[thirdparty/linux.git] / 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 <linux/namei.h>
#include <uapi/linux/ublk_cmd.h>

#define UBLK_MINORS             (1U << MINORBITS)

/* All UBLK_F_* have to be included into UBLK_F_ALL */
#define UBLK_F_ALL (UBLK_F_SUPPORT_ZERO_COPY \
                | UBLK_F_URING_CMD_COMP_IN_TASK \
                | UBLK_F_NEED_GET_DATA \
                | UBLK_F_USER_RECOVERY \
                | UBLK_F_USER_RECOVERY_REISSUE \
                | UBLK_F_UNPRIVILEGED_DEV)

/* 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)

struct ublk_rq_data {
        struct llist_node node;
        struct callback_head work;
};

struct ublk_uring_cmd_pdu {
        struct ublk_queue *ubq;
};

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

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

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

/*
 * UBLK_IO_FLAG_NEED_GET_DATA is set because IO command requires
 * get data buffer address from ublksrv.
 *
 * Then, bio data could be copied into this data buffer for a WRITE request
 * after the IO command is issued again and UBLK_IO_FLAG_NEED_GET_DATA is unset.
 */
#define UBLK_IO_FLAG_NEED_GET_DATA 0x08

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

        struct io_uring_cmd *cmd;
};

struct ublk_queue {
        int q_id;
        int q_depth;

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

        struct llist_head       io_cmds;

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

#define UBLK_DAEMON_MONITOR_PERIOD      (5 * HZ)

struct ublk_device {
        struct gendisk          *ub_disk;

        char    *__queues;

        unsigned int    queue_size;
        struct ublksrv_ctrl_dev_info    dev_info;

        struct blk_mq_tag_set   tag_set;

        struct cdev             cdev;
        struct device           cdev_dev;

#define UB_STATE_OPEN           0
#define UB_STATE_USED           1
#define UB_STATE_DELETED        2
        unsigned long           state;
        int                     ub_number;

        struct mutex            mutex;

        spinlock_t              mm_lock;
        struct mm_struct        *mm;

        struct ublk_params      params;

        struct completion       completion;
        unsigned int            nr_queues_ready;
        unsigned int            nr_privileged_daemon;

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

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

static 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);

/*
 * Max ublk devices allowed to add
 *
 * It can be extended to one per-user limit in future or even controlled
 * by cgroup.
 */
static unsigned int ublks_max = 64;
static unsigned int ublks_added;        /* protected by ublk_ctl_mutex */

static struct miscdevice ublk_misc;

static void ublk_dev_param_basic_apply(struct ublk_device *ub)
{
        struct request_queue *q = ub->ub_disk->queue;
        const struct ublk_param_basic *p = &ub->params.basic;

        blk_queue_logical_block_size(q, 1 << p->logical_bs_shift);
        blk_queue_physical_block_size(q, 1 << p->physical_bs_shift);
        blk_queue_io_min(q, 1 << p->io_min_shift);
        blk_queue_io_opt(q, 1 << p->io_opt_shift);

        blk_queue_write_cache(q, p->attrs & UBLK_ATTR_VOLATILE_CACHE,
                        p->attrs & UBLK_ATTR_FUA);
        if (p->attrs & UBLK_ATTR_ROTATIONAL)
                blk_queue_flag_clear(QUEUE_FLAG_NONROT, q);
        else
                blk_queue_flag_set(QUEUE_FLAG_NONROT, q);

        blk_queue_max_hw_sectors(q, p->max_sectors);
        blk_queue_chunk_sectors(q, p->chunk_sectors);
        blk_queue_virt_boundary(q, p->virt_boundary_mask);

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

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

static void ublk_dev_param_discard_apply(struct ublk_device *ub)
{
        struct request_queue *q = ub->ub_disk->queue;
        const struct ublk_param_discard *p = &ub->params.discard;

        q->limits.discard_alignment = p->discard_alignment;
        q->limits.discard_granularity = p->discard_granularity;
        blk_queue_max_discard_sectors(q, p->max_discard_sectors);
        blk_queue_max_write_zeroes_sectors(q,
                        p->max_write_zeroes_sectors);
        blk_queue_max_discard_segments(q, p->max_discard_segments);
}

static int ublk_validate_params(const struct ublk_device *ub)
{
        /* basic param is the only one which must be set */
        if (ub->params.types & UBLK_PARAM_TYPE_BASIC) {
                const struct ublk_param_basic *p = &ub->params.basic;

                if (p->logical_bs_shift > PAGE_SHIFT)
                        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;
        } 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;

        return 0;
}

static int ublk_apply_params(struct ublk_device *ub)
{
        if (!(ub->params.types & UBLK_PARAM_TYPE_BASIC))
                return -EINVAL;

        ublk_dev_param_basic_apply(ub);

        if (ub->params.types & UBLK_PARAM_TYPE_DISCARD)
                ublk_dev_param_discard_apply(ub);

        return 0;
}

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 inline bool ublk_need_get_data(const struct ublk_queue *ubq)
{
        if (ubq->flags & UBLK_F_NEED_GET_DATA)
                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 bio_has_data(rq->bio);
}

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

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

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

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

static inline bool ublk_queue_can_use_recovery_reissue(
                struct ublk_queue *ubq)
{
        if ((ubq->flags & UBLK_F_USER_RECOVERY) &&
                        (ubq->flags & UBLK_F_USER_RECOVERY_REISSUE))
                return true;
        return false;
}

static inline bool ublk_queue_can_use_recovery(
                struct ublk_queue *ubq)
{
        if (ubq->flags & UBLK_F_USER_RECOVERY)
                return true;
        return false;
}

static inline bool ublk_can_use_recovery(struct ublk_device *ub)
{
        if (ub->dev_info.flags & UBLK_F_USER_RECOVERY)
                return true;
        return false;
}

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

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

static void ublk_store_owner_uid_gid(unsigned int *owner_uid,
                unsigned int *owner_gid)
{
        kuid_t uid;
        kgid_t gid;

        current_uid_gid(&uid, &gid);

        *owner_uid = from_kuid(&init_user_ns, uid);
        *owner_gid = from_kgid(&init_user_ns, gid);
}

static int ublk_open(struct block_device *bdev, fmode_t mode)
{
        struct ublk_device *ub = bdev->bd_disk->private_data;

        if (capable(CAP_SYS_ADMIN))
                return 0;

        /*
         * If it is one unprivileged device, only owner can open
         * the disk. Otherwise it could be one trap made by one
         * evil user who grants this disk's privileges to other
         * users deliberately.
         *
         * This way is reasonable too given anyone can create
         * unprivileged device, and no need other's grant.
         */
        if (ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV) {
                unsigned int curr_uid, curr_gid;

                ublk_store_owner_uid_gid(&curr_uid, &curr_gid);

                if (curr_uid != ub->dev_info.owner_uid || curr_gid !=
                                ub->dev_info.owner_gid)
                        return -EPERM;
        }

        return 0;
}

static const struct block_device_operations ub_fops = {
        .owner =        THIS_MODULE,
        .open =         ublk_open,
        .free_disk =    ublk_free_disk,
};

#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_FUA)
                flags |= UBLK_IO_F_FUA;

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

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

        return flags;
}

static blk_status_t ublk_setup_iod(struct ublk_queue *ubq, struct request *req)
{
        struct ublksrv_io_desc *iod = ublk_get_iod(ubq, req->tag);
        struct ublk_io *io = &ubq->ios[req->tag];
        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 inline 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;
        blk_status_t res = BLK_STS_OK;

        /* 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)
                goto exit;

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

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

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

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

/*
 * Since __ublk_rq_task_work always fails requests immediately during
 * exiting, __ublk_fail_req() is only called from abort context during
 * exiting. So lock is unnecessary.
 *
 * Also aborting may not be started yet, keep in mind that one failed
 * request may be issued by block layer again.
 */
static void __ublk_fail_req(struct ublk_queue *ubq, struct ublk_io *io,
                struct request *req)
{
        WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_ACTIVE);

        if (!(io->flags & UBLK_IO_FLAG_ABORTED)) {
                io->flags |= UBLK_IO_FLAG_ABORTED;
                if (ublk_queue_can_use_recovery_reissue(ubq))
                        blk_mq_requeue_request(req, false);
                else
                        blk_mq_end_request(req, BLK_STS_IOERR);
        }
}

static void ubq_complete_io_cmd(struct ublk_io *io, int res)
{
        /* mark this cmd owned by ublksrv */
        io->flags |= UBLK_IO_FLAG_OWNED_BY_SRV;

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

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

#define UBLK_REQUEUE_DELAY_MS   3

static inline void __ublk_abort_rq(struct ublk_queue *ubq,
                struct request *rq)
{
        /* We cannot process this rq so just requeue it. */
        if (ublk_queue_can_use_recovery(ubq))
                blk_mq_requeue_request(rq, false);
        else
                blk_mq_end_request(rq, BLK_STS_IOERR);

        mod_delayed_work(system_wq, &ubq->dev->monitor_work, 0);
}

static inline void __ublk_rq_task_work(struct request *req)
{
        struct ublk_queue *ubq = req->mq_hctx->driver_data;
        int tag = req->tag;
        struct ublk_io *io = &ubq->ios[tag];
        unsigned int mapped_bytes;

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

        /*
         * Task is exiting if either:
         *
         * (1) current != ubq_daemon.
         * io_uring_cmd_complete_in_task() tries to run task_work
         * in a workqueue if ubq_daemon(cmd's task) is PF_EXITING.
         *
         * (2) current->flags & PF_EXITING.
         */
        if (unlikely(current != ubq->ubq_daemon || current->flags & PF_EXITING)) {
                __ublk_abort_rq(ubq, req);
                return;
        }

        if (ublk_need_get_data(ubq) &&
                        (req_op(req) == REQ_OP_WRITE ||
                        req_op(req) == REQ_OP_FLUSH)) {
                /*
                 * We have not handled UBLK_IO_NEED_GET_DATA command yet,
                 * so immepdately pass UBLK_IO_RES_NEED_GET_DATA to ublksrv
                 * and notify it.
                 */
                if (!(io->flags & UBLK_IO_FLAG_NEED_GET_DATA)) {
                        io->flags |= UBLK_IO_FLAG_NEED_GET_DATA;
                        pr_devel("%s: need get data. op %d, qid %d tag %d io_flags %x\n",
                                        __func__, io->cmd->cmd_op, ubq->q_id,
                                        req->tag, io->flags);
                        ubq_complete_io_cmd(io, UBLK_IO_RES_NEED_GET_DATA);
                        return;
                }
                /*
                 * We have handled UBLK_IO_NEED_GET_DATA command,
                 * so clear UBLK_IO_FLAG_NEED_GET_DATA now and just
                 * do the copy work.
                 */
                io->flags &= ~UBLK_IO_FLAG_NEED_GET_DATA;
                /* update iod->addr because ublksrv may have passed a new io buffer */
                ublk_get_iod(ubq, req->tag)->addr = io->addr;
                pr_devel("%s: update iod->addr: op %d, qid %d tag %d io_flags %x addr %llx\n",
                                __func__, io->cmd->cmd_op, ubq->q_id, req->tag, io->flags,
                                ublk_get_iod(ubq, req->tag)->addr);
        }

        mapped_bytes = ublk_map_io(ubq, req, io);

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

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

        ubq_complete_io_cmd(io, UBLK_IO_RES_OK);
}

static inline void ublk_forward_io_cmds(struct ublk_queue *ubq)
{
        struct llist_node *io_cmds = llist_del_all(&ubq->io_cmds);
        struct ublk_rq_data *data, *tmp;

        io_cmds = llist_reverse_order(io_cmds);
        llist_for_each_entry_safe(data, tmp, io_cmds, node)
                __ublk_rq_task_work(blk_mq_rq_from_pdu(data));
}

static inline void ublk_abort_io_cmds(struct ublk_queue *ubq)
{
        struct llist_node *io_cmds = llist_del_all(&ubq->io_cmds);
        struct ublk_rq_data *data, *tmp;

        llist_for_each_entry_safe(data, tmp, io_cmds, node)
                __ublk_abort_rq(ubq, blk_mq_rq_from_pdu(data));
}

static void ublk_rq_task_work_cb(struct io_uring_cmd *cmd)
{
        struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
        struct ublk_queue *ubq = pdu->ubq;

        ublk_forward_io_cmds(ubq);
}

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);
        struct ublk_queue *ubq = req->mq_hctx->driver_data;

        ublk_forward_io_cmds(ubq);
}

static void ublk_queue_cmd(struct ublk_queue *ubq, struct request *rq)
{
        struct ublk_rq_data *data = blk_mq_rq_to_pdu(rq);
        struct ublk_io *io;

        if (!llist_add(&data->node, &ubq->io_cmds))
                return;

        io = &ubq->ios[rq->tag];
        /*
         * If the check pass, we know that this is a re-issued request aborted
         * previously in monitor_work because the ubq_daemon(cmd's task) is
         * PF_EXITING. We cannot call io_uring_cmd_complete_in_task() anymore
         * because this ioucmd's io_uring context may be freed now if no inflight
         * ioucmd exists. Otherwise we may cause null-deref in ctx->fallback_work.
         *
         * Note: monitor_work sets UBLK_IO_FLAG_ABORTED and ends this request(releasing
         * the tag). Then the request is re-started(allocating the tag) and we are here.
         * Since releasing/allocating a tag implies smp_mb(), finding UBLK_IO_FLAG_ABORTED
         * guarantees that here is a re-issued request aborted previously.
         */
        if (unlikely(io->flags & UBLK_IO_FLAG_ABORTED)) {
                ublk_abort_io_cmds(ubq);
        } else if (ublk_can_use_task_work(ubq)) {
                if (task_work_add(ubq->ubq_daemon, &data->work,
                                        TWA_SIGNAL_NO_IPI))
                        ublk_abort_io_cmds(ubq);
        } else {
                struct io_uring_cmd *cmd = io->cmd;
                struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);

                pdu->ubq = ubq;
                io_uring_cmd_complete_in_task(cmd, ublk_rq_task_work_cb);
        }
}

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

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

        /* With recovery feature enabled, force_abort is set in
         * ublk_stop_dev() before calling del_gendisk(). We have to
         * abort all requeued and new rqs here to let del_gendisk()
         * move on. Besides, we cannot not call io_uring_cmd_complete_in_task()
         * to avoid UAF on io_uring ctx.
         *
         * Note: force_abort is guaranteed to be seen because it is set
         * before request queue is unqiuesced.
         */
        if (ublk_queue_can_use_recovery(ubq) && unlikely(ubq->force_abort))
                return BLK_STS_IOERR;

        blk_mq_start_request(bd->rq);

        if (unlikely(ubq_daemon_is_dying(ubq))) {
                __ublk_abort_rq(ubq, rq);
                return BLK_STS_OK;
        }

        ublk_queue_cmd(ubq, rq);

        return BLK_STS_OK;
}

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

        hctx->driver_data = ubq;
        return 0;
}

static 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,
        .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 (test_and_set_bit(UB_STATE_OPEN, &ub->state))
                return -EBUSY;
        filp->private_data = ub;
        return 0;
}

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

        clear_bit(UB_STATE_OPEN, &ub->state);
        return 0;
}

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

        spin_lock(&ub->mm_lock);
        if (!ub->mm)
                ub->mm = current->mm;
        if (current->mm != ub->mm)
                ret = -EINVAL;
        spin_unlock(&ub->mm_lock);

        if (ret)
                return ret;

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

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

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

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

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

static void ublk_commit_completion(struct ublk_device *ub,
                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(ubq, io, rq);
                }
        }
        ublk_put_device(ub);
}

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

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

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

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

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

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

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

        if (!ublk_queue_ready(ubq))
                return;

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

                if (io->flags & UBLK_IO_FLAG_ACTIVE)
                        io_uring_cmd_done(io->cmd, UBLK_IO_RES_ABORT, 0);
        }

        /* all io commands are canceled */
        ubq->nr_io_ready = 0;
}

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

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

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

        if (blk_mq_request_started(rq)) {
                *idle = false;
                return false;
        }
        return true;
}

static void ublk_wait_tagset_rqs_idle(struct ublk_device *ub)
{
        bool idle;

        WARN_ON_ONCE(!blk_queue_quiesced(ub->ub_disk->queue));
        while (true) {
                idle = true;
                blk_mq_tagset_busy_iter(&ub->tag_set,
                                ublk_check_inflight_rq, &idle);
                if (idle)
                        break;
                msleep(UBLK_REQUEUE_DELAY_MS);
        }
}

static void __ublk_quiesce_dev(struct ublk_device *ub)
{
        pr_devel("%s: quiesce ub: dev_id %d state %s\n",
                        __func__, ub->dev_info.dev_id,
                        ub->dev_info.state == UBLK_S_DEV_LIVE ?
                        "LIVE" : "QUIESCED");
        blk_mq_quiesce_queue(ub->ub_disk->queue);
        ublk_wait_tagset_rqs_idle(ub);
        ub->dev_info.state = UBLK_S_DEV_QUIESCED;
        ublk_cancel_dev(ub);
        /* we are going to release task_struct of ubq_daemon and resets
         * ->ubq_daemon to NULL. So in monitor_work, check on ubq_daemon causes UAF.
         * Besides, monitor_work is not necessary in QUIESCED state since we have
         * already scheduled quiesce_work and quiesced all ubqs.
         *
         * Do not let monitor_work schedule itself if state it QUIESCED. And we cancel
         * it here and re-schedule it in END_USER_RECOVERY to avoid UAF.
         */
        cancel_delayed_work_sync(&ub->monitor_work);
}

static void ublk_quiesce_work_fn(struct work_struct *work)
{
        struct ublk_device *ub =
                container_of(work, struct ublk_device, quiesce_work);

        mutex_lock(&ub->mutex);
        if (ub->dev_info.state != UBLK_S_DEV_LIVE)
                goto unlock;
        __ublk_quiesce_dev(ub);
 unlock:
        mutex_unlock(&ub->mutex);
}

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

        pr_devel("%s: unquiesce ub: dev_id %d state %s\n",
                        __func__, ub->dev_info.dev_id,
                        ub->dev_info.state == UBLK_S_DEV_LIVE ?
                        "LIVE" : "QUIESCED");
        /* quiesce_work has run. We let requeued rqs be aborted
         * before running fallback_wq. "force_abort" must be seen
         * after request queue is unqiuesced. Then del_gendisk()
         * can move on.
         */
        for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
                ublk_get_queue(ub, i)->force_abort = true;

        blk_mq_unquiesce_queue(ub->ub_disk->queue);
        /* We may have requeued some rqs in ublk_quiesce_queue() */
        blk_mq_kick_requeue_list(ub->ub_disk->queue);
}

static void ublk_stop_dev(struct ublk_device *ub)
{
        mutex_lock(&ub->mutex);
        if (ub->dev_info.state == UBLK_S_DEV_DEAD)
                goto unlock;
        if (ublk_can_use_recovery(ub)) {
                if (ub->dev_info.state == UBLK_S_DEV_LIVE)
                        __ublk_quiesce_dev(ub);
                ublk_unquiesce_dev(ub);
        }
        del_gendisk(ub->ub_disk);
        ub->dev_info.state = UBLK_S_DEV_DEAD;
        ub->dev_info.ublksrv_pid = -1;
        put_disk(ub->ub_disk);
        ub->ub_disk = NULL;
 unlock:
        ublk_cancel_dev(ub);
        mutex_unlock(&ub->mutex);
        cancel_delayed_work_sync(&ub->monitor_work);
}

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

                if (capable(CAP_SYS_ADMIN))
                        ub->nr_privileged_daemon++;
        }
        if (ub->nr_queues_ready == ub->dev_info.nr_hw_queues)
                complete_all(&ub->completion);
        mutex_unlock(&ub->mutex);
}

static void ublk_handle_need_get_data(struct ublk_device *ub, int q_id,
                int tag)
{
        struct ublk_queue *ubq = ublk_get_queue(ub, q_id);
        struct request *req = blk_mq_tag_to_rq(ub->tag_set.tags[q_id], tag);

        ublk_queue_cmd(ubq, req);
}

static 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;
        struct request *req;

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

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

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

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

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

        io = &ubq->ios[tag];

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

        /*
         * ensure that the user issues UBLK_IO_NEED_GET_DATA
         * iff the driver have set the UBLK_IO_FLAG_NEED_GET_DATA.
         */
        if ((!!(io->flags & UBLK_IO_FLAG_NEED_GET_DATA))
                        ^ (cmd_op == UBLK_IO_NEED_GET_DATA))
                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 NEED GET DATA is not enabled */
                if (!ub_cmd->addr && !ublk_need_get_data(ubq))
                        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:
                req = blk_mq_tag_to_rq(ub->tag_set.tags[ub_cmd->q_id], tag);
                /*
                 * COMMIT_AND_FETCH_REQ has to provide IO buffer if NEED GET DATA is
                 * not enabled or it is Read IO.
                 */
                if (!ub_cmd->addr && (!ublk_need_get_data(ubq) || req_op(req) == REQ_OP_READ))
                        goto out;
                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;
        case UBLK_IO_NEED_GET_DATA:
                if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
                        goto out;
                io->addr = ub_cmd->addr;
                io->cmd = cmd;
                io->flags |= UBLK_IO_FLAG_ACTIVE;
                ublk_handle_need_get_data(ub, ub_cmd->q_id, ub_cmd->tag);
                break;
        default:
                goto out;
        }
        return -EIOCBQUEUED;

 out:
        io_uring_cmd_done(cmd, ret, 0);
        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;
        ubq->q_id = q_id;
        ubq->q_depth = ub->dev_info.queue_depth;
        size = ublk_queue_cmd_buf_size(ub, q_id);

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

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

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

        if (!ub->__queues)
                return;

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

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

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

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

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

 fail:
        ublk_deinit_queues(ub);
        return ret;
}

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

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

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

        return err;
}

static void ublk_free_dev_number(struct ublk_device *ub)
{
        spin_lock(&ublk_idr_lock);
        idr_remove(&ublk_index_idr, ub->ub_number);
        wake_up_all(&ublk_idr_wq);
        spin_unlock(&ublk_idr_lock);
}

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

        blk_mq_free_tag_set(&ub->tag_set);
        ublk_deinit_queues(ub);
        ublk_free_dev_number(ub);
        mutex_destroy(&ub->mutex);
        kfree(ub);
}

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

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

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

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

        ublks_added++;
        return 0;
 fail:
        put_device(dev);
        return ret;
}

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

        ublk_stop_dev(ub);
}

/* align max io buffer size with PAGE_SIZE */
static void ublk_align_max_io_size(struct ublk_device *ub)
{
        unsigned int max_io_bytes = ub->dev_info.max_io_buf_bytes;

        ub->dev_info.max_io_buf_bytes =
                round_down(max_io_bytes, PAGE_SIZE);
}

static int ublk_add_tag_set(struct ublk_device *ub)
{
        ub->tag_set.ops = &ublk_mq_ops;
        ub->tag_set.nr_hw_queues = ub->dev_info.nr_hw_queues;
        ub->tag_set.queue_depth = ub->dev_info.queue_depth;
        ub->tag_set.numa_node = NUMA_NO_NODE;
        ub->tag_set.cmd_size = sizeof(struct ublk_rq_data);
        ub->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
        ub->tag_set.driver_data = ub;
        return blk_mq_alloc_tag_set(&ub->tag_set);
}

static void ublk_remove(struct ublk_device *ub)
{
        ublk_stop_dev(ub);
        cancel_work_sync(&ub->stop_work);
        cancel_work_sync(&ub->quiesce_work);
        cdev_device_del(&ub->cdev, &ub->cdev_dev);
        put_device(&ub->cdev_dev);
        ublks_added--;
}

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

        if (idx < 0)
                return NULL;

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

        return ub;
}

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

        if (ublksrv_pid <= 0)
                return -EINVAL;

        wait_for_completion_interruptible(&ub->completion);

        schedule_delayed_work(&ub->monitor_work, UBLK_DAEMON_MONITOR_PERIOD);

        mutex_lock(&ub->mutex);
        if (ub->dev_info.state == UBLK_S_DEV_LIVE ||
            test_bit(UB_STATE_USED, &ub->state)) {
                ret = -EEXIST;
                goto out_unlock;
        }

        disk = blk_mq_alloc_disk(&ub->tag_set, NULL);
        if (IS_ERR(disk)) {
                ret = PTR_ERR(disk);
                goto out_unlock;
        }
        sprintf(disk->disk_name, "ublkb%d", ub->ub_number);
        disk->fops = &ub_fops;
        disk->private_data = ub;

        ub->dev_info.ublksrv_pid = ublksrv_pid;
        ub->ub_disk = disk;

        ret = ublk_apply_params(ub);
        if (ret)
                goto out_put_disk;

        /* don't probe partitions if any one ubq daemon is un-trusted */
        if (ub->nr_privileged_daemon != ub->nr_queues_ready)
                set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);

        get_device(&ub->cdev_dev);
        ret = add_disk(disk);
        if (ret) {
                /*
                 * Has to drop the reference since ->free_disk won't be
                 * called in case of add_disk failure.
                 */
                ublk_put_device(ub);
                goto out_put_disk;
        }
        set_bit(UB_STATE_USED, &ub->state);
        ub->dev_info.state = UBLK_S_DEV_LIVE;
out_put_disk:
        if (ret)
                put_disk(disk);
out_unlock:
        mutex_unlock(&ub->mutex);
        return ret;
}

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

        if (header->len * BITS_PER_BYTE < nr_cpu_ids)
                return -EINVAL;
        if (header->len & (sizeof(unsigned long)-1))
                return -EINVAL;
        if (!header->addr)
                return -EINVAL;

        queue = header->data[0];
        if (queue >= ub->dev_info.nr_hw_queues)
                return -EINVAL;

        if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
                return -ENOMEM;

        for_each_possible_cpu(i) {
                if (ub->tag_set.map[HCTX_TYPE_DEFAULT].mq_map[i] == queue)
                        cpumask_set_cpu(i, cpumask);
        }

        ret = -EFAULT;
        retlen = min_t(unsigned short, header->len, cpumask_size());
        if (copy_to_user(argp, cpumask, retlen))
                goto out_free_cpumask;
        if (retlen != header->len &&
            clear_user(argp + retlen, header->len - retlen))
                goto out_free_cpumask;

        ret = 0;
out_free_cpumask:
        free_cpumask_var(cpumask);
        return ret;
}

static inline void ublk_dump_dev_info(struct ublksrv_ctrl_dev_info *info)
{
        pr_devel("%s: dev id %d flags %llx\n", __func__,
                        info->dev_id, info->flags);
        pr_devel("\t nr_hw_queues %d queue_depth %d\n",
                        info->nr_hw_queues, info->queue_depth);
}

static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd)
{
        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;
        struct ublk_device *ub;
        int ret = -EINVAL;

        if (header->len < sizeof(info) || !header->addr)
                return -EINVAL;
        if (header->queue_id != (u16)-1) {
                pr_warn("%s: queue_id is wrong %x\n",
                        __func__, header->queue_id);
                return -EINVAL;
        }

        if (copy_from_user(&info, argp, sizeof(info)))
                return -EFAULT;

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

        /* the created device is always owned by current user */
        ublk_store_owner_uid_gid(&info.owner_uid, &info.owner_gid);

        if (header->dev_id != info.dev_id) {
                pr_warn("%s: dev id not match %u %u\n",
                        __func__, header->dev_id, info.dev_id);
                return -EINVAL;
        }

        ublk_dump_dev_info(&info);

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

        ret = -EACCES;
        if (ublks_added >= ublks_max)
                goto out_unlock;

        ret = -ENOMEM;
        ub = kzalloc(sizeof(*ub), GFP_KERNEL);
        if (!ub)
                goto out_unlock;
        mutex_init(&ub->mutex);
        spin_lock_init(&ub->mm_lock);
        INIT_WORK(&ub->quiesce_work, ublk_quiesce_work_fn);
        INIT_WORK(&ub->stop_work, ublk_stop_work_fn);
        INIT_DELAYED_WORK(&ub->monitor_work, ublk_daemon_monitor_work);

        ret = ublk_alloc_dev_number(ub, header->dev_id);
        if (ret < 0)
                goto out_free_ub;

        memcpy(&ub->dev_info, &info, sizeof(info));

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

        /*
         * 64bit flags will be copied back to userspace as feature
         * negotiation result, so have to clear flags which driver
         * doesn't support yet, then userspace can get correct flags
         * (features) to handle.
         */
        ub->dev_info.flags &= UBLK_F_ALL;

        if (!IS_BUILTIN(CONFIG_BLK_DEV_UBLK))
                ub->dev_info.flags |= UBLK_F_URING_CMD_COMP_IN_TASK;

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

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

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

        ret = ublk_add_tag_set(ub);
        if (ret)
                goto out_deinit_queues;

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

        /*
         * Add the char dev so that ublksrv daemon can be setup.
         * ublk_add_chdev() will cleanup everything if it fails.
         */
        ret = ublk_add_chdev(ub);
        goto out_unlock;

out_free_tag_set:
        blk_mq_free_tag_set(&ub->tag_set);
out_deinit_queues:
        ublk_deinit_queues(ub);
out_free_dev_number:
        ublk_free_dev_number(ub);
out_free_ub:
        mutex_destroy(&ub->mutex);
        kfree(ub);
out_unlock:
        mutex_unlock(&ublk_ctl_mutex);
        return ret;
}

static inline bool ublk_idr_freed(int id)
{
        void *ptr;

        spin_lock(&ublk_idr_lock);
        ptr = idr_find(&ublk_index_idr, id);
        spin_unlock(&ublk_idr_lock);

        return ptr == NULL;
}

static int ublk_ctrl_del_dev(struct ublk_device **p_ub)
{
        struct ublk_device *ub = *p_ub;
        int idx = ub->ub_number;
        int ret;

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

        if (!test_bit(UB_STATE_DELETED, &ub->state)) {
                ublk_remove(ub);
                set_bit(UB_STATE_DELETED, &ub->state);
        }

        /* Mark the reference as consumed */
        *p_ub = NULL;
        ublk_put_device(ub);
        mutex_unlock(&ublk_ctl_mutex);

        /*
         * Wait until the idr is removed, then it can be reused after
         * DEL_DEV command is returned.
         *
         * If we returns because of user interrupt, future delete command
         * may come:
         *
         * - the device number isn't freed, this device won't or needn't
         *   be deleted again, since UB_STATE_DELETED is set, and device
         *   will be released after the last reference is dropped
         *
         * - the device number is freed already, we will not find this
         *   device via ublk_get_device_from_id()
         */
        wait_event_interruptible(ublk_idr_wq, ublk_idr_freed(idx));

        return 0;
}

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_stop_dev(struct ublk_device *ub)
{
        ublk_stop_dev(ub);
        cancel_work_sync(&ub->stop_work);
        cancel_work_sync(&ub->quiesce_work);

        return 0;
}

static int ublk_ctrl_get_dev_info(struct ublk_device *ub,
                struct io_uring_cmd *cmd)
{
        struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
        void __user *argp = (void __user *)(unsigned long)header->addr;

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

        if (copy_to_user(argp, &ub->dev_info, sizeof(ub->dev_info)))
                return -EFAULT;

        return 0;
}

/* TYPE_DEVT is readonly, so fill it up before returning to userspace */
static void ublk_ctrl_fill_params_devt(struct ublk_device *ub)
{
        ub->params.devt.char_major = MAJOR(ub->cdev_dev.devt);
        ub->params.devt.char_minor = MINOR(ub->cdev_dev.devt);

        if (ub->ub_disk) {
                ub->params.devt.disk_major = MAJOR(disk_devt(ub->ub_disk));
                ub->params.devt.disk_minor = MINOR(disk_devt(ub->ub_disk));
        } else {
                ub->params.devt.disk_major = 0;
                ub->params.devt.disk_minor = 0;
        }
        ub->params.types |= UBLK_PARAM_TYPE_DEVT;
}

static int ublk_ctrl_get_params(struct ublk_device *ub,
                struct io_uring_cmd *cmd)
{
        struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
        void __user *argp = (void __user *)(unsigned long)header->addr;
        struct ublk_params_header ph;
        int ret;

        if (header->len <= sizeof(ph) || !header->addr)
                return -EINVAL;

        if (copy_from_user(&ph, argp, sizeof(ph)))
                return -EFAULT;

        if (ph.len > header->len || !ph.len)
                return -EINVAL;

        if (ph.len > sizeof(struct ublk_params))
                ph.len = sizeof(struct ublk_params);

        mutex_lock(&ub->mutex);
        ublk_ctrl_fill_params_devt(ub);
        if (copy_to_user(argp, &ub->params, ph.len))
                ret = -EFAULT;
        else
                ret = 0;
        mutex_unlock(&ub->mutex);

        return ret;
}

static int ublk_ctrl_set_params(struct ublk_device *ub,
                struct io_uring_cmd *cmd)
{
        struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
        void __user *argp = (void __user *)(unsigned long)header->addr;
        struct ublk_params_header ph;
        int ret = -EFAULT;

        if (header->len <= sizeof(ph) || !header->addr)
                return -EINVAL;

        if (copy_from_user(&ph, argp, sizeof(ph)))
                return -EFAULT;

        if (ph.len > header->len || !ph.len || !ph.types)
                return -EINVAL;

        if (ph.len > sizeof(struct ublk_params))
                ph.len = sizeof(struct ublk_params);

        /* parameters can only be changed when device isn't live */
        mutex_lock(&ub->mutex);
        if (ub->dev_info.state == UBLK_S_DEV_LIVE) {
                ret = -EACCES;
        } else if (copy_from_user(&ub->params, argp, ph.len)) {
                ret = -EFAULT;
        } else {
                /* clear all we don't support yet */
                ub->params.types &= UBLK_PARAM_TYPE_ALL;
                ret = ublk_validate_params(ub);
        }
        mutex_unlock(&ub->mutex);

        return ret;
}

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

        WARN_ON_ONCE(!(ubq->ubq_daemon && ubq_daemon_is_dying(ubq)));
        /* All old ioucmds have to be completed */
        WARN_ON_ONCE(ubq->nr_io_ready);
        /* old daemon is PF_EXITING, put it now */
        put_task_struct(ubq->ubq_daemon);
        /* We have to reset it to NULL, otherwise ub won't accept new FETCH_REQ */
        ubq->ubq_daemon = NULL;

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

                /* forget everything now and be ready for new FETCH_REQ */
                io->flags = 0;
                io->cmd = NULL;
                io->addr = 0;
        }
}

static int ublk_ctrl_start_recovery(struct ublk_device *ub,
                struct io_uring_cmd *cmd)
{
        struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
        int ret = -EINVAL;
        int i;

        mutex_lock(&ub->mutex);
        if (!ublk_can_use_recovery(ub))
                goto out_unlock;
        /*
         * START_RECOVERY is only allowd after:
         *
         * (1) UB_STATE_OPEN is not set, which means the dying process is exited
         *     and related io_uring ctx is freed so file struct of /dev/ublkcX is
         *     released.
         *
         * (2) UBLK_S_DEV_QUIESCED is set, which means the quiesce_work:
         *     (a)has quiesced request queue
         *     (b)has requeued every inflight rqs whose io_flags is ACTIVE
         *     (c)has requeued/aborted every inflight rqs whose io_flags is NOT ACTIVE
         *     (d)has completed/camceled all ioucmds owned by ther dying process
         */
        if (test_bit(UB_STATE_OPEN, &ub->state) ||
                        ub->dev_info.state != UBLK_S_DEV_QUIESCED) {
                ret = -EBUSY;
                goto out_unlock;
        }
        pr_devel("%s: start recovery for dev id %d.\n", __func__, header->dev_id);
        for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
                ublk_queue_reinit(ub, ublk_get_queue(ub, i));
        /* set to NULL, otherwise new ubq_daemon cannot mmap the io_cmd_buf */
        ub->mm = NULL;
        ub->nr_queues_ready = 0;
        ub->nr_privileged_daemon = 0;
        init_completion(&ub->completion);
        ret = 0;
 out_unlock:
        mutex_unlock(&ub->mutex);
        return ret;
}

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

        pr_devel("%s: Waiting for new ubq_daemons(nr: %d) are ready, dev id %d...\n",
                        __func__, ub->dev_info.nr_hw_queues, header->dev_id);
        /* wait until new ubq_daemon sending all FETCH_REQ */
        wait_for_completion_interruptible(&ub->completion);
        pr_devel("%s: All new ubq_daemons(nr: %d) are ready, dev id %d\n",
                        __func__, ub->dev_info.nr_hw_queues, header->dev_id);

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

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

/*
 * All control commands are sent via /dev/ublk-control, so we have to check
 * the destination device's permission
 */
static int ublk_char_dev_permission(struct ublk_device *ub,
                const char *dev_path, int mask)
{
        int err;
        struct path path;
        struct kstat stat;

        err = kern_path(dev_path, LOOKUP_FOLLOW, &path);
        if (err)
                return err;

        err = vfs_getattr(&path, &stat, STATX_TYPE, AT_STATX_SYNC_AS_STAT);
        if (err)
                goto exit;

        err = -EPERM;
        if (stat.rdev != ub->cdev_dev.devt || !S_ISCHR(stat.mode))
                goto exit;

        err = inode_permission(&nop_mnt_idmap,
                        d_backing_inode(path.dentry), mask);
exit:
        path_put(&path);
        return err;
}

static int ublk_ctrl_uring_cmd_permission(struct ublk_device *ub,
                struct io_uring_cmd *cmd)
{
        struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
        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 (cmd->cmd_op != UBLK_CMD_GET_DEV_INFO2)
                        return 0;
        }

        /*
         * User has to provide the char device path for unprivileged ublk
         *
         * header->addr always points to the dev path buffer, and
         * header->dev_path_len records length of dev path buffer.
         */
        if (!header->dev_path_len || header->dev_path_len > PATH_MAX)
                return -EINVAL;

        if (header->len < header->dev_path_len)
                return -EINVAL;

        dev_path = kmalloc(header->dev_path_len + 1, GFP_KERNEL);
        if (!dev_path)
                return -ENOMEM;

        ret = -EFAULT;
        if (copy_from_user(dev_path, argp, header->dev_path_len))
                goto exit;
        dev_path[header->dev_path_len] = 0;

        ret = -EINVAL;
        switch (cmd->cmd_op) {
        case UBLK_CMD_GET_DEV_INFO:
        case UBLK_CMD_GET_DEV_INFO2:
        case UBLK_CMD_GET_QUEUE_AFFINITY:
        case UBLK_CMD_GET_PARAMS:
                mask = MAY_READ;
                break;
        case UBLK_CMD_START_DEV:
        case UBLK_CMD_STOP_DEV:
        case UBLK_CMD_ADD_DEV:
        case UBLK_CMD_DEL_DEV:
        case UBLK_CMD_SET_PARAMS:
        case UBLK_CMD_START_USER_RECOVERY:
        case UBLK_CMD_END_USER_RECOVERY:
                mask = MAY_READ | MAY_WRITE;
                break;
        default:
                goto exit;
        }

        ret = ublk_char_dev_permission(ub, dev_path, mask);
        if (!ret) {
                header->len -= header->dev_path_len;
                header->addr += header->dev_path_len;
        }
        pr_devel("%s: dev id %d cmd_op %x uid %d gid %d path %s ret %d\n",
                        __func__, ub->ub_number, cmd->cmd_op,
                        ub->dev_info.owner_uid, ub->dev_info.owner_gid,
                        dev_path, ret);
exit:
        kfree(dev_path);
        return ret;
}

static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
                unsigned int issue_flags)
{
        struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
        struct ublk_device *ub = NULL;
        int ret = -EINVAL;

        if (issue_flags & IO_URING_F_NONBLOCK)
                return -EAGAIN;

        ublk_ctrl_cmd_dump(cmd);

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

        if (cmd->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);
        } else {
                /* ADD_DEV permission check is done in command handler */
                ret = 0;
        }

        if (ret)
                goto put_dev;

        switch (cmd->cmd_op) {
        case UBLK_CMD_START_DEV:
                ret = ublk_ctrl_start_dev(ub, cmd);
                break;
        case UBLK_CMD_STOP_DEV:
                ret = ublk_ctrl_stop_dev(ub);
                break;
        case UBLK_CMD_GET_DEV_INFO:
        case UBLK_CMD_GET_DEV_INFO2:
                ret = ublk_ctrl_get_dev_info(ub, cmd);
                break;
        case UBLK_CMD_ADD_DEV:
                ret = ublk_ctrl_add_dev(cmd);
                break;
        case UBLK_CMD_DEL_DEV:
                ret = ublk_ctrl_del_dev(&ub);
                break;
        case UBLK_CMD_GET_QUEUE_AFFINITY:
                ret = ublk_ctrl_get_queue_affinity(ub, cmd);
                break;
        case UBLK_CMD_GET_PARAMS:
                ret = ublk_ctrl_get_params(ub, cmd);
                break;
        case UBLK_CMD_SET_PARAMS:
                ret = ublk_ctrl_set_params(ub, cmd);
                break;
        case UBLK_CMD_START_USER_RECOVERY:
                ret = ublk_ctrl_start_recovery(ub, cmd);
                break;
        case UBLK_CMD_END_USER_RECOVERY:
                ret = ublk_ctrl_end_recovery(ub, cmd);
                break;
        default:
                ret = -ENOTSUPP;
                break;
        }

 put_dev:
        if (ub)
                ublk_put_device(ub);
 out:
        io_uring_cmd_done(cmd, ret, 0);
        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;

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

        class_destroy(ublk_chr_class);
        misc_deregister(&ublk_misc);

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

module_init(ublk_init);
module_exit(ublk_exit);

module_param(ublks_max, int, 0444);
MODULE_PARM_DESC(ublks_max, "max number of ublk devices allowed to add(default: 64)");

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