block/bdev.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  Copyright (C) 2001  Andrea Arcangeli <andrea@suse.de> SuSE
 *  Copyright (C) 2016 - 2020 Christoph Hellwig
 */

#include <linux/init.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/kmod.h>
#include <linux/major.h>
#include <linux/device_cgroup.h>
#include <linux/blkdev.h>
#include <linux/blk-integrity.h>
#include <linux/backing-dev.h>
#include <linux/module.h>
#include <linux/blkpg.h>
#include <linux/magic.h>
#include <linux/buffer_head.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/mount.h>
#include <linux/pseudo_fs.h>
#include <linux/uio.h>
#include <linux/namei.h>
#include <linux/cleancache.h>
#include <linux/part_stat.h>
#include <linux/uaccess.h>
#include "../fs/internal.h"
#include "blk.h"

struct bdev_inode {
	struct block_device bdev;
	struct inode vfs_inode;
};

static inline struct bdev_inode *BDEV_I(struct inode *inode)
{
	return container_of(inode, struct bdev_inode, vfs_inode);
}

struct block_device *I_BDEV(struct inode *inode)
{
	return &BDEV_I(inode)->bdev;
}
EXPORT_SYMBOL(I_BDEV);

static void bdev_write_inode(struct block_device *bdev)
{
	struct inode *inode = bdev->bd_inode;
	int ret;

	spin_lock(&inode->i_lock);
	while (inode->i_state & I_DIRTY) {
		spin_unlock(&inode->i_lock);
		ret = write_inode_now(inode, true);
		if (ret) {
			char name[BDEVNAME_SIZE];
			pr_warn_ratelimited("VFS: Dirty inode writeback failed "
					    "for block device %s (err=%d).\n",
					    bdevname(bdev, name), ret);
		}
		spin_lock(&inode->i_lock);
	}
	spin_unlock(&inode->i_lock);
}

/* Kill _all_ buffers and pagecache , dirty or not.. */
static void kill_bdev(struct block_device *bdev)
{
	struct address_space *mapping = bdev->bd_inode->i_mapping;

	if (mapping_empty(mapping))
		return;

	invalidate_bh_lrus();
	truncate_inode_pages(mapping, 0);
}

/* Invalidate clean unused buffers and pagecache. */
void invalidate_bdev(struct block_device *bdev)
{
	struct address_space *mapping = bdev->bd_inode->i_mapping;

	if (mapping->nrpages) {
		invalidate_bh_lrus();
		lru_add_drain_all();	/* make sure all lru add caches are flushed */
		invalidate_mapping_pages(mapping, 0, -1);
	}
	/* 99% of the time, we don't need to flush the cleancache on the bdev.
	 * But, for the strange corners, lets be cautious
	 */
	cleancache_invalidate_inode(mapping);
}
EXPORT_SYMBOL(invalidate_bdev);

/*
 * Drop all buffers & page cache for given bdev range. This function bails
 * with error if bdev has other exclusive owner (such as filesystem).
 */
int truncate_bdev_range(struct block_device *bdev, fmode_t mode,
			loff_t lstart, loff_t lend)
{
	/*
	 * If we don't hold exclusive handle for the device, upgrade to it
	 * while we discard the buffer cache to avoid discarding buffers
	 * under live filesystem.
	 */
	if (!(mode & FMODE_EXCL)) {
		int err = bd_prepare_to_claim(bdev, truncate_bdev_range);
		if (err)
			goto invalidate;
	}

	truncate_inode_pages_range(bdev->bd_inode->i_mapping, lstart, lend);
	if (!(mode & FMODE_EXCL))
		bd_abort_claiming(bdev, truncate_bdev_range);
	return 0;

invalidate:
	/*
	 * Someone else has handle exclusively open. Try invalidating instead.
	 * The 'end' argument is inclusive so the rounding is safe.
	 */
	return invalidate_inode_pages2_range(bdev->bd_inode->i_mapping,
					     lstart >> PAGE_SHIFT,
					     lend >> PAGE_SHIFT);
}

static void set_init_blocksize(struct block_device *bdev)
{
	unsigned int bsize = bdev_logical_block_size(bdev);
	loff_t size = i_size_read(bdev->bd_inode);

	while (bsize < PAGE_SIZE) {
		if (size & bsize)
			break;
		bsize <<= 1;
	}
	bdev->bd_inode->i_blkbits = blksize_bits(bsize);
}

int set_blocksize(struct block_device *bdev, int size)
{
	/* Size must be a power of two, and between 512 and PAGE_SIZE */
	if (size > PAGE_SIZE || size < 512 || !is_power_of_2(size))
		return -EINVAL;

	/* Size cannot be smaller than the size supported by the device */
	if (size < bdev_logical_block_size(bdev))
		return -EINVAL;

	/* Don't change the size if it is same as current */
	if (bdev->bd_inode->i_blkbits != blksize_bits(size)) {
		sync_blockdev(bdev);
		bdev->bd_inode->i_blkbits = blksize_bits(size);
		kill_bdev(bdev);
	}
	return 0;
}

EXPORT_SYMBOL(set_blocksize);

int sb_set_blocksize(struct super_block *sb, int size)
{
	if (set_blocksize(sb->s_bdev, size))
		return 0;
	/* If we get here, we know size is power of two
	 * and it's value is between 512 and PAGE_SIZE */
	sb->s_blocksize = size;
	sb->s_blocksize_bits = blksize_bits(size);
	return sb->s_blocksize;
}

EXPORT_SYMBOL(sb_set_blocksize);

int sb_min_blocksize(struct super_block *sb, int size)
{
	int minsize = bdev_logical_block_size(sb->s_bdev);
	if (size < minsize)
		size = minsize;
	return sb_set_blocksize(sb, size);
}

EXPORT_SYMBOL(sb_min_blocksize);

int __sync_blockdev(struct block_device *bdev, int wait)
{
	if (!bdev)
		return 0;
	if (!wait)
		return filemap_flush(bdev->bd_inode->i_mapping);
	return filemap_write_and_wait(bdev->bd_inode->i_mapping);
}

/*
 * Write out and wait upon all the dirty data associated with a block
 * device via its mapping.  Does not take the superblock lock.
 */
int sync_blockdev(struct block_device *bdev)
{
	return __sync_blockdev(bdev, 1);
}
EXPORT_SYMBOL(sync_blockdev);

/*
 * Write out and wait upon all dirty data associated with this
 * device.   Filesystem data as well as the underlying block
 * device.  Takes the superblock lock.
 */
int fsync_bdev(struct block_device *bdev)
{
	struct super_block *sb = get_super(bdev);
	if (sb) {
		int res = sync_filesystem(sb);
		drop_super(sb);
		return res;
	}
	return sync_blockdev(bdev);
}
EXPORT_SYMBOL(fsync_bdev);

/**
 * freeze_bdev  --  lock a filesystem and force it into a consistent state
 * @bdev:	blockdevice to lock
 *
 * If a superblock is found on this device, we take the s_umount semaphore
 * on it to make sure nobody unmounts until the snapshot creation is done.
 * The reference counter (bd_fsfreeze_count) guarantees that only the last
 * unfreeze process can unfreeze the frozen filesystem actually when multiple
 * freeze requests arrive simultaneously. It counts up in freeze_bdev() and
 * count down in thaw_bdev(). When it becomes 0, thaw_bdev() will unfreeze
 * actually.
 */
int freeze_bdev(struct block_device *bdev)
{
	struct super_block *sb;
	int error = 0;

	mutex_lock(&bdev->bd_fsfreeze_mutex);
	if (++bdev->bd_fsfreeze_count > 1)
		goto done;

	sb = get_active_super(bdev);
	if (!sb)
		goto sync;
	if (sb->s_op->freeze_super)
		error = sb->s_op->freeze_super(sb);
	else
		error = freeze_super(sb);
	deactivate_super(sb);

	if (error) {
		bdev->bd_fsfreeze_count--;
		goto done;
	}
	bdev->bd_fsfreeze_sb = sb;

sync:
	sync_blockdev(bdev);
done:
	mutex_unlock(&bdev->bd_fsfreeze_mutex);
	return error;
}
EXPORT_SYMBOL(freeze_bdev);

/**
 * thaw_bdev  -- unlock filesystem
 * @bdev:	blockdevice to unlock
 *
 * Unlocks the filesystem and marks it writeable again after freeze_bdev().
 */
int thaw_bdev(struct block_device *bdev)
{
	struct super_block *sb;
	int error = -EINVAL;

	mutex_lock(&bdev->bd_fsfreeze_mutex);
	if (!bdev->bd_fsfreeze_count)
		goto out;

	error = 0;
	if (--bdev->bd_fsfreeze_count > 0)
		goto out;

	sb = bdev->bd_fsfreeze_sb;
	if (!sb)
		goto out;

	if (sb->s_op->thaw_super)
		error = sb->s_op->thaw_super(sb);
	else
		error = thaw_super(sb);
	if (error)
		bdev->bd_fsfreeze_count++;
	else
		bdev->bd_fsfreeze_sb = NULL;
out:
	mutex_unlock(&bdev->bd_fsfreeze_mutex);
	return error;
}
EXPORT_SYMBOL(thaw_bdev);

/**
 * bdev_read_page() - Start reading a page from a block device
 * @bdev: The device to read the page from
 * @sector: The offset on the device to read the page to (need not be aligned)
 * @page: The page to read
 *
 * On entry, the page should be locked.  It will be unlocked when the page
 * has been read.  If the block driver implements rw_page synchronously,
 * that will be true on exit from this function, but it need not be.
 *
 * Errors returned by this function are usually "soft", eg out of memory, or
 * queue full; callers should try a different route to read this page rather
 * than propagate an error back up the stack.
 *
 * Return: negative errno if an error occurs, 0 if submission was successful.
 */
int bdev_read_page(struct block_device *bdev, sector_t sector,
			struct page *page)
{
	const struct block_device_operations *ops = bdev->bd_disk->fops;
	int result = -EOPNOTSUPP;

	if (!ops->rw_page || bdev_get_integrity(bdev))
		return result;

	result = blk_queue_enter(bdev_get_queue(bdev), 0);
	if (result)
		return result;
	result = ops->rw_page(bdev, sector + get_start_sect(bdev), page,
			      REQ_OP_READ);
	blk_queue_exit(bdev_get_queue(bdev));
	return result;
}

/**
 * bdev_write_page() - Start writing a page to a block device
 * @bdev: The device to write the page to
 * @sector: The offset on the device to write the page to (need not be aligned)
 * @page: The page to write
 * @wbc: The writeback_control for the write
 *
 * On entry, the page should be locked and not currently under writeback.
 * On exit, if the write started successfully, the page will be unlocked and
 * under writeback.  If the write failed already (eg the driver failed to
 * queue the page to the device), the page will still be locked.  If the
 * caller is a ->writepage implementation, it will need to unlock the page.
 *
 * Errors returned by this function are usually "soft", eg out of memory, or
 * queue full; callers should try a different route to write this page rather
 * than propagate an error back up the stack.
 *
 * Return: negative errno if an error occurs, 0 if submission was successful.
 */
int bdev_write_page(struct block_device *bdev, sector_t sector,
			struct page *page, struct writeback_control *wbc)
{
	int result;
	const struct block_device_operations *ops = bdev->bd_disk->fops;

	if (!ops->rw_page || bdev_get_integrity(bdev))
		return -EOPNOTSUPP;
	result = blk_queue_enter(bdev_get_queue(bdev), 0);
	if (result)
		return result;

	set_page_writeback(page);
	result = ops->rw_page(bdev, sector + get_start_sect(bdev), page,
			      REQ_OP_WRITE);
	if (result) {
		end_page_writeback(page);
	} else {
		clean_page_buffers(page);
		unlock_page(page);
	}
	blk_queue_exit(bdev_get_queue(bdev));
	return result;
}

/*
 * pseudo-fs
 */

static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(bdev_lock);
static struct kmem_cache * bdev_cachep __read_mostly;

static struct inode *bdev_alloc_inode(struct super_block *sb)
{
	struct bdev_inode *ei = kmem_cache_alloc(bdev_cachep, GFP_KERNEL);

	if (!ei)
		return NULL;
	memset(&ei->bdev, 0, sizeof(ei->bdev));
	return &ei->vfs_inode;
}

static void bdev_free_inode(struct inode *inode)
{
	struct block_device *bdev = I_BDEV(inode);

	free_percpu(bdev->bd_stats);
	kfree(bdev->bd_meta_info);

	if (!bdev_is_partition(bdev)) {
		if (bdev->bd_disk && bdev->bd_disk->bdi)
			bdi_put(bdev->bd_disk->bdi);
		kfree(bdev->bd_disk);
	}

	if (MAJOR(bdev->bd_dev) == BLOCK_EXT_MAJOR)
		blk_free_ext_minor(MINOR(bdev->bd_dev));

	kmem_cache_free(bdev_cachep, BDEV_I(inode));
}

static void init_once(void *data)
{
	struct bdev_inode *ei = data;

	inode_init_once(&ei->vfs_inode);
}

static void bdev_evict_inode(struct inode *inode)
{
	truncate_inode_pages_final(&inode->i_data);
	invalidate_inode_buffers(inode); /* is it needed here? */
	clear_inode(inode);
}

static const struct super_operations bdev_sops = {
	.statfs = simple_statfs,
	.alloc_inode = bdev_alloc_inode,
	.free_inode = bdev_free_inode,
	.drop_inode = generic_delete_inode,
	.evict_inode = bdev_evict_inode,
};

static int bd_init_fs_context(struct fs_context *fc)
{
	struct pseudo_fs_context *ctx = init_pseudo(fc, BDEVFS_MAGIC);
	if (!ctx)
		return -ENOMEM;
	fc->s_iflags |= SB_I_CGROUPWB;
	ctx->ops = &bdev_sops;
	return 0;
}

static struct file_system_type bd_type = {
	.name		= "bdev",
	.init_fs_context = bd_init_fs_context,
	.kill_sb	= kill_anon_super,
};

struct super_block *blockdev_superblock __read_mostly;
EXPORT_SYMBOL_GPL(blockdev_superblock);

void __init bdev_cache_init(void)
{
	int err;
	static struct vfsmount *bd_mnt;

	bdev_cachep = kmem_cache_create("bdev_cache", sizeof(struct bdev_inode),
			0, (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
				SLAB_MEM_SPREAD|SLAB_ACCOUNT|SLAB_PANIC),
			init_once);
	err = register_filesystem(&bd_type);
	if (err)
		panic("Cannot register bdev pseudo-fs");
	bd_mnt = kern_mount(&bd_type);
	if (IS_ERR(bd_mnt))
		panic("Cannot create bdev pseudo-fs");
	blockdev_superblock = bd_mnt->mnt_sb;   /* For writeback */
}

struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
{
	struct block_device *bdev;
	struct inode *inode;

	inode = new_inode(blockdev_superblock);
	if (!inode)
		return NULL;
	inode->i_mode = S_IFBLK;
	inode->i_rdev = 0;
	inode->i_data.a_ops = &def_blk_aops;
	mapping_set_gfp_mask(&inode->i_data, GFP_USER);

	bdev = I_BDEV(inode);
	mutex_init(&bdev->bd_fsfreeze_mutex);
	spin_lock_init(&bdev->bd_size_lock);
	bdev->bd_partno = partno;
	bdev->bd_inode = inode;
	bdev->bd_queue = disk->queue;
	bdev->bd_stats = alloc_percpu(struct disk_stats);
	if (!bdev->bd_stats) {
		iput(inode);
		return NULL;
	}
	bdev->bd_disk = disk;
	return bdev;
}

void bdev_add(struct block_device *bdev, dev_t dev)
{
	bdev->bd_dev = dev;
	bdev->bd_inode->i_rdev = dev;
	bdev->bd_inode->i_ino = dev;
	insert_inode_hash(bdev->bd_inode);
}

long nr_blockdev_pages(void)
{
	struct inode *inode;
	long ret = 0;

	spin_lock(&blockdev_superblock->s_inode_list_lock);
	list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list)
		ret += inode->i_mapping->nrpages;
	spin_unlock(&blockdev_superblock->s_inode_list_lock);

	return ret;
}

/**
 * bd_may_claim - test whether a block device can be claimed
 * @bdev: block device of interest
 * @whole: whole block device containing @bdev, may equal @bdev
 * @holder: holder trying to claim @bdev
 *
 * Test whether @bdev can be claimed by @holder.
 *
 * CONTEXT:
 * spin_lock(&bdev_lock).
 *
 * RETURNS:
 * %true if @bdev can be claimed, %false otherwise.
 */
static bool bd_may_claim(struct block_device *bdev, struct block_device *whole,
			 void *holder)
{
	if (bdev->bd_holder == holder)
		return true;	 /* already a holder */
	else if (bdev->bd_holder != NULL)
		return false; 	 /* held by someone else */
	else if (whole == bdev)
		return true;  	 /* is a whole device which isn't held */

	else if (whole->bd_holder == bd_may_claim)
		return true; 	 /* is a partition of a device that is being partitioned */
	else if (whole->bd_holder != NULL)
		return false;	 /* is a partition of a held device */
	else
		return true;	 /* is a partition of an un-held device */
}

/**
 * bd_prepare_to_claim - claim a block device
 * @bdev: block device of interest
 * @holder: holder trying to claim @bdev
 *
 * Claim @bdev.  This function fails if @bdev is already claimed by another
 * holder and waits if another claiming is in progress. return, the caller
 * has ownership of bd_claiming and bd_holder[s].
 *
 * RETURNS:
 * 0 if @bdev can be claimed, -EBUSY otherwise.
 */
int bd_prepare_to_claim(struct block_device *bdev, void *holder)
{
	struct block_device *whole = bdev_whole(bdev);

	if (WARN_ON_ONCE(!holder))
		return -EINVAL;
retry:
	spin_lock(&bdev_lock);
	/* if someone else claimed, fail */
	if (!bd_may_claim(bdev, whole, holder)) {
		spin_unlock(&bdev_lock);
		return -EBUSY;
	}

	/* if claiming is already in progress, wait for it to finish */
	if (whole->bd_claiming) {
		wait_queue_head_t *wq = bit_waitqueue(&whole->bd_claiming, 0);
		DEFINE_WAIT(wait);

		prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
		spin_unlock(&bdev_lock);
		schedule();
		finish_wait(wq, &wait);
		goto retry;
	}

	/* yay, all mine */
	whole->bd_claiming = holder;
	spin_unlock(&bdev_lock);
	return 0;
}
EXPORT_SYMBOL_GPL(bd_prepare_to_claim); /* only for the loop driver */

static void bd_clear_claiming(struct block_device *whole, void *holder)
{
	lockdep_assert_held(&bdev_lock);
	/* tell others that we're done */
	BUG_ON(whole->bd_claiming != holder);
	whole->bd_claiming = NULL;
	wake_up_bit(&whole->bd_claiming, 0);
}

/**
 * bd_finish_claiming - finish claiming of a block device
 * @bdev: block device of interest
 * @holder: holder that has claimed @bdev
 *
 * Finish exclusive open of a block device. Mark the device as exlusively
 * open by the holder and wake up all waiters for exclusive open to finish.
 */
static void bd_finish_claiming(struct block_device *bdev, void *holder)
{
	struct block_device *whole = bdev_whole(bdev);

	spin_lock(&bdev_lock);
	BUG_ON(!bd_may_claim(bdev, whole, holder));
	/*
	 * Note that for a whole device bd_holders will be incremented twice,
	 * and bd_holder will be set to bd_may_claim before being set to holder
	 */
	whole->bd_holders++;
	whole->bd_holder = bd_may_claim;
	bdev->bd_holders++;
	bdev->bd_holder = holder;
	bd_clear_claiming(whole, holder);
	spin_unlock(&bdev_lock);
}

/**
 * bd_abort_claiming - abort claiming of a block device
 * @bdev: block device of interest
 * @holder: holder that has claimed @bdev
 *
 * Abort claiming of a block device when the exclusive open failed. This can be
 * also used when exclusive open is not actually desired and we just needed
 * to block other exclusive openers for a while.
 */
void bd_abort_claiming(struct block_device *bdev, void *holder)
{
	spin_lock(&bdev_lock);
	bd_clear_claiming(bdev_whole(bdev), holder);
	spin_unlock(&bdev_lock);
}
EXPORT_SYMBOL(bd_abort_claiming);

static void blkdev_flush_mapping(struct block_device *bdev)
{
	WARN_ON_ONCE(bdev->bd_holders);
	sync_blockdev(bdev);
	kill_bdev(bdev);
	bdev_write_inode(bdev);
}

static int blkdev_get_whole(struct block_device *bdev, fmode_t mode)
{
	struct gendisk *disk = bdev->bd_disk;
	int ret = 0;

	if (disk->fops->open) {
		ret = disk->fops->open(bdev, mode);
		if (ret) {
			/* avoid ghost partitions on a removed medium */
			if (ret == -ENOMEDIUM &&
			     test_bit(GD_NEED_PART_SCAN, &disk->state))
				bdev_disk_changed(disk, true);
			return ret;
		}
	}

	if (!bdev->bd_openers)
		set_init_blocksize(bdev);
	if (test_bit(GD_NEED_PART_SCAN, &disk->state))
		bdev_disk_changed(disk, false);
	bdev->bd_openers++;
	return 0;;
}

static void blkdev_put_whole(struct block_device *bdev, fmode_t mode)
{
	if (!--bdev->bd_openers)
		blkdev_flush_mapping(bdev);
	if (bdev->bd_disk->fops->release)
		bdev->bd_disk->fops->release(bdev->bd_disk, mode);
}

static int blkdev_get_part(struct block_device *part, fmode_t mode)
{
	struct gendisk *disk = part->bd_disk;
	int ret;

	if (part->bd_openers)
		goto done;

	ret = blkdev_get_whole(bdev_whole(part), mode);
	if (ret)
		return ret;

	ret = -ENXIO;
	if (!bdev_nr_sectors(part))
		goto out_blkdev_put;

	disk->open_partitions++;
	set_init_blocksize(part);
done:
	part->bd_openers++;
	return 0;

out_blkdev_put:
	blkdev_put_whole(bdev_whole(part), mode);
	return ret;
}

static void blkdev_put_part(struct block_device *part, fmode_t mode)
{
	struct block_device *whole = bdev_whole(part);

	if (--part->bd_openers)
		return;
	blkdev_flush_mapping(part);
	whole->bd_disk->open_partitions--;
	blkdev_put_whole(whole, mode);
}

struct block_device *blkdev_get_no_open(dev_t dev)
{
	struct block_device *bdev;
	struct inode *inode;

	inode = ilookup(blockdev_superblock, dev);
	if (!inode) {
		blk_request_module(dev);
		inode = ilookup(blockdev_superblock, dev);
		if (!inode)
			return NULL;
	}

	/* switch from the inode reference to a device mode one: */
	bdev = &BDEV_I(inode)->bdev;
	if (!kobject_get_unless_zero(&bdev->bd_device.kobj))
		bdev = NULL;
	iput(inode);

	if (!bdev)
		return NULL;
	if ((bdev->bd_disk->flags & GENHD_FL_HIDDEN) ||
	    !try_module_get(bdev->bd_disk->fops->owner)) {
		put_device(&bdev->bd_device);
		return NULL;
	}

	return bdev;
}

void blkdev_put_no_open(struct block_device *bdev)
{
	module_put(bdev->bd_disk->fops->owner);
	put_device(&bdev->bd_device);
}

/**
 * blkdev_get_by_dev - open a block device by device number
 * @dev: device number of block device to open
 * @mode: FMODE_* mask
 * @holder: exclusive holder identifier
 *
 * Open the block device described by device number @dev. If @mode includes
 * %FMODE_EXCL, the block device is opened with exclusive access.  Specifying
 * %FMODE_EXCL with a %NULL @holder is invalid.  Exclusive opens may nest for
 * the same @holder.
 *
 * Use this interface ONLY if you really do not have anything better - i.e. when
 * you are behind a truly sucky interface and all you are given is a device
 * number.  Everything else should use blkdev_get_by_path().
 *
 * CONTEXT:
 * Might sleep.
 *
 * RETURNS:
 * Reference to the block_device on success, ERR_PTR(-errno) on failure.
 */
struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
{
	bool unblock_events = true;
	struct block_device *bdev;
	struct gendisk *disk;
	int ret;

	ret = devcgroup_check_permission(DEVCG_DEV_BLOCK,
			MAJOR(dev), MINOR(dev),
			((mode & FMODE_READ) ? DEVCG_ACC_READ : 0) |
			((mode & FMODE_WRITE) ? DEVCG_ACC_WRITE : 0));
	if (ret)
		return ERR_PTR(ret);

	bdev = blkdev_get_no_open(dev);
	if (!bdev)
		return ERR_PTR(-ENXIO);
	disk = bdev->bd_disk;

	if (mode & FMODE_EXCL) {
		ret = bd_prepare_to_claim(bdev, holder);
		if (ret)
			goto put_blkdev;
	}

	disk_block_events(disk);

	mutex_lock(&disk->open_mutex);
	ret = -ENXIO;
	if (!disk_live(disk))
		goto abort_claiming;
	if (bdev_is_partition(bdev))
		ret = blkdev_get_part(bdev, mode);
	else
		ret = blkdev_get_whole(bdev, mode);
	if (ret)
		goto abort_claiming;
	if (mode & FMODE_EXCL) {
		bd_finish_claiming(bdev, holder);

		/*
		 * Block event polling for write claims if requested.  Any write
		 * holder makes the write_holder state stick until all are
		 * released.  This is good enough and tracking individual
		 * writeable reference is too fragile given the way @mode is
		 * used in blkdev_get/put().
		 */
		if ((mode & FMODE_WRITE) && !bdev->bd_write_holder &&
		    (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
			bdev->bd_write_holder = true;
			unblock_events = false;
		}
	}
	mutex_unlock(&disk->open_mutex);

	if (unblock_events)
		disk_unblock_events(disk);
	return bdev;

abort_claiming:
	if (mode & FMODE_EXCL)
		bd_abort_claiming(bdev, holder);
	mutex_unlock(&disk->open_mutex);
	disk_unblock_events(disk);
put_blkdev:
	blkdev_put_no_open(bdev);
	return ERR_PTR(ret);
}
EXPORT_SYMBOL(blkdev_get_by_dev);

/**
 * blkdev_get_by_path - open a block device by name
 * @path: path to the block device to open
 * @mode: FMODE_* mask
 * @holder: exclusive holder identifier
 *
 * Open the block device described by the device file at @path.  If @mode
 * includes %FMODE_EXCL, the block device is opened with exclusive access.
 * Specifying %FMODE_EXCL with a %NULL @holder is invalid.  Exclusive opens may
 * nest for the same @holder.
 *
 * CONTEXT:
 * Might sleep.
 *
 * RETURNS:
 * Reference to the block_device on success, ERR_PTR(-errno) on failure.
 */
struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
					void *holder)
{
	struct block_device *bdev;
	dev_t dev;
	int error;

	error = lookup_bdev(path, &dev);
	if (error)
		return ERR_PTR(error);

	bdev = blkdev_get_by_dev(dev, mode, holder);
	if (!IS_ERR(bdev) && (mode & FMODE_WRITE) && bdev_read_only(bdev)) {
		blkdev_put(bdev, mode);
		return ERR_PTR(-EACCES);
	}

	return bdev;
}
EXPORT_SYMBOL(blkdev_get_by_path);

void blkdev_put(struct block_device *bdev, fmode_t mode)
{
	struct gendisk *disk = bdev->bd_disk;

	/*
	 * Sync early if it looks like we're the last one.  If someone else
	 * opens the block device between now and the decrement of bd_openers
	 * then we did a sync that we didn't need to, but that's not the end
	 * of the world and we want to avoid long (could be several minute)
	 * syncs while holding the mutex.
	 */
	if (bdev->bd_openers == 1)
		sync_blockdev(bdev);

	mutex_lock(&disk->open_mutex);
	if (mode & FMODE_EXCL) {
		struct block_device *whole = bdev_whole(bdev);
		bool bdev_free;

		/*
		 * Release a claim on the device.  The holder fields
		 * are protected with bdev_lock.  open_mutex is to
		 * synchronize disk_holder unlinking.
		 */
		spin_lock(&bdev_lock);

		WARN_ON_ONCE(--bdev->bd_holders < 0);
		WARN_ON_ONCE(--whole->bd_holders < 0);

		if ((bdev_free = !bdev->bd_holders))
			bdev->bd_holder = NULL;
		if (!whole->bd_holders)
			whole->bd_holder = NULL;

		spin_unlock(&bdev_lock);

		/*
		 * If this was the last claim, remove holder link and
		 * unblock evpoll if it was a write holder.
		 */
		if (bdev_free && bdev->bd_write_holder) {
			disk_unblock_events(disk);
			bdev->bd_write_holder = false;
		}
	}

	/*
	 * Trigger event checking and tell drivers to flush MEDIA_CHANGE
	 * event.  This is to ensure detection of media removal commanded
	 * from userland - e.g. eject(1).
	 */
	disk_flush_events(disk, DISK_EVENT_MEDIA_CHANGE);

	if (bdev_is_partition(bdev))
		blkdev_put_part(bdev, mode);
	else
		blkdev_put_whole(bdev, mode);
	mutex_unlock(&disk->open_mutex);

	blkdev_put_no_open(bdev);
}
EXPORT_SYMBOL(blkdev_put);

/**
 * lookup_bdev  - lookup a struct block_device by name
 * @pathname:	special file representing the block device
 * @dev:	return value of the block device's dev_t
 *
 * Lookup the block device's dev_t at @pathname in the current
 * namespace if possible and return it by @dev.
 *
 * RETURNS:
 * 0 if succeeded, errno otherwise.
 */
int lookup_bdev(const char *pathname, dev_t *dev)
{
	struct inode *inode;
	struct path path;
	int error;

	if (!pathname || !*pathname)
		return -EINVAL;

	error = kern_path(pathname, LOOKUP_FOLLOW, &path);
	if (error)
		return error;

	inode = d_backing_inode(path.dentry);
	error = -ENOTBLK;
	if (!S_ISBLK(inode->i_mode))
		goto out_path_put;
	error = -EACCES;
	if (!may_open_dev(&path))
		goto out_path_put;

	*dev = inode->i_rdev;
	error = 0;
out_path_put:
	path_put(&path);
	return error;
}
EXPORT_SYMBOL(lookup_bdev);

int __invalidate_device(struct block_device *bdev, bool kill_dirty)
{
	struct super_block *sb = get_super(bdev);
	int res = 0;

	if (sb) {
		/*
		 * no need to lock the super, get_super holds the
		 * read mutex so the filesystem cannot go away
		 * under us (->put_super runs with the write lock
		 * hold).
		 */
		shrink_dcache_sb(sb);
		res = invalidate_inodes(sb, kill_dirty);
		drop_super(sb);
	}
	invalidate_bdev(bdev);
	return res;
}
EXPORT_SYMBOL(__invalidate_device);

void iterate_bdevs(void (*func)(struct block_device *, void *), void *arg)
{
	struct inode *inode, *old_inode = NULL;

	spin_lock(&blockdev_superblock->s_inode_list_lock);
	list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list) {
		struct address_space *mapping = inode->i_mapping;
		struct block_device *bdev;

		spin_lock(&inode->i_lock);
		if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW) ||
		    mapping->nrpages == 0) {
			spin_unlock(&inode->i_lock);
			continue;
		}
		__iget(inode);
		spin_unlock(&inode->i_lock);
		spin_unlock(&blockdev_superblock->s_inode_list_lock);
		/*
		 * We hold a reference to 'inode' so it couldn't have been
		 * removed from s_inodes list while we dropped the
		 * s_inode_list_lock  We cannot iput the inode now as we can
		 * be holding the last reference and we cannot iput it under
		 * s_inode_list_lock. So we keep the reference and iput it
		 * later.
		 */
		iput(old_inode);
		old_inode = inode;
		bdev = I_BDEV(inode);

		mutex_lock(&bdev->bd_disk->open_mutex);
		if (bdev->bd_openers)
			func(bdev, arg);
		mutex_unlock(&bdev->bd_disk->open_mutex);

		spin_lock(&blockdev_superblock->s_inode_list_lock);
	}
	spin_unlock(&blockdev_superblock->s_inode_list_lock);
	iput(old_inode);
}