_uring_cmd,
	.mmap = ublk_ch_mmap,
};

static void ublk_deinit_queue(struct ublk_device *ub, int q_id)
{
	int size = ublk_queue_cmd_buf_size(ub, q_id);
	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);

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

static int ublk_init_queue(struct ublk_device *ub, int q_id)
{
	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);
	gfp_t gfp_flags = GFP_KERNEL | __GFP_ZERO;
	void *ptr;
	int size;

	ubq->flags = ub->dev_info.flags[0];
	ubq->q_id = q_id;
	ubq->q_depth = ub->dev_info.queue_depth;
	size = ublk_queue_cmd_buf_size(ub, q_id);

	ptr = (void *) __get_free_pages(gfp_flags, get_order(size));
	if (!ptr)
		return -ENOMEM;

	ubq->io_cmd_buf = ptr;
	ubq->dev = ub;
	return 0;
}

static void ublk_deinit_queues(struct ublk_device *ub)
{
	int nr_queues = ub->dev_info.nr_hw_queues;
	int i;

	if (!ub->__queues)
		return;

	for (i = 0; i < nr_queues; i++)
		ublk_deinit_queue(ub, i);
	kfree(ub->__queues);
}

static int ublk_init_queues(struct ublk_device *ub)
{
	int nr_queues = ub->dev_info.nr_hw_queues;
	int depth = ub->dev_info.queue_depth;
	int ubq_size = sizeof(struct ublk_queue) + depth * sizeof(struct ublk_io);
	int i, ret = -ENOMEM;

	ub->queue_size = ubq_size;
	ub->__queues = kcalloc(nr_queues, ubq_size, GFP_KERNEL);
	if (!ub->__queues)
		return ret;

	for (i = 0; i < nr_queues; i++) {
		if (ublk_init_queue(ub, i))
			goto fail;
	}

	init_completion(&ub->completion);
	return 0;

 fail:
	ublk_deinit_queues(ub);
	return ret;
}

static int __ublk_alloc_dev_number(struct ublk_device *ub, int idx)
{
	int i = idx;
	int err;

	spin_lock(&ublk_idr_lock);
	/* allocate id, if @id >= 0, we're requesting that specific id */
	if (i >= 0) {
		err = idr_alloc(&ublk_index_idr, ub, i, i + 1, GFP_NOWAIT);
		if (err == -ENOSPC)
			err = -EEXIST;
	} else {
		err = idr_alloc(&ublk_index_idr, ub, 0, 0, GFP_NOWAIT);
	}
	spin_unlock(&ublk_idr_lock);

	if (err >= 0)
		ub->ub_number = err;

	return err;
}

static struct ublk_device *__ublk_create_dev(int idx)
{
	struct ublk_device *ub = NULL;
	int ret;

	ub = kzalloc(sizeof(*ub), GFP_KERNEL);
	if (!ub)
		return ERR_PTR(-ENOMEM);

	ret = __ublk_alloc_dev_number(ub, idx);
	if (ret < 0) {
		kfree(ub);
		return ERR_PTR(ret);
	}
	return ub;
}

static void __ublk_destroy_dev(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);

	mutex_destroy(&ub->mutex);

	kfree(ub);
}

static void ublk_cdev_rel(struct device *dev)
{
	struct ublk_device *ub = container_of(dev, struct ublk_device, cdev_dev);

	put_disk(ub->ub_disk);

	blk_mq_free_tag_set(&ub->tag_set);

	ublk_deinit_queues(ub);

	__ublk_destroy_dev(ub);
}

static int ublk_add_chdev(struct ublk_device *ub)
{
	struct device *dev = &ub->cdev_dev;
	int minor = ub->ub_number;
	int ret;

	dev->parent = ublk_misc.this_device;
	dev->devt = MKDEV(MAJOR(ublk_chr_devt), minor);
	dev->class = ublk_chr_class;
	dev->release = ublk_cdev_rel;
	device_initialize(dev);

	ret = dev_set_name(dev, "ublkc%d", minor);
	if (ret)
		goto fail;

	cdev_init(&ub->cdev, &ublk_ch_fops);
	ret = cdev_device_add(&ub->cdev, dev);
	if (ret)
		goto fail;
	return 0;
 fail:
	put_device(dev);
	return ret;
}

static void ublk_stop_work_fn(struct work_struct *work)
{
	struct ublk_device *ub =
		container_of(work, struct ublk_device, stop_work);

	ublk_stop_dev(ub);
}

static void ublk_update_capacity(struct ublk_device *ub)
{
	unsigned int max_rq_bytes;

	/* make max request buffer size aligned with PAGE_SIZE */
	max_rq_bytes = round_down(ub->dev_info.rq_max_blocks <<
			ub->bs_shift, PAGE_SIZE);
	ub->dev_info.rq_max_blocks = max_rq_bytes >> ub->bs_shift;

	set_capacity(ub->ub_disk, ub->dev_info.dev_blocks << (ub->bs_shift - 9));
}

/* add disk & cdev, cleanup everything in case of failure */
static int ublk_add_dev(struct ublk_device *ub)
{
	struct gendisk *disk;
	int err = -ENOMEM;
	int bsize;

	/* We are not ready to support zero copy */
	ub->dev_info.flags[0] &= ~UBLK_F_SUPPORT_ZERO_COPY;

	bsize = ub->dev_info.block_size;
	ub->bs_shift = ilog2(bsize);

	ub->dev_info.nr_hw_queues = min_t(unsigned int,
			ub->dev_info.nr_hw_queues, nr_cpu_ids);

	INIT_WORK(&ub->stop_work, ublk_stop_work_fn);
	INIT_DELAYED_WORK(&ub->monitor_work, ublk_daemon_monitor_work);

	if (ublk_init_queues(ub))
		goto out_destroy_dev;

	ub->tag_set.ops = &ublk_mq_ops;
	ub->tag_set.nr_hw_queues = ub->dev_info.nr_hw_queues;
	ub->tag_set.queue_depth = ub->dev_info.queue_depth;
	ub->tag_set.numa_node = NUMA_NO_NODE;
	ub->tag_set.cmd_size = sizeof(struct ublk_rq_data);
	ub->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
	ub->tag_set.driver_data = ub;

	err = blk_mq_alloc_tag_set(&ub->tag_set);
	if (err)
		goto out_deinit_queues;

	disk = ub->ub_disk = blk_mq_alloc_disk(&ub->tag_set, ub);
	if (IS_ERR(disk)) {
		err = PTR_ERR(disk);
		goto out_cleanup_tags;
	}
	ub->ub_queue = ub->ub_disk->queue;

	ub->ub_queue->queuedata = ub;

	blk_queue_logical_block_size(ub->ub_queue, bsize);
	blk_queue_physical_block_size(ub->ub_queue, bsize);
	blk_queue_io_min(ub->ub_queue, bsize);

	blk_queue_max_hw_sectors(ub->ub_queue, ub->dev_info.rq_max_blocks <<
			(ub->bs_shift - 9));

	ub->ub_queue->limits.discard_granularity = PAGE_SIZE;

	blk_queue_max_discard_sectors(ub->ub_queue, UINT_MAX >> 9);
	blk_queue_max_write_zeroes_sectors(ub->ub_queue, UINT_MAX >> 9);

	ublk_update_capacity(ub);

	disk->fops		= &ub_fops;
	disk->private_data	= ub;
	disk->queue		= ub->ub_queue;
	sprintf(disk->disk_name, "ublkb%d", ub->ub_number);

	mutex_init(&ub->mutex);

	/* add char dev so that ublksrv daemon can be setup */
	err = ublk_add_chdev(ub);
	if (err)
		return err;

	/* don't expose disk now until we got start command from cdev */

	return 0;

out_cleanup_tags:
	blk_mq_free_tag_set(&ub->tag_set);
out_deinit_queues:
	ublk_deinit_queues(ub);
out_destroy_dev:
	__ublk_destroy_dev(ub);
	return err;
}

static void ublk_remove(struct ublk_device *ub)
{
	ublk_ctrl_stop_dev(ub);

	cdev_device_del(&ub->cdev, &ub->cdev_dev);
	put_device(&ub->cdev_dev);
}

static struct ublk_device *ublk_get_device_from_id(int idx)
{
	struct ublk_device *ub = NULL;

	if (idx < 0)
		return NULL;

	spin_lock(&ublk_idr_lock);
	ub = idr_find(&ublk_index_idr, idx);
	if (ub)
		ub = ublk_get_device(ub);
	spin_unlock(&ublk_idr_lock);

	return ub;
}

static int ublk_ctrl_start_dev(struct ublk_device *ub, struct io_uring_cmd *cmd)
{
	struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
	int ret = -EINVAL;
	int ublksrv_pid = (int)header->data[0];
	unsigned long dev_blocks = header->data[1];

	if (ublksrv_pid <= 0)
		return ret;

	wait_for_completion_interruptible(&ub->completion);

	schedule_delayed_work(&ub->monitor_work, UBLK_DAEMON_MONITOR_PERIOD);

	mutex_lock(&ub->mutex);
	if (!disk_live(ub->ub_disk)) {
		/* We may get disk size updated */
		if (dev_blocks) {
			ub->dev_info.dev_blocks = dev_blocks;
			ublk_update_capacity(ub);
		}
		ub->dev_info.ublksrv_pid = ublksrv_pid;
		ret = add_disk(ub->ub_disk);
		if (!ret)
			ub->dev_info.state = UBLK_S_DEV_LIVE;
	} else {
		ret = -EEXIST;
	}
	mutex_unlock(&ub->mutex);

	return ret;
}

static struct blk_mq_hw_ctx *ublk_get_hw_queue(struct ublk_device *ub,
		unsigned int index)
{
	struct blk_mq_hw_ctx *hctx;
	unsigned long i;

	queue_for_each_hw_ctx(ub->ub_queue, hctx, i)
		if (hctx->queue_num == index)
			return hctx;
	return NULL;
}

static int ublk_ctrl_get_queue_affinity(struct io_uring_cmd *cmd)
{
	struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
	void __user *argp = (void __user *)(unsigned long)header->addr;
	struct blk_mq_hw_ctx *hctx;
	struct ublk_device *ub;
	unsigned long queue;
	unsigned int retlen;
	int ret;

	ub = ublk_get_device_from_id(header->dev_id);
	if (!ub)
		goto out;

	ret = -EINVAL;
	queue = header->data[0];
	if (queue >= ub->dev_info.nr_hw_queues)
		goto out;
	hctx = ublk_get_hw_queue(ub, queue);
	if (!hctx)
		goto out;

	retlen = min_t(unsigned short, header->len, cpumask_size());
	if (copy_to_user(argp, hctx->cpumask, retlen)) {
		ret = -EFAULT;
		goto out;
	}
	if (retlen != header->len) {
		if (clear_user(argp + retlen, header->len - retlen)) {
			ret = -EFAULT;
			goto out;
		}
	}
	ret = 0;
 out:
	if (ub)
		ublk_put_device(ub);
	return ret;
}

static int ublk_ctrl_add_dev(const struct ublksrv_ctrl_dev_info *info,
		void __user *argp, int idx)
{
	struct ublk_device *ub;
	int ret;

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

	ub = __ublk_create_dev(idx);
	if (!IS_ERR_OR_NULL(ub)) {
		memcpy(&ub->dev_info, info, sizeof(*info));

		/* update device id */
		ub->dev_info.dev_id = ub->ub_number;

		ret = ublk_add_dev(ub);
		if (!ret) {
			if (copy_to_user(argp, &ub->dev_info, sizeof(*info))) {
				ublk_remove(ub);
				ret = -EFAULT;
			}
		}
	} else {
		if (IS_ERR(ub))
			ret = PTR_ERR(ub);
		else
			ret = -ENOMEM;
	}
	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(int idx)
{
	struct ublk_device *ub;
	int ret;

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

	ub = ublk_get_device_from_id(idx);
	if (ub) {
		ublk_remove(ub);
		ublk_put_device(ub);
		ret = 0;
	} else {
		ret = -ENODEV;
	}

	/*
	 * Wait until the idr is removed, then it can be reused after
	 * DEL_DEV command is returned.
	 */
	if (!ret)
		wait_event(ublk_idr_wq, ublk_idr_freed(idx));
	mutex_unlock(&ublk_ctl_mutex);

	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[0]);
	pr_devel("\t nr_hw_queues %d queue_depth %d block size %d dev_capacity %lld\n",
			info->nr_hw_queues, info->queue_depth,
			info->block_size, info->dev_blocks);
}

static inline void ublk_ctrl_cmd_dump(struct io_uring_cmd *cmd)
{
	struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;

	pr_devel("%s: cmd_op %x, dev id %d qid %d data %llx buf %llx len %u\n",
			__func__, cmd->cmd_op, header->dev_id, header->queue_id,
			header->data[0], header->addr, header->len);
}

static int ublk_ctrl_cmd_validate(struct io_uring_cmd *cmd,
		struct ublksrv_ctrl_dev_info *info)
{
	struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
	u32 cmd_op = cmd->cmd_op;
	void __user *argp = (void __user *)(unsigned long)header->addr;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	switch (cmd_op) {
	case UBLK_CMD_GET_DEV_INFO:
		if (header->len < sizeof(*info) || !header->addr)
			return -EINVAL;
		break;
	case UBLK_CMD_ADD_DEV:
		if (header->len < sizeof(*info) || !header->addr)
			return -EINVAL;
		if (copy_from_user(info, argp, sizeof(*info)) != 0)
			return -EFAULT;
		ublk_dump_dev_info(info);
		if (header->dev_id != info->dev_id) {
			printk(KERN_WARNING "%s: cmd %x, dev id not match %u %u\n",
					__func__, cmd_op, header->dev_id,
					info->dev_id);
			return -EINVAL;
		}
		if (header->queue_id != (u16)-1) {
			printk(KERN_WARNING "%s: cmd %x queue_id is wrong %x\n",
					__func__, cmd_op, header->queue_id);
			return -EINVAL;
		}
		break;
	case UBLK_CMD_GET_QUEUE_AFFINITY:
		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;
	};

	return 0;
}

static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
		unsigned int issue_flags)
{
	struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
	void __user *argp = (void __user *)(unsigned long)header->addr;
	struct ublksrv_ctrl_dev_info info;
	u32 cmd_op = cmd->cmd_op;
	struct ublk_device *ub;
	int ret = -EINVAL;

	ublk_ctrl_cmd_dump(cmd);

	if (!(issue_flags & IO_URING_F_SQE128))
		goto out;

	ret = ublk_ctrl_cmd_validate(cmd, &info);
	if (ret)
		goto out;

	ret = -ENODEV;
	switch (cmd_op) {
	case UBLK_CMD_START_DEV:
		ub = ublk_get_device_from_id(header->dev_id);
		if (ub) {
			ret = ublk_ctrl_start_dev(ub, cmd);
			ublk_put_device(ub);
		}
		break;
	case UBLK_CMD_STOP_DEV:
		ub = ublk_get_device_from_id(header->dev_id);
		if (ub) {
			ret = ublk_ctrl_stop_dev(ub);
			ublk_put_device(ub);
		}
		break;
	case UBLK_CMD_GET_DEV_INFO:
		ub = ublk_get_device_from_id(header->dev_id);
		if (ub) {
			if (copy_to_user(argp, &ub->dev_info, sizeof(info)))
				ret = -EFAULT;
			else
				ret = 0;
			ublk_put_device(ub);
		}
		break;
	case UBLK_CMD_ADD_DEV:
		ret = ublk_ctrl_add_dev(&info, argp, header->dev_id);
		break;
	case UBLK_CMD_DEL_DEV:
		ret = ublk_ctrl_del_dev(header->dev_id);
		break;
	case UBLK_CMD_GET_QUEUE_AFFINITY:
		ret = ublk_ctrl_get_queue_affinity(cmd);
		break;
	default:
		break;
	};
 out:
	io_uring_cmd_done(cmd, ret, 0);
	pr_devel("%s: cmd done ret %d cmd_op %x, dev id %d qid %d\n",
			__func__, ret, cmd->cmd_op, header->dev_id, header->queue_id);
	return -EIOCBQUEUED;
}

static const struct file_operations ublk_ctl_fops = {
	.open		= nonseekable_open,
	.uring_cmd      = ublk_ctrl_uring_cmd,
	.owner		= THIS_MODULE,
	.llseek		= noop_llseek,
};

static struct miscdevice ublk_misc = {
	.minor		= MISC_DYNAMIC_MINOR,
	.name		= "ublk-control",
	.fops		= &ublk_ctl_fops,
};

static int __init ublk_init(void)
{
	int ret;

	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;

	ublk_chr_class = class_create(THIS_MODULE, "ublk-char");
	if (IS_ERR(ublk_chr_class)) {
		ret = PTR_ERR(ublk_chr_class);
		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;

	class_destroy(ublk_chr_class);

	misc_deregister(&ublk_misc);

	idr_for_each_entry(&ublk_index_idr, ub, id)
		ublk_remove(ub);

	idr_destroy(&ublk_index_idr);
	unregister_chrdev_region(ublk_chr_devt, UBLK_MINORS);
}

module_init(ublk_init);
module_exit(ublk_exit);

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