xref: /linux/drivers/block/loop.c (revision 6a069876eb1402478900ee0eb7d7fe276bb1f4e3)

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright 1993 by Theodore Ts'o.
 */
#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/blkpg.h>
#include <linux/init.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/compat.h>
#include <linux/suspend.h>
#include <linux/freezer.h>
#include <linux/mutex.h>
#include <linux/writeback.h>
#include <linux/completion.h>
#include <linux/highmem.h>
#include <linux/splice.h>
#include <linux/sysfs.h>
#include <linux/miscdevice.h>
#include <linux/falloc.h>
#include <linux/uio.h>
#include <linux/ioprio.h>
#include <linux/blk-cgroup.h>
#include <linux/sched/mm.h>
#include <linux/statfs.h>
#include <linux/uaccess.h>
#include <linux/blk-mq.h>
#include <linux/spinlock.h>
#include <uapi/linux/loop.h>

/* Possible states of device */
enum {
	Lo_unbound,
	Lo_bound,
	Lo_rundown,
	Lo_deleting,
};

struct loop_device {
	int		lo_number;
	loff_t		lo_offset;
	loff_t		lo_sizelimit;
	int		lo_flags;
	char		lo_file_name[LO_NAME_SIZE];

	struct file	*lo_backing_file;
	unsigned int	lo_min_dio_size;
	struct block_device *lo_device;

	gfp_t		old_gfp_mask;

	spinlock_t		lo_lock;
	int			lo_state;
	spinlock_t              lo_work_lock;
	struct workqueue_struct *workqueue;
	struct work_struct      rootcg_work;
	struct list_head        rootcg_cmd_list;
	struct list_head        idle_worker_list;
	struct rb_root          worker_tree;
	struct timer_list       timer;
	bool			sysfs_inited;

	struct request_queue	*lo_queue;
	struct blk_mq_tag_set	tag_set;
	struct gendisk		*lo_disk;
	struct mutex		lo_mutex;
	bool			idr_visible;
};

struct loop_cmd {
	struct list_head list_entry;
	bool use_aio; /* use AIO interface to handle I/O */
	atomic_t ref; /* only for aio */
	long ret;
	struct kiocb iocb;
	struct bio_vec *bvec;
	struct cgroup_subsys_state *blkcg_css;
	struct cgroup_subsys_state *memcg_css;
};

#define LOOP_IDLE_WORKER_TIMEOUT (60 * HZ)
#define LOOP_DEFAULT_HW_Q_DEPTH 128

static DEFINE_IDR(loop_index_idr);
static DEFINE_MUTEX(loop_ctl_mutex);
static DEFINE_MUTEX(loop_validate_mutex);

/**
 * loop_global_lock_killable() - take locks for safe loop_validate_file() test
 *
 * @lo: struct loop_device
 * @global: true if @lo is about to bind another "struct loop_device", false otherwise
 *
 * Returns 0 on success, -EINTR otherwise.
 *
 * Since loop_validate_file() traverses on other "struct loop_device" if
 * is_loop_device() is true, we need a global lock for serializing concurrent
 * loop_configure()/loop_change_fd()/__loop_clr_fd() calls.
 */
static int loop_global_lock_killable(struct loop_device *lo, bool global)
{
	int err;

	if (global) {
		err = mutex_lock_killable(&loop_validate_mutex);
		if (err)
			return err;
	}
	err = mutex_lock_killable(&lo->lo_mutex);
	if (err && global)
		mutex_unlock(&loop_validate_mutex);
	return err;
}

/**
 * loop_global_unlock() - release locks taken by loop_global_lock_killable()
 *
 * @lo: struct loop_device
 * @global: true if @lo was about to bind another "struct loop_device", false otherwise
 */
static void loop_global_unlock(struct loop_device *lo, bool global)
{
	mutex_unlock(&lo->lo_mutex);
	if (global)
		mutex_unlock(&loop_validate_mutex);
}

static int max_part;
static int part_shift;

static loff_t lo_calculate_size(struct loop_device *lo, struct file *file)
{
	loff_t loopsize;
	int ret;

	if (S_ISBLK(file_inode(file)->i_mode)) {
		loopsize = i_size_read(file->f_mapping->host);
	} else {
		struct kstat stat;

		/*
		 * Get the accurate file size. This provides better results than
		 * cached inode data, particularly for network filesystems where
		 * metadata may be stale.
		 */
		ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);
		if (ret)
			return 0;

		loopsize = stat.size;
	}

	if (lo->lo_offset > 0)
		loopsize -= lo->lo_offset;
	/* offset is beyond i_size, weird but possible */
	if (loopsize < 0)
		return 0;
	if (lo->lo_sizelimit > 0 && lo->lo_sizelimit < loopsize)
		loopsize = lo->lo_sizelimit;
	/*
	 * Unfortunately, if we want to do I/O on the device,
	 * the number of 512-byte sectors has to fit into a sector_t.
	 */
	return loopsize >> 9;
}

/*
 * We support direct I/O only if lo_offset is aligned with the logical I/O size
 * of backing device, and the logical block size of loop is bigger than that of
 * the backing device.
 */
static bool lo_can_use_dio(struct loop_device *lo)
{
	if (!(lo->lo_backing_file->f_mode & FMODE_CAN_ODIRECT))
		return false;
	if (queue_logical_block_size(lo->lo_queue) < lo->lo_min_dio_size)
		return false;
	if (lo->lo_offset & (lo->lo_min_dio_size - 1))
		return false;
	return true;
}

/*
 * Direct I/O can be enabled either by using an O_DIRECT file descriptor, or by
 * passing in the LO_FLAGS_DIRECT_IO flag from userspace.  It will be silently
 * disabled when the device block size is too small or the offset is unaligned.
 *
 * loop_get_status will always report the effective LO_FLAGS_DIRECT_IO flag and
 * not the originally passed in one.
 */
static inline void loop_update_dio(struct loop_device *lo)
{
	lockdep_assert_held(&lo->lo_mutex);
	WARN_ON_ONCE(lo->lo_state == Lo_bound &&
		     lo->lo_queue->mq_freeze_depth == 0);

	if ((lo->lo_flags & LO_FLAGS_DIRECT_IO) && !lo_can_use_dio(lo))
		lo->lo_flags &= ~LO_FLAGS_DIRECT_IO;
}

/**
 * loop_set_size() - sets device size and notifies userspace
 * @lo: struct loop_device to set the size for
 * @size: new size of the loop device
 *
 * Callers must validate that the size passed into this function fits into
 * a sector_t, eg using loop_validate_size()
 */
static void loop_set_size(struct loop_device *lo, loff_t size)
{
	if (!set_capacity_and_notify(lo->lo_disk, size))
		kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);
}

static void loop_clear_limits(struct loop_device *lo, int mode)
{
	struct queue_limits lim = queue_limits_start_update(lo->lo_queue);

	if (mode & FALLOC_FL_ZERO_RANGE)
		lim.max_write_zeroes_sectors = 0;

	if (mode & FALLOC_FL_PUNCH_HOLE) {
		lim.max_hw_discard_sectors = 0;
		lim.discard_granularity = 0;
	}

	/*
	 * XXX: this updates the queue limits without freezing the queue, which
	 * is against the locking protocol and dangerous.  But we can't just
	 * freeze the queue as we're inside the ->queue_rq method here.  So this
	 * should move out into a workqueue unless we get the file operations to
	 * advertise if they support specific fallocate operations.
	 */
	queue_limits_commit_update(lo->lo_queue, &lim);
}

static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
			int mode)
{
	/*
	 * We use fallocate to manipulate the space mappings used by the image
	 * a.k.a. discard/zerorange.
	 */
	struct file *file = lo->lo_backing_file;
	int ret;

	mode |= FALLOC_FL_KEEP_SIZE;

	if (!bdev_max_discard_sectors(lo->lo_device))
		return -EOPNOTSUPP;

	ret = file->f_op->fallocate(file, mode, pos, blk_rq_bytes(rq));
	if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
		return -EIO;

	/*
	 * We initially configure the limits in a hope that fallocate is
	 * supported and clear them here if that turns out not to be true.
	 */
	if (unlikely(ret == -EOPNOTSUPP))
		loop_clear_limits(lo, mode);

	return ret;
}

static int lo_req_flush(struct loop_device *lo, struct request *rq)
{
	int ret = vfs_fsync(lo->lo_backing_file, 0);
	if (unlikely(ret && ret != -EINVAL))
		ret = -EIO;

	return ret;
}

static void lo_complete_rq(struct request *rq)
{
	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
	blk_status_t ret = BLK_STS_OK;

	if (cmd->ret < 0 || cmd->ret == blk_rq_bytes(rq) ||
	    req_op(rq) != REQ_OP_READ) {
		if (cmd->ret < 0)
			ret = errno_to_blk_status(cmd->ret);
		goto end_io;
	}

	/*
	 * Short READ - if we got some data, advance our request and
	 * retry it. If we got no data, end the rest with EIO.
	 */
	if (cmd->ret) {
		blk_update_request(rq, BLK_STS_OK, cmd->ret);
		cmd->ret = 0;
		blk_mq_requeue_request(rq, true);
	} else {
		struct bio *bio = rq->bio;

		while (bio) {
			zero_fill_bio(bio);
			bio = bio->bi_next;
		}

		ret = BLK_STS_IOERR;
end_io:
		blk_mq_end_request(rq, ret);
	}
}

static void lo_rw_aio_do_completion(struct loop_cmd *cmd)
{
	struct request *rq = blk_mq_rq_from_pdu(cmd);

	if (!atomic_dec_and_test(&cmd->ref))
		return;
	kfree(cmd->bvec);
	cmd->bvec = NULL;
	if (req_op(rq) == REQ_OP_WRITE)
		kiocb_end_write(&cmd->iocb);
	if (likely(!blk_should_fake_timeout(rq->q)))
		blk_mq_complete_request(rq);
}

static void lo_rw_aio_complete(struct kiocb *iocb, long ret)
{
	struct loop_cmd *cmd = container_of(iocb, struct loop_cmd, iocb);

	cmd->ret = ret;
	lo_rw_aio_do_completion(cmd);
}

static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
		     loff_t pos, int rw)
{
	struct iov_iter iter;
	struct req_iterator rq_iter;
	struct bio_vec *bvec;
	struct request *rq = blk_mq_rq_from_pdu(cmd);
	struct bio *bio = rq->bio;
	struct file *file = lo->lo_backing_file;
	struct bio_vec tmp;
	unsigned int offset;
	unsigned int nr_bvec;
	int ret;

	nr_bvec = blk_rq_nr_bvec(rq);

	if (rq->bio != rq->biotail) {

		bvec = kmalloc_array(nr_bvec, sizeof(struct bio_vec),
				     GFP_NOIO);
		if (!bvec)
			return -EIO;
		cmd->bvec = bvec;

		/*
		 * The bios of the request may be started from the middle of
		 * the 'bvec' because of bio splitting, so we can't directly
		 * copy bio->bi_iov_vec to new bvec. The rq_for_each_bvec
		 * API will take care of all details for us.
		 */
		rq_for_each_bvec(tmp, rq, rq_iter) {
			*bvec = tmp;
			bvec++;
		}
		bvec = cmd->bvec;
		offset = 0;
	} else {
		/*
		 * Same here, this bio may be started from the middle of the
		 * 'bvec' because of bio splitting, so offset from the bvec
		 * must be passed to iov iterator
		 */
		offset = bio->bi_iter.bi_bvec_done;
		bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
	}
	atomic_set(&cmd->ref, 2);

	iov_iter_bvec(&iter, rw, bvec, nr_bvec, blk_rq_bytes(rq));
	iter.iov_offset = offset;

	cmd->iocb.ki_pos = pos;
	cmd->iocb.ki_filp = file;
	cmd->iocb.ki_ioprio = req_get_ioprio(rq);
	if (cmd->use_aio) {
		cmd->iocb.ki_complete = lo_rw_aio_complete;
		cmd->iocb.ki_flags = IOCB_DIRECT;
	} else {
		cmd->iocb.ki_complete = NULL;
		cmd->iocb.ki_flags = 0;
	}

	if (rw == ITER_SOURCE) {
		kiocb_start_write(&cmd->iocb);
		ret = file->f_op->write_iter(&cmd->iocb, &iter);
	} else
		ret = file->f_op->read_iter(&cmd->iocb, &iter);

	lo_rw_aio_do_completion(cmd);

	if (ret != -EIOCBQUEUED)
		lo_rw_aio_complete(&cmd->iocb, ret);
	return -EIOCBQUEUED;
}

static int do_req_filebacked(struct loop_device *lo, struct request *rq)
{
	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
	loff_t pos = ((loff_t) blk_rq_pos(rq) << 9) + lo->lo_offset;

	switch (req_op(rq)) {
	case REQ_OP_FLUSH:
		return lo_req_flush(lo, rq);
	case REQ_OP_WRITE_ZEROES:
		/*
		 * If the caller doesn't want deallocation, call zeroout to
		 * write zeroes the range.  Otherwise, punch them out.
		 */
		return lo_fallocate(lo, rq, pos,
			(rq->cmd_flags & REQ_NOUNMAP) ?
				FALLOC_FL_ZERO_RANGE :
				FALLOC_FL_PUNCH_HOLE);
	case REQ_OP_DISCARD:
		return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE);
	case REQ_OP_WRITE:
		return lo_rw_aio(lo, cmd, pos, ITER_SOURCE);
	case REQ_OP_READ:
		return lo_rw_aio(lo, cmd, pos, ITER_DEST);
	default:
		WARN_ON_ONCE(1);
		return -EIO;
	}
}

static void loop_reread_partitions(struct loop_device *lo)
{
	int rc;

	mutex_lock(&lo->lo_disk->open_mutex);
	rc = bdev_disk_changed(lo->lo_disk, false);
	mutex_unlock(&lo->lo_disk->open_mutex);
	if (rc)
		pr_warn("%s: partition scan of loop%d (%s) failed (rc=%d)\n",
			__func__, lo->lo_number, lo->lo_file_name, rc);
}

static unsigned int loop_query_min_dio_size(struct loop_device *lo)
{
	struct file *file = lo->lo_backing_file;
	struct block_device *sb_bdev = file->f_mapping->host->i_sb->s_bdev;
	struct kstat st;

	/*
	 * Use the minimal dio alignment of the file system if provided.
	 */
	if (!vfs_getattr(&file->f_path, &st, STATX_DIOALIGN, 0) &&
	    (st.result_mask & STATX_DIOALIGN))
		return st.dio_offset_align;

	/*
	 * In a perfect world this wouldn't be needed, but as of Linux 6.13 only
	 * a handful of file systems support the STATX_DIOALIGN flag.
	 */
	if (sb_bdev)
		return bdev_logical_block_size(sb_bdev);
	return SECTOR_SIZE;
}

static inline int is_loop_device(struct file *file)
{
	struct inode *i = file->f_mapping->host;

	return i && S_ISBLK(i->i_mode) && imajor(i) == LOOP_MAJOR;
}

static int loop_validate_file(struct file *file, struct block_device *bdev)
{
	struct inode	*inode = file->f_mapping->host;
	struct file	*f = file;

	/* Avoid recursion */
	while (is_loop_device(f)) {
		struct loop_device *l;

		lockdep_assert_held(&loop_validate_mutex);
		if (f->f_mapping->host->i_rdev == bdev->bd_dev)
			return -EBADF;

		l = I_BDEV(f->f_mapping->host)->bd_disk->private_data;
		if (l->lo_state != Lo_bound)
			return -EINVAL;
		/* Order wrt setting lo->lo_backing_file in loop_configure(). */
		rmb();
		f = l->lo_backing_file;
	}
	if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
		return -EINVAL;
	return 0;
}

static void loop_assign_backing_file(struct loop_device *lo, struct file *file)
{
	lo->lo_backing_file = file;
	lo->old_gfp_mask = mapping_gfp_mask(file->f_mapping);
	mapping_set_gfp_mask(file->f_mapping,
			lo->old_gfp_mask & ~(__GFP_IO | __GFP_FS));
	if (lo->lo_backing_file->f_flags & O_DIRECT)
		lo->lo_flags |= LO_FLAGS_DIRECT_IO;
	lo->lo_min_dio_size = loop_query_min_dio_size(lo);
}

static int loop_check_backing_file(struct file *file)
{
	if (!file->f_op->read_iter)
		return -EINVAL;

	if ((file->f_mode & FMODE_WRITE) && !file->f_op->write_iter)
		return -EINVAL;

	return 0;
}

/*
 * loop_change_fd switched the backing store of a loopback device to
 * a new file. This is useful for operating system installers to free up
 * the original file and in High Availability environments to switch to
 * an alternative location for the content in case of server meltdown.
 * This can only work if the loop device is used read-only, and if the
 * new backing store is the same size and type as the old backing store.
 */
static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
			  unsigned int arg)
{
	struct file *file = fget(arg);
	struct file *old_file;
	unsigned int memflags;
	int error;
	bool partscan;
	bool is_loop;

	if (!file)
		return -EBADF;

	error = loop_check_backing_file(file);
	if (error) {
		fput(file);
		return error;
	}

	/* suppress uevents while reconfiguring the device */
	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1);

	is_loop = is_loop_device(file);
	error = loop_global_lock_killable(lo, is_loop);
	if (error)
		goto out_putf;
	error = -ENXIO;
	if (lo->lo_state != Lo_bound)
		goto out_err;

	/* the loop device has to be read-only */
	error = -EINVAL;
	if (!(lo->lo_flags & LO_FLAGS_READ_ONLY))
		goto out_err;

	error = loop_validate_file(file, bdev);
	if (error)
		goto out_err;

	old_file = lo->lo_backing_file;

	error = -EINVAL;

	/* size of the new backing store needs to be the same */
	if (lo_calculate_size(lo, file) != lo_calculate_size(lo, old_file))
		goto out_err;

	/*
	 * We might switch to direct I/O mode for the loop device, write back
	 * all dirty data the page cache now that so that the individual I/O
	 * operations don't have to do that.
	 */
	vfs_fsync(file, 0);

	/* and ... switch */
	disk_force_media_change(lo->lo_disk);
	memflags = blk_mq_freeze_queue(lo->lo_queue);
	mapping_set_gfp_mask(old_file->f_mapping, lo->old_gfp_mask);
	loop_assign_backing_file(lo, file);
	loop_update_dio(lo);
	blk_mq_unfreeze_queue(lo->lo_queue, memflags);
	partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
	loop_global_unlock(lo, is_loop);

	/*
	 * Flush loop_validate_file() before fput(), for l->lo_backing_file
	 * might be pointing at old_file which might be the last reference.
	 */
	if (!is_loop) {
		mutex_lock(&loop_validate_mutex);
		mutex_unlock(&loop_validate_mutex);
	}
	/*
	 * We must drop file reference outside of lo_mutex as dropping
	 * the file ref can take open_mutex which creates circular locking
	 * dependency.
	 */
	fput(old_file);
	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 0);
	if (partscan)
		loop_reread_partitions(lo);

	error = 0;
done:
	kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);
	return error;

out_err:
	loop_global_unlock(lo, is_loop);
out_putf:
	fput(file);
	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 0);
	goto done;
}

/* loop sysfs attributes */

static ssize_t loop_attr_show(struct device *dev, char *page,
			      ssize_t (*callback)(struct loop_device *, char *))
{
	struct gendisk *disk = dev_to_disk(dev);
	struct loop_device *lo = disk->private_data;

	return callback(lo, page);
}

#define LOOP_ATTR_RO(_name)						\
static ssize_t loop_attr_##_name##_show(struct loop_device *, char *);	\
static ssize_t loop_attr_do_show_##_name(struct device *d,		\
				struct device_attribute *attr, char *b)	\
{									\
	return loop_attr_show(d, b, loop_attr_##_name##_show);		\
}									\
static struct device_attribute loop_attr_##_name =			\
	__ATTR(_name, 0444, loop_attr_do_show_##_name, NULL);

static ssize_t loop_attr_backing_file_show(struct loop_device *lo, char *buf)
{
	ssize_t ret;
	char *p = NULL;

	spin_lock_irq(&lo->lo_lock);
	if (lo->lo_backing_file)
		p = file_path(lo->lo_backing_file, buf, PAGE_SIZE - 1);
	spin_unlock_irq(&lo->lo_lock);

	if (IS_ERR_OR_NULL(p))
		ret = PTR_ERR(p);
	else {
		ret = strlen(p);
		memmove(buf, p, ret);
		buf[ret++] = '\n';
		buf[ret] = 0;
	}

	return ret;
}

static ssize_t loop_attr_offset_show(struct loop_device *lo, char *buf)
{
	return sysfs_emit(buf, "%llu\n", (unsigned long long)lo->lo_offset);
}

static ssize_t loop_attr_sizelimit_show(struct loop_device *lo, char *buf)
{
	return sysfs_emit(buf, "%llu\n", (unsigned long long)lo->lo_sizelimit);
}

static ssize_t loop_attr_autoclear_show(struct loop_device *lo, char *buf)
{
	int autoclear = (lo->lo_flags & LO_FLAGS_AUTOCLEAR);

	return sysfs_emit(buf, "%s\n", autoclear ? "1" : "0");
}

static ssize_t loop_attr_partscan_show(struct loop_device *lo, char *buf)
{
	int partscan = (lo->lo_flags & LO_FLAGS_PARTSCAN);

	return sysfs_emit(buf, "%s\n", partscan ? "1" : "0");
}

static ssize_t loop_attr_dio_show(struct loop_device *lo, char *buf)
{
	int dio = (lo->lo_flags & LO_FLAGS_DIRECT_IO);

	return sysfs_emit(buf, "%s\n", dio ? "1" : "0");
}

LOOP_ATTR_RO(backing_file);
LOOP_ATTR_RO(offset);
LOOP_ATTR_RO(sizelimit);
LOOP_ATTR_RO(autoclear);
LOOP_ATTR_RO(partscan);
LOOP_ATTR_RO(dio);

static struct attribute *loop_attrs[] = {
	&loop_attr_backing_file.attr,
	&loop_attr_offset.attr,
	&loop_attr_sizelimit.attr,
	&loop_attr_autoclear.attr,
	&loop_attr_partscan.attr,
	&loop_attr_dio.attr,
	NULL,
};

static struct attribute_group loop_attribute_group = {
	.name = "loop",
	.attrs= loop_attrs,
};

static void loop_sysfs_init(struct loop_device *lo)
{
	lo->sysfs_inited = !sysfs_create_group(&disk_to_dev(lo->lo_disk)->kobj,
						&loop_attribute_group);
}

static void loop_sysfs_exit(struct loop_device *lo)
{
	if (lo->sysfs_inited)
		sysfs_remove_group(&disk_to_dev(lo->lo_disk)->kobj,
				   &loop_attribute_group);
}

static void loop_get_discard_config(struct loop_device *lo,
				    u32 *granularity, u32 *max_discard_sectors)
{
	struct file *file = lo->lo_backing_file;
	struct inode *inode = file->f_mapping->host;
	struct kstatfs sbuf;

	/*
	 * If the backing device is a block device, mirror its zeroing
	 * capability. Set the discard sectors to the block device's zeroing
	 * capabilities because loop discards result in blkdev_issue_zeroout(),
	 * not blkdev_issue_discard(). This maintains consistent behavior with
	 * file-backed loop devices: discarded regions read back as zero.
	 */
	if (S_ISBLK(inode->i_mode)) {
		struct block_device *bdev = I_BDEV(inode);

		*max_discard_sectors = bdev_write_zeroes_sectors(bdev);
		*granularity = bdev_discard_granularity(bdev);

	/*
	 * We use punch hole to reclaim the free space used by the
	 * image a.k.a. discard.
	 */
	} else if (file->f_op->fallocate && !vfs_statfs(&file->f_path, &sbuf)) {
		*max_discard_sectors = UINT_MAX >> 9;
		*granularity = sbuf.f_bsize;
	}
}

struct loop_worker {
	struct rb_node rb_node;
	struct work_struct work;
	struct list_head cmd_list;
	struct list_head idle_list;
	struct loop_device *lo;
	struct cgroup_subsys_state *blkcg_css;
	unsigned long last_ran_at;
};

static void loop_workfn(struct work_struct *work);

#ifdef CONFIG_BLK_CGROUP
static inline int queue_on_root_worker(struct cgroup_subsys_state *css)
{
	return !css || css == blkcg_root_css;
}
#else
static inline int queue_on_root_worker(struct cgroup_subsys_state *css)
{
	return !css;
}
#endif

static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
{
	struct rb_node **node, *parent = NULL;
	struct loop_worker *cur_worker, *worker = NULL;
	struct work_struct *work;
	struct list_head *cmd_list;

	spin_lock_irq(&lo->lo_work_lock);

	if (queue_on_root_worker(cmd->blkcg_css))
		goto queue_work;

	node = &lo->worker_tree.rb_node;

	while (*node) {
		parent = *node;
		cur_worker = container_of(*node, struct loop_worker, rb_node);
		if (cur_worker->blkcg_css == cmd->blkcg_css) {
			worker = cur_worker;
			break;
		} else if ((long)cur_worker->blkcg_css < (long)cmd->blkcg_css) {
			node = &(*node)->rb_left;
		} else {
			node = &(*node)->rb_right;
		}
	}
	if (worker)
		goto queue_work;

	worker = kzalloc(sizeof(struct loop_worker), GFP_NOWAIT);
	/*
	 * In the event we cannot allocate a worker, just queue on the
	 * rootcg worker and issue the I/O as the rootcg
	 */
	if (!worker) {
		cmd->blkcg_css = NULL;
		if (cmd->memcg_css)
			css_put(cmd->memcg_css);
		cmd->memcg_css = NULL;
		goto queue_work;
	}

	worker->blkcg_css = cmd->blkcg_css;
	css_get(worker->blkcg_css);
	INIT_WORK(&worker->work, loop_workfn);
	INIT_LIST_HEAD(&worker->cmd_list);
	INIT_LIST_HEAD(&worker->idle_list);
	worker->lo = lo;
	rb_link_node(&worker->rb_node, parent, node);
	rb_insert_color(&worker->rb_node, &lo->worker_tree);
queue_work:
	if (worker) {
		/*
		 * We need to remove from the idle list here while
		 * holding the lock so that the idle timer doesn't
		 * free the worker
		 */
		if (!list_empty(&worker->idle_list))
			list_del_init(&worker->idle_list);
		work = &worker->work;
		cmd_list = &worker->cmd_list;
	} else {
		work = &lo->rootcg_work;
		cmd_list = &lo->rootcg_cmd_list;
	}
	list_add_tail(&cmd->list_entry, cmd_list);
	queue_work(lo->workqueue, work);
	spin_unlock_irq(&lo->lo_work_lock);
}

static void loop_set_timer(struct loop_device *lo)
{
	timer_reduce(&lo->timer, jiffies + LOOP_IDLE_WORKER_TIMEOUT);
}

static void loop_free_idle_workers(struct loop_device *lo, bool delete_all)
{
	struct loop_worker *pos, *worker;

	spin_lock_irq(&lo->lo_work_lock);
	list_for_each_entry_safe(worker, pos, &lo->idle_worker_list,
				idle_list) {
		if (!delete_all &&
		    time_is_after_jiffies(worker->last_ran_at +
					  LOOP_IDLE_WORKER_TIMEOUT))
			break;
		list_del(&worker->idle_list);
		rb_erase(&worker->rb_node, &lo->worker_tree);
		css_put(worker->blkcg_css);
		kfree(worker);
	}
	if (!list_empty(&lo->idle_worker_list))
		loop_set_timer(lo);
	spin_unlock_irq(&lo->lo_work_lock);
}

static void loop_free_idle_workers_timer(struct timer_list *timer)
{
	struct loop_device *lo = container_of(timer, struct loop_device, timer);

	return loop_free_idle_workers(lo, false);
}

/**
 * loop_set_status_from_info - configure device from loop_info
 * @lo: struct loop_device to configure
 * @info: struct loop_info64 to configure the device with
 *
 * Configures the loop device parameters according to the passed
 * in loop_info64 configuration.
 */
static int
loop_set_status_from_info(struct loop_device *lo,
			  const struct loop_info64 *info)
{
	if ((unsigned int) info->lo_encrypt_key_size > LO_KEY_SIZE)
		return -EINVAL;

	switch (info->lo_encrypt_type) {
	case LO_CRYPT_NONE:
		break;
	case LO_CRYPT_XOR:
		pr_warn("support for the xor transformation has been removed.\n");
		return -EINVAL;
	case LO_CRYPT_CRYPTOAPI:
		pr_warn("support for cryptoloop has been removed.  Use dm-crypt instead.\n");
		return -EINVAL;
	default:
		return -EINVAL;
	}

	/* Avoid assigning overflow values */
	if (info->lo_offset > LLONG_MAX || info->lo_sizelimit > LLONG_MAX)
		return -EOVERFLOW;

	lo->lo_offset = info->lo_offset;
	lo->lo_sizelimit = info->lo_sizelimit;

	memcpy(lo->lo_file_name, info->lo_file_name, LO_NAME_SIZE);
	lo->lo_file_name[LO_NAME_SIZE-1] = 0;
	return 0;
}

static unsigned int loop_default_blocksize(struct loop_device *lo)
{
	/* In case of direct I/O, match underlying minimum I/O size */
	if (lo->lo_flags & LO_FLAGS_DIRECT_IO)
		return lo->lo_min_dio_size;
	return SECTOR_SIZE;
}

static void loop_update_limits(struct loop_device *lo, struct queue_limits *lim,
		unsigned int bsize)
{
	struct file *file = lo->lo_backing_file;
	struct inode *inode = file->f_mapping->host;
	struct block_device *backing_bdev = NULL;
	u32 granularity = 0, max_discard_sectors = 0;

	if (S_ISBLK(inode->i_mode))
		backing_bdev = I_BDEV(inode);
	else if (inode->i_sb->s_bdev)
		backing_bdev = inode->i_sb->s_bdev;

	if (!bsize)
		bsize = loop_default_blocksize(lo);

	loop_get_discard_config(lo, &granularity, &max_discard_sectors);

	lim->logical_block_size = bsize;
	lim->physical_block_size = bsize;
	lim->io_min = bsize;
	lim->features &= ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_ROTATIONAL);
	if (file->f_op->fsync && !(lo->lo_flags & LO_FLAGS_READ_ONLY))
		lim->features |= BLK_FEAT_WRITE_CACHE;
	if (backing_bdev && !bdev_nonrot(backing_bdev))
		lim->features |= BLK_FEAT_ROTATIONAL;
	lim->max_hw_discard_sectors = max_discard_sectors;
	lim->max_write_zeroes_sectors = max_discard_sectors;
	if (max_discard_sectors)
		lim->discard_granularity = granularity;
	else
		lim->discard_granularity = 0;
}

static int loop_configure(struct loop_device *lo, blk_mode_t mode,
			  struct block_device *bdev,
			  const struct loop_config *config)
{
	struct file *file = fget(config->fd);
	struct queue_limits lim;
	int error;
	loff_t size;
	bool partscan;
	bool is_loop;

	if (!file)
		return -EBADF;

	error = loop_check_backing_file(file);
	if (error) {
		fput(file);
		return error;
	}

	is_loop = is_loop_device(file);

	/* This is safe, since we have a reference from open(). */
	__module_get(THIS_MODULE);

	/*
	 * If we don't hold exclusive handle for the device, upgrade to it
	 * here to avoid changing device under exclusive owner.
	 */
	if (!(mode & BLK_OPEN_EXCL)) {
		error = bd_prepare_to_claim(bdev, loop_configure, NULL);
		if (error)
			goto out_putf;
	}

	error = loop_global_lock_killable(lo, is_loop);
	if (error)
		goto out_bdev;

	error = -EBUSY;
	if (lo->lo_state != Lo_unbound)
		goto out_unlock;

	error = loop_validate_file(file, bdev);
	if (error)
		goto out_unlock;

	if ((config->info.lo_flags & ~LOOP_CONFIGURE_SETTABLE_FLAGS) != 0) {
		error = -EINVAL;
		goto out_unlock;
	}

	error = loop_set_status_from_info(lo, &config->info);
	if (error)
		goto out_unlock;
	lo->lo_flags = config->info.lo_flags;

	if (!(file->f_mode & FMODE_WRITE) || !(mode & BLK_OPEN_WRITE) ||
	    !file->f_op->write_iter)
		lo->lo_flags |= LO_FLAGS_READ_ONLY;

	if (!lo->workqueue) {
		lo->workqueue = alloc_workqueue("loop%d",
						WQ_UNBOUND | WQ_FREEZABLE,
						0, lo->lo_number);
		if (!lo->workqueue) {
			error = -ENOMEM;
			goto out_unlock;
		}
	}

	/* suppress uevents while reconfiguring the device */
	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1);

	disk_force_media_change(lo->lo_disk);
	set_disk_ro(lo->lo_disk, (lo->lo_flags & LO_FLAGS_READ_ONLY) != 0);

	lo->lo_device = bdev;
	loop_assign_backing_file(lo, file);

	lim = queue_limits_start_update(lo->lo_queue);
	loop_update_limits(lo, &lim, config->block_size);
	/* No need to freeze the queue as the device isn't bound yet. */
	error = queue_limits_commit_update(lo->lo_queue, &lim);
	if (error)
		goto out_unlock;

	/*
	 * We might switch to direct I/O mode for the loop device, write back
	 * all dirty data the page cache now that so that the individual I/O
	 * operations don't have to do that.
	 */
	vfs_fsync(file, 0);

	loop_update_dio(lo);
	loop_sysfs_init(lo);

	size = lo_calculate_size(lo, file);
	loop_set_size(lo, size);

	/* Order wrt reading lo_state in loop_validate_file(). */
	wmb();

	WRITE_ONCE(lo->lo_state, Lo_bound);
	if (part_shift)
		lo->lo_flags |= LO_FLAGS_PARTSCAN;
	partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
	if (partscan)
		clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);

	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 0);
	kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);

	loop_global_unlock(lo, is_loop);
	if (partscan)
		loop_reread_partitions(lo);

	if (!(mode & BLK_OPEN_EXCL))
		bd_abort_claiming(bdev, loop_configure);

	return 0;

out_unlock:
	loop_global_unlock(lo, is_loop);
out_bdev:
	if (!(mode & BLK_OPEN_EXCL))
		bd_abort_claiming(bdev, loop_configure);
out_putf:
	fput(file);
	/* This is safe: open() is still holding a reference. */
	module_put(THIS_MODULE);
	return error;
}

static void __loop_clr_fd(struct loop_device *lo)
{
	struct queue_limits lim;
	struct file *filp;
	gfp_t gfp = lo->old_gfp_mask;

	spin_lock_irq(&lo->lo_lock);
	filp = lo->lo_backing_file;
	lo->lo_backing_file = NULL;
	spin_unlock_irq(&lo->lo_lock);

	lo->lo_device = NULL;
	lo->lo_offset = 0;
	lo->lo_sizelimit = 0;
	memset(lo->lo_file_name, 0, LO_NAME_SIZE);

	/*
	 * Reset the block size to the default.
	 *
	 * No queue freezing needed because this is called from the final
	 * ->release call only, so there can't be any outstanding I/O.
	 */
	lim = queue_limits_start_update(lo->lo_queue);
	lim.logical_block_size = SECTOR_SIZE;
	lim.physical_block_size = SECTOR_SIZE;
	lim.io_min = SECTOR_SIZE;
	queue_limits_commit_update(lo->lo_queue, &lim);

	invalidate_disk(lo->lo_disk);
	loop_sysfs_exit(lo);
	/* let user-space know about this change */
	kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);
	mapping_set_gfp_mask(filp->f_mapping, gfp);
	/* This is safe: open() is still holding a reference. */
	module_put(THIS_MODULE);

	disk_force_media_change(lo->lo_disk);

	if (lo->lo_flags & LO_FLAGS_PARTSCAN) {
		int err;

		/*
		 * open_mutex has been held already in release path, so don't
		 * acquire it if this function is called in such case.
		 *
		 * If the reread partition isn't from release path, lo_refcnt
		 * must be at least one and it can only become zero when the
		 * current holder is released.
		 */
		err = bdev_disk_changed(lo->lo_disk, false);
		if (err)
			pr_warn("%s: partition scan of loop%d failed (rc=%d)\n",
				__func__, lo->lo_number, err);
		/* Device is gone, no point in returning error */
	}

	/*
	 * lo->lo_state is set to Lo_unbound here after above partscan has
	 * finished. There cannot be anybody else entering __loop_clr_fd() as
	 * Lo_rundown state protects us from all the other places trying to
	 * change the 'lo' device.
	 */
	lo->lo_flags = 0;
	if (!part_shift)
		set_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
	mutex_lock(&lo->lo_mutex);
	WRITE_ONCE(lo->lo_state, Lo_unbound);
	mutex_unlock(&lo->lo_mutex);

	/*
	 * Need not hold lo_mutex to fput backing file. Calling fput holding
	 * lo_mutex triggers a circular lock dependency possibility warning as
	 * fput can take open_mutex which is usually taken before lo_mutex.
	 */
	fput(filp);
}

static int loop_clr_fd(struct loop_device *lo)
{
	int err;

	/*
	 * Since lo_ioctl() is called without locks held, it is possible that
	 * loop_configure()/loop_change_fd() and loop_clr_fd() run in parallel.
	 *
	 * Therefore, use global lock when setting Lo_rundown state in order to
	 * make sure that loop_validate_file() will fail if the "struct file"
	 * which loop_configure()/loop_change_fd() found via fget() was this
	 * loop device.
	 */
	err = loop_global_lock_killable(lo, true);
	if (err)
		return err;
	if (lo->lo_state != Lo_bound) {
		loop_global_unlock(lo, true);
		return -ENXIO;
	}
	/*
	 * Mark the device for removing the backing device on last close.
	 * If we are the only opener, also switch the state to roundown here to
	 * prevent new openers from coming in.
	 */

	lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
	if (disk_openers(lo->lo_disk) == 1)
		WRITE_ONCE(lo->lo_state, Lo_rundown);
	loop_global_unlock(lo, true);

	return 0;
}

static int
loop_set_status(struct loop_device *lo, blk_mode_t mode,
		struct block_device *bdev, const struct loop_info64 *info)
{
	int err;
	bool partscan = false;
	bool size_changed = false;
	unsigned int memflags;

	/*
	 * If we don't hold exclusive handle for the device, upgrade to it
	 * here to avoid changing device under exclusive owner.
	 */
	if (!(mode & BLK_OPEN_EXCL)) {
		err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
		if (err)
			goto out_reread_partitions;
	}

	err = mutex_lock_killable(&lo->lo_mutex);
	if (err)
		goto out_abort_claiming;

	if (lo->lo_state != Lo_bound) {
		err = -ENXIO;
		goto out_unlock;
	}

	if (lo->lo_offset != info->lo_offset ||
	    lo->lo_sizelimit != info->lo_sizelimit) {
		size_changed = true;
		sync_blockdev(lo->lo_device);
		invalidate_bdev(lo->lo_device);
	}

	/* I/O needs to be drained before changing lo_offset or lo_sizelimit */
	memflags = blk_mq_freeze_queue(lo->lo_queue);

	err = loop_set_status_from_info(lo, info);
	if (err)
		goto out_unfreeze;

	partscan = !(lo->lo_flags & LO_FLAGS_PARTSCAN) &&
		(info->lo_flags & LO_FLAGS_PARTSCAN);

	lo->lo_flags &= ~LOOP_SET_STATUS_CLEARABLE_FLAGS;
	lo->lo_flags |= (info->lo_flags & LOOP_SET_STATUS_SETTABLE_FLAGS);

	/* update the direct I/O flag if lo_offset changed */
	loop_update_dio(lo);

out_unfreeze:
	blk_mq_unfreeze_queue(lo->lo_queue, memflags);
	if (partscan)
		clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
	if (!err && size_changed) {
		loff_t new_size = lo_calculate_size(lo, lo->lo_backing_file);
		loop_set_size(lo, new_size);
	}
out_unlock:
	mutex_unlock(&lo->lo_mutex);
out_abort_claiming:
	if (!(mode & BLK_OPEN_EXCL))
		bd_abort_claiming(bdev, loop_set_status);
out_reread_partitions:
	if (partscan)
		loop_reread_partitions(lo);

	return err;
}

static int
loop_get_status(struct loop_device *lo, struct loop_info64 *info)
{
	struct path path;
	struct kstat stat;
	int ret;

	ret = mutex_lock_killable(&lo->lo_mutex);
	if (ret)
		return ret;
	if (lo->lo_state != Lo_bound) {
		mutex_unlock(&lo->lo_mutex);
		return -ENXIO;
	}

	memset(info, 0, sizeof(*info));
	info->lo_number = lo->lo_number;
	info->lo_offset = lo->lo_offset;
	info->lo_sizelimit = lo->lo_sizelimit;
	info->lo_flags = lo->lo_flags;
	memcpy(info->lo_file_name, lo->lo_file_name, LO_NAME_SIZE);

	/* Drop lo_mutex while we call into the filesystem. */
	path = lo->lo_backing_file->f_path;
	path_get(&path);
	mutex_unlock(&lo->lo_mutex);
	ret = vfs_getattr(&path, &stat, STATX_INO, AT_STATX_SYNC_AS_STAT);
	if (!ret) {
		info->lo_device = huge_encode_dev(stat.dev);
		info->lo_inode = stat.ino;
		info->lo_rdevice = huge_encode_dev(stat.rdev);
	}
	path_put(&path);
	return ret;
}

static void
loop_info64_from_old(const struct loop_info *info, struct loop_info64 *info64)
{
	memset(info64, 0, sizeof(*info64));
	info64->lo_number = info->lo_number;
	info64->lo_device = info->lo_device;
	info64->lo_inode = info->lo_inode;
	info64->lo_rdevice = info->lo_rdevice;
	info64->lo_offset = info->lo_offset;
	info64->lo_sizelimit = 0;
	info64->lo_flags = info->lo_flags;
	memcpy(info64->lo_file_name, info->lo_name, LO_NAME_SIZE);
}

static int
loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
{
	memset(info, 0, sizeof(*info));
	info->lo_number = info64->lo_number;
	info->lo_device = info64->lo_device;
	info->lo_inode = info64->lo_inode;
	info->lo_rdevice = info64->lo_rdevice;
	info->lo_offset = info64->lo_offset;
	info->lo_flags = info64->lo_flags;
	memcpy(info->lo_name, info64->lo_file_name, LO_NAME_SIZE);

	/* error in case values were truncated */
	if (info->lo_device != info64->lo_device ||
	    info->lo_rdevice != info64->lo_rdevice ||
	    info->lo_inode != info64->lo_inode ||
	    info->lo_offset != info64->lo_offset)
		return -EOVERFLOW;

	return 0;
}

static int
loop_set_status_old(struct loop_device *lo, blk_mode_t mode,
		    struct block_device *bdev,
		    const struct loop_info __user *arg)
{
	struct loop_info info;
	struct loop_info64 info64;

	if (copy_from_user(&info, arg, sizeof (struct loop_info)))
		return -EFAULT;
	loop_info64_from_old(&info, &info64);
	return loop_set_status(lo, mode, bdev, &info64);
}

static int
loop_set_status64(struct loop_device *lo, blk_mode_t mode,
		  struct block_device *bdev,
		  const struct loop_info64 __user *arg)
{
	struct loop_info64 info64;

	if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
		return -EFAULT;
	return loop_set_status(lo, mode, bdev, &info64);
}

static int
loop_get_status_old(struct loop_device *lo, struct loop_info __user *arg) {
	struct loop_info info;
	struct loop_info64 info64;
	int err;

	if (!arg)
		return -EINVAL;
	err = loop_get_status(lo, &info64);
	if (!err)
		err = loop_info64_to_old(&info64, &info);
	if (!err && copy_to_user(arg, &info, sizeof(info)))
		err = -EFAULT;

	return err;
}

static int
loop_get_status64(struct loop_device *lo, struct loop_info64 __user *arg) {
	struct loop_info64 info64;
	int err;

	if (!arg)
		return -EINVAL;
	err = loop_get_status(lo, &info64);
	if (!err && copy_to_user(arg, &info64, sizeof(info64)))
		err = -EFAULT;

	return err;
}

static int loop_set_capacity(struct loop_device *lo)
{
	loff_t size;

	if (unlikely(lo->lo_state != Lo_bound))
		return -ENXIO;

	size = lo_calculate_size(lo, lo->lo_backing_file);
	loop_set_size(lo, size);

	return 0;
}

static int loop_set_dio(struct loop_device *lo, unsigned long arg)
{
	bool use_dio = !!arg;
	unsigned int memflags;

	if (lo->lo_state != Lo_bound)
		return -ENXIO;
	if (use_dio == !!(lo->lo_flags & LO_FLAGS_DIRECT_IO))
		return 0;

	if (use_dio) {
		if (!lo_can_use_dio(lo))
			return -EINVAL;
		/* flush dirty pages before starting to use direct I/O */
		vfs_fsync(lo->lo_backing_file, 0);
	}

	memflags = blk_mq_freeze_queue(lo->lo_queue);
	if (use_dio)
		lo->lo_flags |= LO_FLAGS_DIRECT_IO;
	else
		lo->lo_flags &= ~LO_FLAGS_DIRECT_IO;
	blk_mq_unfreeze_queue(lo->lo_queue, memflags);
	return 0;
}

static int loop_set_block_size(struct loop_device *lo, blk_mode_t mode,
			       struct block_device *bdev, unsigned long arg)
{
	struct queue_limits lim;
	unsigned int memflags;
	int err = 0;

	/*
	 * If we don't hold exclusive handle for the device, upgrade to it
	 * here to avoid changing device under exclusive owner.
	 */
	if (!(mode & BLK_OPEN_EXCL)) {
		err = bd_prepare_to_claim(bdev, loop_set_block_size, NULL);
		if (err)
			return err;
	}

	err = mutex_lock_killable(&lo->lo_mutex);
	if (err)
		goto abort_claim;

	if (lo->lo_state != Lo_bound) {
		err = -ENXIO;
		goto unlock;
	}

	if (lo->lo_queue->limits.logical_block_size == arg)
		goto unlock;

	sync_blockdev(lo->lo_device);
	invalidate_bdev(lo->lo_device);

	lim = queue_limits_start_update(lo->lo_queue);
	loop_update_limits(lo, &lim, arg);

	memflags = blk_mq_freeze_queue(lo->lo_queue);
	err = queue_limits_commit_update(lo->lo_queue, &lim);
	loop_update_dio(lo);
	blk_mq_unfreeze_queue(lo->lo_queue, memflags);

unlock:
	mutex_unlock(&lo->lo_mutex);
abort_claim:
	if (!(mode & BLK_OPEN_EXCL))
		bd_abort_claiming(bdev, loop_set_block_size);
	return err;
}

static int lo_simple_ioctl(struct loop_device *lo, unsigned int cmd,
			   unsigned long arg)
{
	int err;

	err = mutex_lock_killable(&lo->lo_mutex);
	if (err)
		return err;
	switch (cmd) {
	case LOOP_SET_CAPACITY:
		err = loop_set_capacity(lo);
		break;
	case LOOP_SET_DIRECT_IO:
		err = loop_set_dio(lo, arg);
		break;
	default:
		err = -EINVAL;
	}
	mutex_unlock(&lo->lo_mutex);
	return err;
}

static int lo_ioctl(struct block_device *bdev, blk_mode_t mode,
	unsigned int cmd, unsigned long arg)
{
	struct loop_device *lo = bdev->bd_disk->private_data;
	void __user *argp = (void __user *) arg;
	int err;

	switch (cmd) {
	case LOOP_SET_FD: {
		/*
		 * Legacy case - pass in a zeroed out struct loop_config with
		 * only the file descriptor set , which corresponds with the
		 * default parameters we'd have used otherwise.
		 */
		struct loop_config config;

		memset(&config, 0, sizeof(config));
		config.fd = arg;

		return loop_configure(lo, mode, bdev, &config);
	}
	case LOOP_CONFIGURE: {
		struct loop_config config;

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

		return loop_configure(lo, mode, bdev, &config);
	}
	case LOOP_CHANGE_FD:
		return loop_change_fd(lo, bdev, arg);
	case LOOP_CLR_FD:
		return loop_clr_fd(lo);
	case LOOP_SET_STATUS:
		err = -EPERM;
		if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
			err = loop_set_status_old(lo, mode, bdev, argp);
		break;
	case LOOP_GET_STATUS:
		return loop_get_status_old(lo, argp);
	case LOOP_SET_STATUS64:
		err = -EPERM;
		if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
			err = loop_set_status64(lo, mode, bdev, argp);
		break;
	case LOOP_GET_STATUS64:
		return loop_get_status64(lo, argp);
	case LOOP_SET_BLOCK_SIZE:
		if (!(mode & BLK_OPEN_WRITE) && !capable(CAP_SYS_ADMIN))
			return -EPERM;
		return loop_set_block_size(lo, mode, bdev, arg);
	case LOOP_SET_CAPACITY:
	case LOOP_SET_DIRECT_IO:
		if (!(mode & BLK_OPEN_WRITE) && !capable(CAP_SYS_ADMIN))
			return -EPERM;
		fallthrough;
	default:
		err = lo_simple_ioctl(lo, cmd, arg);
		break;
	}

	return err;
}

#ifdef CONFIG_COMPAT
struct compat_loop_info {
	compat_int_t	lo_number;      /* ioctl r/o */
	compat_dev_t	lo_device;      /* ioctl r/o */
	compat_ulong_t	lo_inode;       /* ioctl r/o */
	compat_dev_t	lo_rdevice;     /* ioctl r/o */
	compat_int_t	lo_offset;
	compat_int_t	lo_encrypt_type;        /* obsolete, ignored */
	compat_int_t	lo_encrypt_key_size;    /* ioctl w/o */
	compat_int_t	lo_flags;       /* ioctl r/o */
	char		lo_name[LO_NAME_SIZE];
	unsigned char	lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
	compat_ulong_t	lo_init[2];
	char		reserved[4];
};

/*
 * Transfer 32-bit compatibility structure in userspace to 64-bit loop info
 * - noinlined to reduce stack space usage in main part of driver
 */
static noinline int
loop_info64_from_compat(const struct compat_loop_info __user *arg,
			struct loop_info64 *info64)
{
	struct compat_loop_info info;

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

	memset(info64, 0, sizeof(*info64));
	info64->lo_number = info.lo_number;
	info64->lo_device = info.lo_device;
	info64->lo_inode = info.lo_inode;
	info64->lo_rdevice = info.lo_rdevice;
	info64->lo_offset = info.lo_offset;
	info64->lo_sizelimit = 0;
	info64->lo_flags = info.lo_flags;
	memcpy(info64->lo_file_name, info.lo_name, LO_NAME_SIZE);
	return 0;
}

/*
 * Transfer 64-bit loop info to 32-bit compatibility structure in userspace
 * - noinlined to reduce stack space usage in main part of driver
 */
static noinline int
loop_info64_to_compat(const struct loop_info64 *info64,
		      struct compat_loop_info __user *arg)
{
	struct compat_loop_info info;

	memset(&info, 0, sizeof(info));
	info.lo_number = info64->lo_number;
	info.lo_device = info64->lo_device;
	info.lo_inode = info64->lo_inode;
	info.lo_rdevice = info64->lo_rdevice;
	info.lo_offset = info64->lo_offset;
	info.lo_flags = info64->lo_flags;
	memcpy(info.lo_name, info64->lo_file_name, LO_NAME_SIZE);

	/* error in case values were truncated */
	if (info.lo_device != info64->lo_device ||
	    info.lo_rdevice != info64->lo_rdevice ||
	    info.lo_inode != info64->lo_inode ||
	    info.lo_offset != info64->lo_offset)
		return -EOVERFLOW;

	if (copy_to_user(arg, &info, sizeof(info)))
		return -EFAULT;
	return 0;
}

static int
loop_set_status_compat(struct loop_device *lo, blk_mode_t mode,
		    struct block_device *bdev,
		    const struct compat_loop_info __user *arg)
{
	struct loop_info64 info64;
	int ret;

	ret = loop_info64_from_compat(arg, &info64);
	if (ret < 0)
		return ret;
	return loop_set_status(lo, mode, bdev, &info64);
}

static int
loop_get_status_compat(struct loop_device *lo,
		       struct compat_loop_info __user *arg)
{
	struct loop_info64 info64;
	int err;

	if (!arg)
		return -EINVAL;
	err = loop_get_status(lo, &info64);
	if (!err)
		err = loop_info64_to_compat(&info64, arg);
	return err;
}

static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode,
			   unsigned int cmd, unsigned long arg)
{
	struct loop_device *lo = bdev->bd_disk->private_data;
	int err;

	switch(cmd) {
	case LOOP_SET_STATUS:
		err = loop_set_status_compat(lo, mode, bdev,
			     (const struct compat_loop_info __user *)arg);
		break;
	case LOOP_GET_STATUS:
		err = loop_get_status_compat(lo,
				     (struct compat_loop_info __user *)arg);
		break;
	case LOOP_SET_CAPACITY:
	case LOOP_CLR_FD:
	case LOOP_GET_STATUS64:
	case LOOP_SET_STATUS64:
	case LOOP_CONFIGURE:
		arg = (unsigned long) compat_ptr(arg);
		fallthrough;
	case LOOP_SET_FD:
	case LOOP_CHANGE_FD:
	case LOOP_SET_BLOCK_SIZE:
	case LOOP_SET_DIRECT_IO:
		err = lo_ioctl(bdev, mode, cmd, arg);
		break;
	default:
		err = -ENOIOCTLCMD;
		break;
	}
	return err;
}
#endif

static int lo_open(struct gendisk *disk, blk_mode_t mode)
{
	struct loop_device *lo = disk->private_data;
	int err;

	err = mutex_lock_killable(&lo->lo_mutex);
	if (err)
		return err;

	if (lo->lo_state == Lo_deleting || lo->lo_state == Lo_rundown)
		err = -ENXIO;
	mutex_unlock(&lo->lo_mutex);
	return err;
}

static void lo_release(struct gendisk *disk)
{
	struct loop_device *lo = disk->private_data;
	bool need_clear = false;

	if (disk_openers(disk) > 0)
		return;
	/*
	 * Clear the backing device information if this is the last close of
	 * a device that's been marked for auto clear, or on which LOOP_CLR_FD
	 * has been called.
	 */

	mutex_lock(&lo->lo_mutex);
	if (lo->lo_state == Lo_bound && (lo->lo_flags & LO_FLAGS_AUTOCLEAR))
		WRITE_ONCE(lo->lo_state, Lo_rundown);

	need_clear = (lo->lo_state == Lo_rundown);
	mutex_unlock(&lo->lo_mutex);

	if (need_clear)
		__loop_clr_fd(lo);
}

static void lo_free_disk(struct gendisk *disk)
{
	struct loop_device *lo = disk->private_data;

	if (lo->workqueue)
		destroy_workqueue(lo->workqueue);
	loop_free_idle_workers(lo, true);
	timer_shutdown_sync(&lo->timer);
	mutex_destroy(&lo->lo_mutex);
	kfree(lo);
}

static const struct block_device_operations lo_fops = {
	.owner =	THIS_MODULE,
	.open =         lo_open,
	.release =	lo_release,
	.ioctl =	lo_ioctl,
#ifdef CONFIG_COMPAT
	.compat_ioctl =	lo_compat_ioctl,
#endif
	.free_disk =	lo_free_disk,
};

/*
 * And now the modules code and kernel interface.
 */

/*
 * If max_loop is specified, create that many devices upfront.
 * This also becomes a hard limit. If max_loop is not specified,
 * the default isn't a hard limit (as before commit 85c50197716c
 * changed the default value from 0 for max_loop=0 reasons), just
 * create CONFIG_BLK_DEV_LOOP_MIN_COUNT loop devices at module
 * init time. Loop devices can be requested on-demand with the
 * /dev/loop-control interface, or be instantiated by accessing
 * a 'dead' device node.
 */
static int max_loop = CONFIG_BLK_DEV_LOOP_MIN_COUNT;

#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
static bool max_loop_specified;

static int max_loop_param_set_int(const char *val,
				  const struct kernel_param *kp)
{
	int ret;

	ret = param_set_int(val, kp);
	if (ret < 0)
		return ret;

	max_loop_specified = true;
	return 0;
}

static const struct kernel_param_ops max_loop_param_ops = {
	.set = max_loop_param_set_int,
	.get = param_get_int,
};

module_param_cb(max_loop, &max_loop_param_ops, &max_loop, 0444);
MODULE_PARM_DESC(max_loop, "Maximum number of loop devices");
#else
module_param(max_loop, int, 0444);
MODULE_PARM_DESC(max_loop, "Initial number of loop devices");
#endif

module_param(max_part, int, 0444);
MODULE_PARM_DESC(max_part, "Maximum number of partitions per loop device");

static int hw_queue_depth = LOOP_DEFAULT_HW_Q_DEPTH;

static int loop_set_hw_queue_depth(const char *s, const struct kernel_param *p)
{
	int qd, ret;

	ret = kstrtoint(s, 0, &qd);
	if (ret < 0)
		return ret;
	if (qd < 1)
		return -EINVAL;
	hw_queue_depth = qd;
	return 0;
}

static const struct kernel_param_ops loop_hw_qdepth_param_ops = {
	.set	= loop_set_hw_queue_depth,
	.get	= param_get_int,
};

device_param_cb(hw_queue_depth, &loop_hw_qdepth_param_ops, &hw_queue_depth, 0444);
MODULE_PARM_DESC(hw_queue_depth, "Queue depth for each hardware queue. Default: " __stringify(LOOP_DEFAULT_HW_Q_DEPTH));

MODULE_DESCRIPTION("Loopback device support");
MODULE_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(LOOP_MAJOR);

static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
		const struct blk_mq_queue_data *bd)
{
	struct request *rq = bd->rq;
	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
	struct loop_device *lo = rq->q->queuedata;

	blk_mq_start_request(rq);

	if (data_race(READ_ONCE(lo->lo_state)) != Lo_bound)
		return BLK_STS_IOERR;

	switch (req_op(rq)) {
	case REQ_OP_FLUSH:
	case REQ_OP_DISCARD:
	case REQ_OP_WRITE_ZEROES:
		cmd->use_aio = false;
		break;
	default:
		cmd->use_aio = lo->lo_flags & LO_FLAGS_DIRECT_IO;
		break;
	}

	/* always use the first bio's css */
	cmd->blkcg_css = NULL;
	cmd->memcg_css = NULL;
#ifdef CONFIG_BLK_CGROUP
	if (rq->bio) {
		cmd->blkcg_css = bio_blkcg_css(rq->bio);
#ifdef CONFIG_MEMCG
		if (cmd->blkcg_css) {
			cmd->memcg_css =
				cgroup_get_e_css(cmd->blkcg_css->cgroup,
						&memory_cgrp_subsys);
		}
#endif
	}
#endif
	loop_queue_work(lo, cmd);

	return BLK_STS_OK;
}

static void loop_handle_cmd(struct loop_cmd *cmd)
{
	struct cgroup_subsys_state *cmd_blkcg_css = cmd->blkcg_css;
	struct cgroup_subsys_state *cmd_memcg_css = cmd->memcg_css;
	struct request *rq = blk_mq_rq_from_pdu(cmd);
	const bool write = op_is_write(req_op(rq));
	struct loop_device *lo = rq->q->queuedata;
	int ret = 0;
	struct mem_cgroup *old_memcg = NULL;

	if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) {
		ret = -EIO;
		goto failed;
	}

	/* We can block in this context, so ignore REQ_NOWAIT. */
	if (rq->cmd_flags & REQ_NOWAIT)
		rq->cmd_flags &= ~REQ_NOWAIT;

	if (cmd_blkcg_css)
		kthread_associate_blkcg(cmd_blkcg_css);
	if (cmd_memcg_css)
		old_memcg = set_active_memcg(
			mem_cgroup_from_css(cmd_memcg_css));

	/*
	 * do_req_filebacked() may call blk_mq_complete_request() synchronously
	 * or asynchronously if using aio. Hence, do not touch 'cmd' after
	 * do_req_filebacked() has returned unless we are sure that 'cmd' has
	 * not yet been completed.
	 */
	ret = do_req_filebacked(lo, rq);

	if (cmd_blkcg_css)
		kthread_associate_blkcg(NULL);

	if (cmd_memcg_css) {
		set_active_memcg(old_memcg);
		css_put(cmd_memcg_css);
	}
 failed:
	/* complete non-aio request */
	if (ret != -EIOCBQUEUED) {
		if (ret == -EOPNOTSUPP)
			cmd->ret = ret;
		else
			cmd->ret = ret ? -EIO : 0;
		if (likely(!blk_should_fake_timeout(rq->q)))
			blk_mq_complete_request(rq);
	}
}

static void loop_process_work(struct loop_worker *worker,
			struct list_head *cmd_list, struct loop_device *lo)
{
	int orig_flags = current->flags;
	struct loop_cmd *cmd;

	current->flags |= PF_LOCAL_THROTTLE | PF_MEMALLOC_NOIO;
	spin_lock_irq(&lo->lo_work_lock);
	while (!list_empty(cmd_list)) {
		cmd = container_of(
			cmd_list->next, struct loop_cmd, list_entry);
		list_del(cmd_list->next);
		spin_unlock_irq(&lo->lo_work_lock);

		loop_handle_cmd(cmd);
		cond_resched();

		spin_lock_irq(&lo->lo_work_lock);
	}

	/*
	 * We only add to the idle list if there are no pending cmds
	 * *and* the worker will not run again which ensures that it
	 * is safe to free any worker on the idle list
	 */
	if (worker && !work_pending(&worker->work)) {
		worker->last_ran_at = jiffies;
		list_add_tail(&worker->idle_list, &lo->idle_worker_list);
		loop_set_timer(lo);
	}
	spin_unlock_irq(&lo->lo_work_lock);
	current->flags = orig_flags;
}

static void loop_workfn(struct work_struct *work)
{
	struct loop_worker *worker =
		container_of(work, struct loop_worker, work);
	loop_process_work(worker, &worker->cmd_list, worker->lo);
}

static void loop_rootcg_workfn(struct work_struct *work)
{
	struct loop_device *lo =
		container_of(work, struct loop_device, rootcg_work);
	loop_process_work(NULL, &lo->rootcg_cmd_list, lo);
}

static const struct blk_mq_ops loop_mq_ops = {
	.queue_rq       = loop_queue_rq,
	.complete	= lo_complete_rq,
};

static int loop_add(int i)
{
	struct queue_limits lim = {
		/*
		 * Random number picked from the historic block max_sectors cap.
		 */
		.max_hw_sectors		= 2560u,
	};
	struct loop_device *lo;
	struct gendisk *disk;
	int err;

	err = -ENOMEM;
	lo = kzalloc(sizeof(*lo), GFP_KERNEL);
	if (!lo)
		goto out;
	lo->worker_tree = RB_ROOT;
	INIT_LIST_HEAD(&lo->idle_worker_list);
	timer_setup(&lo->timer, loop_free_idle_workers_timer, TIMER_DEFERRABLE);
	WRITE_ONCE(lo->lo_state, Lo_unbound);

	err = mutex_lock_killable(&loop_ctl_mutex);
	if (err)
		goto out_free_dev;

	/* allocate id, if @id >= 0, we're requesting that specific id */
	if (i >= 0) {
		err = idr_alloc(&loop_index_idr, lo, i, i + 1, GFP_KERNEL);
		if (err == -ENOSPC)
			err = -EEXIST;
	} else {
		err = idr_alloc(&loop_index_idr, lo, 0, 0, GFP_KERNEL);
	}
	mutex_unlock(&loop_ctl_mutex);
	if (err < 0)
		goto out_free_dev;
	i = err;

	lo->tag_set.ops = &loop_mq_ops;
	lo->tag_set.nr_hw_queues = 1;
	lo->tag_set.queue_depth = hw_queue_depth;
	lo->tag_set.numa_node = NUMA_NO_NODE;
	lo->tag_set.cmd_size = sizeof(struct loop_cmd);
	lo->tag_set.flags = BLK_MQ_F_STACKING | BLK_MQ_F_NO_SCHED_BY_DEFAULT;
	lo->tag_set.driver_data = lo;

	err = blk_mq_alloc_tag_set(&lo->tag_set);
	if (err)
		goto out_free_idr;

	disk = lo->lo_disk = blk_mq_alloc_disk(&lo->tag_set, &lim, lo);
	if (IS_ERR(disk)) {
		err = PTR_ERR(disk);
		goto out_cleanup_tags;
	}
	lo->lo_queue = lo->lo_disk->queue;

	/*
	 * Disable partition scanning by default. The in-kernel partition
	 * scanning can be requested individually per-device during its
	 * setup. Userspace can always add and remove partitions from all
	 * devices. The needed partition minors are allocated from the
	 * extended minor space, the main loop device numbers will continue
	 * to match the loop minors, regardless of the number of partitions
	 * used.
	 *
	 * If max_part is given, partition scanning is globally enabled for
	 * all loop devices. The minors for the main loop devices will be
	 * multiples of max_part.
	 *
	 * Note: Global-for-all-devices, set-only-at-init, read-only module
	 * parameteters like 'max_loop' and 'max_part' make things needlessly
	 * complicated, are too static, inflexible and may surprise
	 * userspace tools. Parameters like this in general should be avoided.
	 */
	if (!part_shift)
		set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
	mutex_init(&lo->lo_mutex);
	lo->lo_number		= i;
	spin_lock_init(&lo->lo_lock);
	spin_lock_init(&lo->lo_work_lock);
	INIT_WORK(&lo->rootcg_work, loop_rootcg_workfn);
	INIT_LIST_HEAD(&lo->rootcg_cmd_list);
	disk->major		= LOOP_MAJOR;
	disk->first_minor	= i << part_shift;
	disk->minors		= 1 << part_shift;
	disk->fops		= &lo_fops;
	disk->private_data	= lo;
	disk->queue		= lo->lo_queue;
	disk->events		= DISK_EVENT_MEDIA_CHANGE;
	disk->event_flags	= DISK_EVENT_FLAG_UEVENT;
	sprintf(disk->disk_name, "loop%d", i);
	/* Make this loop device reachable from pathname. */
	err = add_disk(disk);
	if (err)
		goto out_cleanup_disk;

	/* Show this loop device. */
	mutex_lock(&loop_ctl_mutex);
	lo->idr_visible = true;
	mutex_unlock(&loop_ctl_mutex);

	return i;

out_cleanup_disk:
	put_disk(disk);
out_cleanup_tags:
	blk_mq_free_tag_set(&lo->tag_set);
out_free_idr:
	mutex_lock(&loop_ctl_mutex);
	idr_remove(&loop_index_idr, i);
	mutex_unlock(&loop_ctl_mutex);
out_free_dev:
	kfree(lo);
out:
	return err;
}

static void loop_remove(struct loop_device *lo)
{
	/* Make this loop device unreachable from pathname. */
	del_gendisk(lo->lo_disk);
	blk_mq_free_tag_set(&lo->tag_set);

	mutex_lock(&loop_ctl_mutex);
	idr_remove(&loop_index_idr, lo->lo_number);
	mutex_unlock(&loop_ctl_mutex);

	put_disk(lo->lo_disk);
}

#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
static void loop_probe(dev_t dev)
{
	int idx = MINOR(dev) >> part_shift;

	if (max_loop_specified && max_loop && idx >= max_loop)
		return;
	loop_add(idx);
}
#else
#define loop_probe NULL
#endif /* !CONFIG_BLOCK_LEGACY_AUTOLOAD */

static int loop_control_remove(int idx)
{
	struct loop_device *lo;
	int ret;

	if (idx < 0) {
		pr_warn_once("deleting an unspecified loop device is not supported.\n");
		return -EINVAL;
	}

	/* Hide this loop device for serialization. */
	ret = mutex_lock_killable(&loop_ctl_mutex);
	if (ret)
		return ret;
	lo = idr_find(&loop_index_idr, idx);
	if (!lo || !lo->idr_visible)
		ret = -ENODEV;
	else
		lo->idr_visible = false;
	mutex_unlock(&loop_ctl_mutex);
	if (ret)
		return ret;

	/* Check whether this loop device can be removed. */
	ret = mutex_lock_killable(&lo->lo_mutex);
	if (ret)
		goto mark_visible;
	if (lo->lo_state != Lo_unbound || disk_openers(lo->lo_disk) > 0) {
		mutex_unlock(&lo->lo_mutex);
		ret = -EBUSY;
		goto mark_visible;
	}
	/* Mark this loop device as no more bound, but not quite unbound yet */
	WRITE_ONCE(lo->lo_state, Lo_deleting);
	mutex_unlock(&lo->lo_mutex);

	loop_remove(lo);
	return 0;

mark_visible:
	/* Show this loop device again. */
	mutex_lock(&loop_ctl_mutex);
	lo->idr_visible = true;
	mutex_unlock(&loop_ctl_mutex);
	return ret;
}

static int loop_control_get_free(int idx)
{
	struct loop_device *lo;
	int id, ret;

	ret = mutex_lock_killable(&loop_ctl_mutex);
	if (ret)
		return ret;
	idr_for_each_entry(&loop_index_idr, lo, id) {
		/*
		 * Hitting a race results in creating a new loop device
		 * which is harmless.
		 */
		if (lo->idr_visible &&
		    data_race(READ_ONCE(lo->lo_state)) == Lo_unbound)
			goto found;
	}
	mutex_unlock(&loop_ctl_mutex);
	return loop_add(-1);
found:
	mutex_unlock(&loop_ctl_mutex);
	return id;
}

static long loop_control_ioctl(struct file *file, unsigned int cmd,
			       unsigned long parm)
{
	switch (cmd) {
	case LOOP_CTL_ADD:
		return loop_add(parm);
	case LOOP_CTL_REMOVE:
		return loop_control_remove(parm);
	case LOOP_CTL_GET_FREE:
		return loop_control_get_free(parm);
	default:
		return -ENOSYS;
	}
}

static const struct file_operations loop_ctl_fops = {
	.open		= nonseekable_open,
	.unlocked_ioctl	= loop_control_ioctl,
	.compat_ioctl	= loop_control_ioctl,
	.owner		= THIS_MODULE,
	.llseek		= noop_llseek,
};

static struct miscdevice loop_misc = {
	.minor		= LOOP_CTRL_MINOR,
	.name		= "loop-control",
	.fops		= &loop_ctl_fops,
};

MODULE_ALIAS_MISCDEV(LOOP_CTRL_MINOR);
MODULE_ALIAS("devname:loop-control");

static int __init loop_init(void)
{
	int i;
	int err;

	part_shift = 0;
	if (max_part > 0) {
		part_shift = fls(max_part);

		/*
		 * Adjust max_part according to part_shift as it is exported
		 * to user space so that user can decide correct minor number
		 * if [s]he want to create more devices.
		 *
		 * Note that -1 is required because partition 0 is reserved
		 * for the whole disk.
		 */
		max_part = (1UL << part_shift) - 1;
	}

	if ((1UL << part_shift) > DISK_MAX_PARTS) {
		err = -EINVAL;
		goto err_out;
	}

	if (max_loop > 1UL << (MINORBITS - part_shift)) {
		err = -EINVAL;
		goto err_out;
	}

	err = misc_register(&loop_misc);
	if (err < 0)
		goto err_out;


	if (__register_blkdev(LOOP_MAJOR, "loop", loop_probe)) {
		err = -EIO;
		goto misc_out;
	}

	/* pre-create number of devices given by config or max_loop */
	for (i = 0; i < max_loop; i++)
		loop_add(i);

	printk(KERN_INFO "loop: module loaded\n");
	return 0;

misc_out:
	misc_deregister(&loop_misc);
err_out:
	return err;
}

static void __exit loop_exit(void)
{
	struct loop_device *lo;
	int id;

	unregister_blkdev(LOOP_MAJOR, "loop");
	misc_deregister(&loop_misc);

	/*
	 * There is no need to use loop_ctl_mutex here, for nobody else can
	 * access loop_index_idr when this module is unloading (unless forced
	 * module unloading is requested). If this is not a clean unloading,
	 * we have no means to avoid kernel crash.
	 */
	idr_for_each_entry(&loop_index_idr, lo, id)
		loop_remove(lo);

	idr_destroy(&loop_index_idr);
}

module_init(loop_init);
module_exit(loop_exit);

#ifndef MODULE
static int __init max_loop_setup(char *str)
{
	max_loop = simple_strtol(str, NULL, 0);
#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
	max_loop_specified = true;
#endif
	return 1;
}

__setup("max_loop=", max_loop_setup);
#endif