// SPDX-License-Identifier: GPL-2.0-only

  /*
   *  linux/fs/block_dev.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   *  Copyright (C) 2001  Andrea Arcangeli <andrea@suse.de> SuSE
   */

  #include <linux/init.h>
  #include <linux/mm.h>
  #include <linux/fcntl.h>
  #include <linux/slab.h>
  #include <linux/kmod.h>
  #include <linux/major.h>

  #include <linux/device_cgroup.h>

  #include <linux/highmem.h>
  #include <linux/blkdev.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/pagevec.h>

  #include <linux/writeback.h>

  #include <linux/mpage.h>
  #include <linux/mount.h>

  #include <linux/pseudo_fs.h>

  #include <linux/uio.h>
  #include <linux/namei.h>

  #include <linux/log2.h>

  #include <linux/cleancache.h>

  #include <linux/task_io_accounting_ops.h>

  #include <linux/falloc.h>

  #include <linux/uaccess.h>

  #include <linux/suspend.h>

  #include "internal.h"

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

  static const struct address_space_operations def_blk_aops;

  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).
  ",
  					    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->nrpages == 0 && mapping->nrexceptional == 0)

  		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)
  {
  	struct block_device *claimed_bdev = NULL;
  	int err;
  
  	/*
  	 * 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)) {
  		claimed_bdev = bdev->bd_contains;
  		err = bd_prepare_to_claim(bdev, claimed_bdev,
  					  truncate_bdev_range);
  		if (err)
  			return err;
  	}
  	truncate_inode_pages_range(bdev->bd_inode->i_mapping, lstart, lend);
  	if (claimed_bdev)
  		bd_abort_claiming(bdev, claimed_bdev, truncate_bdev_range);
  	return 0;
  }
  EXPORT_SYMBOL(truncate_bdev_range);

  static void set_init_blocksize(struct block_device *bdev)
  {

  	bdev->bd_inode->i_blkbits = blksize_bits(bdev_logical_block_size(bdev));

  }

  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);
  
  static int
  blkdev_get_block(struct inode *inode, sector_t iblock,
  		struct buffer_head *bh, int create)
  {

  	bh->b_bdev = I_BDEV(inode);
  	bh->b_blocknr = iblock;
  	set_buffer_mapped(bh);
  	return 0;
  }

  static struct inode *bdev_file_inode(struct file *file)
  {
  	return file->f_mapping->host;
  }

  static unsigned int dio_bio_write_op(struct kiocb *iocb)
  {
  	unsigned int op = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
  
  	/* avoid the need for a I/O completion work item */
  	if (iocb->ki_flags & IOCB_DSYNC)
  		op |= REQ_FUA;
  	return op;
  }

  #define DIO_INLINE_BIO_VECS 4
  
  static void blkdev_bio_end_io_simple(struct bio *bio)
  {
  	struct task_struct *waiter = bio->bi_private;
  
  	WRITE_ONCE(bio->bi_private, NULL);

  	blk_wake_io_task(waiter);

  }
  
  static ssize_t
  __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
  		int nr_pages)
  {
  	struct file *file = iocb->ki_filp;
  	struct block_device *bdev = I_BDEV(bdev_file_inode(file));

  	struct bio_vec inline_vecs[DIO_INLINE_BIO_VECS], *vecs;

  	loff_t pos = iocb->ki_pos;
  	bool should_dirty = false;
  	struct bio bio;
  	ssize_t ret;
  	blk_qc_t qc;

  	if ((pos | iov_iter_alignment(iter)) &
  	    (bdev_logical_block_size(bdev) - 1))

  		return -EINVAL;

  	if (nr_pages <= DIO_INLINE_BIO_VECS)
  		vecs = inline_vecs;
  	else {

  		vecs = kmalloc_array(nr_pages, sizeof(struct bio_vec),
  				     GFP_KERNEL);

  		if (!vecs)
  			return -ENOMEM;
  	}

  	bio_init(&bio, vecs, nr_pages);

  	bio_set_dev(&bio, bdev);

  	bio.bi_iter.bi_sector = pos >> 9;

  	bio.bi_write_hint = iocb->ki_hint;

  	bio.bi_private = current;
  	bio.bi_end_io = blkdev_bio_end_io_simple;

  	bio.bi_ioprio = iocb->ki_ioprio;

  
  	ret = bio_iov_iter_get_pages(&bio, iter);
  	if (unlikely(ret))

  		goto out;

  	ret = bio.bi_iter.bi_size;
  
  	if (iov_iter_rw(iter) == READ) {

  		bio.bi_opf = REQ_OP_READ;

  		if (iter_is_iovec(iter))
  			should_dirty = true;
  	} else {

  		bio.bi_opf = dio_bio_write_op(iocb);

  		task_io_account_write(ret);
  	}

  	if (iocb->ki_flags & IOCB_HIPRI)

  		bio_set_polled(&bio, iocb);

  
  	qc = submit_bio(&bio);
  	for (;;) {

  		set_current_state(TASK_UNINTERRUPTIBLE);

  		if (!READ_ONCE(bio.bi_private))
  			break;
  		if (!(iocb->ki_flags & IOCB_HIPRI) ||

  		    !blk_poll(bdev_get_queue(bdev), qc, true))

  			blk_io_schedule();

  	}
  	__set_current_state(TASK_RUNNING);

  	bio_release_pages(&bio, should_dirty);

  	if (unlikely(bio.bi_status))

  		ret = blk_status_to_errno(bio.bi_status);

  out:
  	if (vecs != inline_vecs)
  		kfree(vecs);

  	bio_uninit(&bio);

  	return ret;
  }

  struct blkdev_dio {
  	union {
  		struct kiocb		*iocb;
  		struct task_struct	*waiter;
  	};
  	size_t			size;
  	atomic_t		ref;
  	bool			multi_bio : 1;
  	bool			should_dirty : 1;
  	bool			is_sync : 1;
  	struct bio		bio;
  };

  static struct bio_set blkdev_dio_pool;

  static int blkdev_iopoll(struct kiocb *kiocb, bool wait)
  {
  	struct block_device *bdev = I_BDEV(kiocb->ki_filp->f_mapping->host);
  	struct request_queue *q = bdev_get_queue(bdev);
  
  	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), wait);
  }

  static void blkdev_bio_end_io(struct bio *bio)
  {
  	struct blkdev_dio *dio = bio->bi_private;
  	bool should_dirty = dio->should_dirty;

  	if (bio->bi_status && !dio->bio.bi_status)
  		dio->bio.bi_status = bio->bi_status;
  
  	if (!dio->multi_bio || atomic_dec_and_test(&dio->ref)) {

  		if (!dio->is_sync) {
  			struct kiocb *iocb = dio->iocb;

  			ssize_t ret;

  			if (likely(!dio->bio.bi_status)) {

  				ret = dio->size;
  				iocb->ki_pos += ret;

  			} else {
  				ret = blk_status_to_errno(dio->bio.bi_status);

  			}
  
  			dio->iocb->ki_complete(iocb, ret, 0);

  			if (dio->multi_bio)
  				bio_put(&dio->bio);

  		} else {
  			struct task_struct *waiter = dio->waiter;
  
  			WRITE_ONCE(dio->waiter, NULL);

  			blk_wake_io_task(waiter);

  		}
  	}
  
  	if (should_dirty) {
  		bio_check_pages_dirty(bio);
  	} else {

  		bio_release_pages(bio, false);

  		bio_put(bio);
  	}
  }

  static ssize_t

  __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)

  {
  	struct file *file = iocb->ki_filp;

  	struct inode *inode = bdev_file_inode(file);

  	struct block_device *bdev = I_BDEV(inode);

  	struct blk_plug plug;

  	struct blkdev_dio *dio;
  	struct bio *bio;

  	bool is_poll = (iocb->ki_flags & IOCB_HIPRI) != 0;

  	bool is_read = (iov_iter_rw(iter) == READ), is_sync;

  	loff_t pos = iocb->ki_pos;
  	blk_qc_t qc = BLK_QC_T_NONE;

  	int ret = 0;

  	if ((pos | iov_iter_alignment(iter)) &
  	    (bdev_logical_block_size(bdev) - 1))

  		return -EINVAL;

  	bio = bio_alloc_bioset(GFP_KERNEL, nr_pages, &blkdev_dio_pool);

  
  	dio = container_of(bio, struct blkdev_dio, bio);

  	dio->is_sync = is_sync = is_sync_kiocb(iocb);

  	if (dio->is_sync) {

  		dio->waiter = current;

  		bio_get(bio);
  	} else {

  		dio->iocb = iocb;

  	}

  
  	dio->size = 0;
  	dio->multi_bio = false;

  	dio->should_dirty = is_read && iter_is_iovec(iter);

  	/*
  	 * Don't plug for HIPRI/polled IO, as those should go straight
  	 * to issue
  	 */
  	if (!is_poll)
  		blk_start_plug(&plug);

  	for (;;) {

  		bio_set_dev(bio, bdev);

  		bio->bi_iter.bi_sector = pos >> 9;

  		bio->bi_write_hint = iocb->ki_hint;

  		bio->bi_private = dio;
  		bio->bi_end_io = blkdev_bio_end_io;

  		bio->bi_ioprio = iocb->ki_ioprio;

  		ret = bio_iov_iter_get_pages(bio, iter);
  		if (unlikely(ret)) {

  			bio->bi_status = BLK_STS_IOERR;

  			bio_endio(bio);
  			break;
  		}
  
  		if (is_read) {
  			bio->bi_opf = REQ_OP_READ;
  			if (dio->should_dirty)
  				bio_set_pages_dirty(bio);
  		} else {
  			bio->bi_opf = dio_bio_write_op(iocb);
  			task_io_account_write(bio->bi_iter.bi_size);
  		}

  		dio->size += bio->bi_iter.bi_size;

  		pos += bio->bi_iter.bi_size;
  
  		nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
  		if (!nr_pages) {

  			bool polled = false;
  
  			if (iocb->ki_flags & IOCB_HIPRI) {

  				bio_set_polled(bio, iocb);

  				polled = true;
  			}

  			qc = submit_bio(bio);

  
  			if (polled)
  				WRITE_ONCE(iocb->ki_cookie, qc);

  			break;
  		}
  
  		if (!dio->multi_bio) {

  			/*
  			 * AIO needs an extra reference to ensure the dio
  			 * structure which is embedded into the first bio
  			 * stays around.
  			 */
  			if (!is_sync)
  				bio_get(bio);

  			dio->multi_bio = true;
  			atomic_set(&dio->ref, 2);
  		} else {
  			atomic_inc(&dio->ref);
  		}

  		submit_bio(bio);
  		bio = bio_alloc(GFP_KERNEL, nr_pages);

  	}

  
  	if (!is_poll)
  		blk_finish_plug(&plug);

  	if (!is_sync)

  		return -EIOCBQUEUED;
  
  	for (;;) {

  		set_current_state(TASK_UNINTERRUPTIBLE);

  		if (!READ_ONCE(dio->waiter))
  			break;
  
  		if (!(iocb->ki_flags & IOCB_HIPRI) ||

  		    !blk_poll(bdev_get_queue(bdev), qc, true))

  			blk_io_schedule();

  	}
  	__set_current_state(TASK_RUNNING);

  	if (!ret)

  		ret = blk_status_to_errno(dio->bio.bi_status);

  	if (likely(!ret))
  		ret = dio->size;

  
  	bio_put(&dio->bio);
  	return ret;
  }
  
  static ssize_t
  blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
  {

  	int nr_pages;

  	nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES + 1);

  	if (!nr_pages)
  		return 0;

  	if (is_sync_kiocb(iocb) && nr_pages <= BIO_MAX_PAGES)

  		return __blkdev_direct_IO_simple(iocb, iter, nr_pages);

  
  	return __blkdev_direct_IO(iocb, iter, min(nr_pages, BIO_MAX_PAGES));
  }
  
  static __init int blkdev_init(void)
  {

  	return bioset_init(&blkdev_dio_pool, 4, offsetof(struct blkdev_dio, bio), BIOSET_NEED_BVECS);

  }

  module_init(blkdev_init);

  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.
   */
  struct super_block *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) {
  		/*
  		 * We don't even need to grab a reference - the first call
  		 * to freeze_bdev grab an active reference and only the last
  		 * thaw_bdev drops it.
  		 */

  		sb = get_super(bdev);

  		if (sb)
  			drop_super(sb);

  		mutex_unlock(&bdev->bd_fsfreeze_mutex);
  		return sb;
  	}
  
  	sb = get_active_super(bdev);
  	if (!sb)
  		goto out;

  	if (sb->s_op->freeze_super)
  		error = sb->s_op->freeze_super(sb);
  	else
  		error = freeze_super(sb);

  	if (error) {
  		deactivate_super(sb);
  		bdev->bd_fsfreeze_count--;

  		mutex_unlock(&bdev->bd_fsfreeze_mutex);

  		return ERR_PTR(error);

  	}

  	deactivate_super(sb);

   out:

  	sync_blockdev(bdev);
  	mutex_unlock(&bdev->bd_fsfreeze_mutex);

  	return sb;	/* thaw_bdev releases s->s_umount */

  }
  EXPORT_SYMBOL(freeze_bdev);
  
  /**
   * thaw_bdev  -- unlock filesystem
   * @bdev:	blockdevice to unlock
   * @sb:		associated superblock
   *
   * 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;

  
  	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++;

  out:

  	mutex_unlock(&bdev->bd_fsfreeze_mutex);

  	return error;

  }
  EXPORT_SYMBOL(thaw_bdev);

  static int blkdev_writepage(struct page *page, struct writeback_control *wbc)
  {
  	return block_write_full_page(page, blkdev_get_block, wbc);
  }
  
  static int blkdev_readpage(struct file * file, struct page * page)
  {
  	return block_read_full_page(page, blkdev_get_block);
  }

  static void blkdev_readahead(struct readahead_control *rac)

  {

  	mpage_readahead(rac, blkdev_get_block);

  }

  static int blkdev_write_begin(struct file *file, struct address_space *mapping,
  			loff_t pos, unsigned len, unsigned flags,
  			struct page **pagep, void **fsdata)

  {

  	return block_write_begin(mapping, pos, len, flags, pagep,
  				 blkdev_get_block);

  }

  static int blkdev_write_end(struct file *file, struct address_space *mapping,
  			loff_t pos, unsigned len, unsigned copied,
  			struct page *page, void *fsdata)

  {

  	int ret;
  	ret = block_write_end(file, mapping, pos, len, copied, page, fsdata);
  
  	unlock_page(page);

  	put_page(page);

  
  	return ret;

  }
  
  /*
   * private llseek:

   * for a block special file file_inode(file)->i_size is zero

   * so we compute the size by hand (just as in block_read/write above)
   */

  static loff_t block_llseek(struct file *file, loff_t offset, int whence)

  {

  	struct inode *bd_inode = bdev_file_inode(file);

  	loff_t retval;

  	inode_lock(bd_inode);

  	retval = fixed_size_llseek(file, offset, whence, i_size_read(bd_inode));

  	inode_unlock(bd_inode);

  	return retval;
  }
  	

  int blkdev_fsync(struct file *filp, loff_t start, loff_t end, int datasync)

  {

  	struct inode *bd_inode = bdev_file_inode(filp);

  	struct block_device *bdev = I_BDEV(bd_inode);

  	int error;

  	error = file_write_and_wait_range(filp, start, end);

  	if (error)
  		return error;

  	/*
  	 * There is no need to serialise calls to blkdev_issue_flush with
  	 * i_mutex and doing so causes performance issues with concurrent
  	 * O_SYNC writers to a block device.
  	 */

  	error = blkdev_issue_flush(bdev, GFP_KERNEL);

  	if (error == -EOPNOTSUPP)
  		error = 0;

  	return error;

  }

  EXPORT_SYMBOL(blkdev_fsync);

  /**
   * 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->bd_disk->queue, 0);

  	if (result)
  		return result;

  	result = ops->rw_page(bdev, sector + get_start_sect(bdev), page,
  			      REQ_OP_READ);

  	blk_queue_exit(bdev->bd_disk->queue);

  	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->bd_disk->queue, 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->bd_disk->queue);

  	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;
  	return &ei->vfs_inode;
  }

  static void bdev_free_inode(struct inode *inode)

  {

  	kmem_cache_free(bdev_cachep, BDEV_I(inode));

  }

  static void init_once(void *foo)

  {
  	struct bdev_inode *ei = (struct bdev_inode *) foo;
  	struct block_device *bdev = &ei->bdev;

  	memset(bdev, 0, sizeof(*bdev));
  	mutex_init(&bdev->bd_mutex);

  #ifdef CONFIG_SYSFS
  	INIT_LIST_HEAD(&bdev->bd_holder_disks);
  #endif

  	bdev->bd_bdi = &noop_backing_dev_info;

  	inode_init_once(&ei->vfs_inode);

  	/* Initialize mutex for freeze. */
  	mutex_init(&bdev->bd_fsfreeze_mutex);

  }

  static void bdev_evict_inode(struct inode *inode)

  {
  	struct block_device *bdev = &BDEV_I(inode)->bdev;

  	truncate_inode_pages_final(&inode->i_data);

  	invalidate_inode_buffers(inode); /* is it needed here? */

  	clear_inode(inode);

  	/* Detach inode from wb early as bdi_put() may free bdi->wb */
  	inode_detach_wb(inode);

  	if (bdev->bd_bdi != &noop_backing_dev_info) {

  		bdi_put(bdev->bd_bdi);

  		bdev->bd_bdi = &noop_backing_dev_info;
  	}

  }

  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 */

  }
  
  /*
   * Most likely _very_ bad one - but then it's hardly critical for small
   * /dev and can be fixed when somebody will need really large one.
   * Keep in mind that it will be fed through icache hash function too.
   */
  static inline unsigned long hash(dev_t dev)
  {
  	return MAJOR(dev)+MINOR(dev);
  }
  
  static int bdev_test(struct inode *inode, void *data)
  {
  	return BDEV_I(inode)->bdev.bd_dev == *(dev_t *)data;
  }
  
  static int bdev_set(struct inode *inode, void *data)
  {
  	BDEV_I(inode)->bdev.bd_dev = *(dev_t *)data;
  	return 0;
  }

  static struct block_device *bdget(dev_t dev)

  {
  	struct block_device *bdev;
  	struct inode *inode;

  	inode = iget5_locked(blockdev_superblock, hash(dev),

  			bdev_test, bdev_set, &dev);
  
  	if (!inode)
  		return NULL;
  
  	bdev = &BDEV_I(inode)->bdev;
  
  	if (inode->i_state & I_NEW) {

  		spin_lock_init(&bdev->bd_size_lock);

  		bdev->bd_contains = NULL;

  		bdev->bd_super = NULL;

  		bdev->bd_inode = inode;

  		bdev->bd_part_count = 0;

  		inode->i_mode = S_IFBLK;
  		inode->i_rdev = dev;
  		inode->i_bdev = bdev;
  		inode->i_data.a_ops = &def_blk_aops;
  		mapping_set_gfp_mask(&inode->i_data, GFP_USER);

  		unlock_new_inode(inode);
  	}
  	return bdev;
  }

  /**
   * bdgrab -- Grab a reference to an already referenced block device
   * @bdev:	Block device to grab a reference to.
   */
  struct block_device *bdgrab(struct block_device *bdev)
  {

  	ihold(bdev->bd_inode);

  	return bdev;
  }

  EXPORT_SYMBOL(bdgrab);

  struct block_device *bdget_part(struct hd_struct *part)
  {
  	return bdget(part_devt(part));
  }

  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;
  }
  
  void bdput(struct block_device *bdev)
  {
  	iput(bdev->bd_inode);
  }
  
  EXPORT_SYMBOL(bdput);
   
  static struct block_device *bd_acquire(struct inode *inode)
  {
  	struct block_device *bdev;

  	spin_lock(&bdev_lock);
  	bdev = inode->i_bdev;

  	if (bdev && !inode_unhashed(bdev->bd_inode)) {

  		bdgrab(bdev);

  		spin_unlock(&bdev_lock);
  		return bdev;
  	}
  	spin_unlock(&bdev_lock);

  	/*
  	 * i_bdev references block device inode that was already shut down
  	 * (corresponding device got removed).  Remove the reference and look
  	 * up block device inode again just in case new device got
  	 * reestablished under the same device number.
  	 */
  	if (bdev)
  		bd_forget(inode);

  	bdev = bdget(inode->i_rdev);
  	if (bdev) {
  		spin_lock(&bdev_lock);

  		if (!inode->i_bdev) {
  			/*

  			 * We take an additional reference to bd_inode,

  			 * and it's released in clear_inode() of inode.
  			 * So, we can access it via ->i_mapping always
  			 * without igrab().
  			 */

  			bdgrab(bdev);

  			inode->i_bdev = bdev;
  			inode->i_mapping = bdev->bd_inode->i_mapping;

  		}

  		spin_unlock(&bdev_lock);
  	}
  	return bdev;
  }
  
  /* Call when you free inode */
  
  void bd_forget(struct inode *inode)
  {

  	struct block_device *bdev = NULL;

  	spin_lock(&bdev_lock);

  	if (!sb_is_blkdev_sb(inode->i_sb))
  		bdev = inode->i_bdev;

  	inode->i_bdev = NULL;
  	inode->i_mapping = &inode->i_data;

  	spin_unlock(&bdev_lock);

  
  	if (bdev)

  		bdput(bdev);

  }

  /**
   * 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
   * @whole: the whole device containing @bdev, may equal @bdev
   * @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, struct block_device *whole,
  		void *holder)

  {
  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 struct gendisk *bdev_get_gendisk(struct block_device *bdev, int *partno)
  {
  	struct gendisk *disk = get_gendisk(bdev->bd_dev, partno);
  
  	if (!disk)
  		return NULL;
  	/*
  	 * Now that we hold gendisk reference we make sure bdev we looked up is
  	 * not stale. If it is, it means device got removed and created before
  	 * we looked up gendisk and we fail open in such case. Associating
  	 * unhashed bdev with newly created gendisk could lead to two bdevs
  	 * (and thus two independent caches) being associated with one device
  	 * which is bad.
  	 */
  	if (inode_unhashed(bdev->bd_inode)) {
  		put_disk_and_module(disk);
  		return NULL;
  	}
  	return disk;
  }

  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

   * @whole: whole block device

   * @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,
  		struct block_device *whole, void *holder)

  {
  	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

   * @whole: whole block device

   * @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, struct block_device *whole,
  		       void *holder)
  {
  	spin_lock(&bdev_lock);
  	bd_clear_claiming(whole, holder);
  	spin_unlock(&bdev_lock);
  }
  EXPORT_SYMBOL(bd_abort_claiming);

  #ifdef CONFIG_SYSFS

  struct bd_holder_disk {
  	struct list_head	list;
  	struct gendisk		*disk;
  	int			refcnt;
  };
  
  static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
  						  struct gendisk *disk)
  {
  	struct bd_holder_disk *holder;
  
  	list_for_each_entry(holder, &bdev->bd_holder_disks, list)
  		if (holder->disk == disk)
  			return holder;
  	return NULL;
  }

  static int add_symlink(struct kobject *from, struct kobject *to)

  {

  	return sysfs_create_link(from, to, kobject_name(to));

  }
  
  static void del_symlink(struct kobject *from, struct kobject *to)
  {

  	sysfs_remove_link(from, kobject_name(to));
  }

  /**

   * bd_link_disk_holder - create symlinks between holding disk and slave bdev
   * @bdev: the claimed slave bdev
   * @disk: the holding disk

   *

   * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
   *

   * This functions creates the following sysfs symlinks.

   *

   * - from "slaves" directory of the holder @disk to the claimed @bdev
   * - from "holders" directory of the @bdev to the holder @disk

   *

   * For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is
   * passed to bd_link_disk_holder(), then:

   *

   *   /sys/block/dm-0/slaves/sda --> /sys/block/sda
   *   /sys/block/sda/holders/dm-0 --> /sys/block/dm-0

   *

   * The caller must have claimed @bdev before calling this function and
   * ensure that both @bdev and @disk are valid during the creation and
   * lifetime of these symlinks.

   *

   * CONTEXT:
   * Might sleep.

   *

   * RETURNS:
   * 0 on success, -errno on failure.

   */

  int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)

  {

  	struct bd_holder_disk *holder;

  	int ret = 0;

  	mutex_lock(&bdev->bd_mutex);

  	WARN_ON_ONCE(!bdev->bd_holder);

  	/* FIXME: remove the following once add_disk() handles errors */
  	if (WARN_ON(!disk->slave_dir || !bdev->bd_part->holder_dir))
  		goto out_unlock;

  	holder = bd_find_holder_disk(bdev, disk);
  	if (holder) {
  		holder->refcnt++;

  		goto out_unlock;

  	}

  	holder = kzalloc(sizeof(*holder), GFP_KERNEL);
  	if (!holder) {
  		ret = -ENOMEM;

  		goto out_unlock;
  	}

  	INIT_LIST_HEAD(&holder->list);
  	holder->disk = disk;
  	holder->refcnt = 1;
  
  	ret = add_symlink(disk->slave_dir, &part_to_dev(bdev->bd_part)->kobj);
  	if (ret)
  		goto out_free;
  
  	ret = add_symlink(bdev->bd_part->holder_dir, &disk_to_dev(disk)->kobj);
  	if (ret)
  		goto out_del;

  	/*
  	 * bdev could be deleted beneath us which would implicitly destroy
  	 * the holder directory.  Hold on to it.
  	 */
  	kobject_get(bdev->bd_part->holder_dir);

  
  	list_add(&holder->list, &bdev->bd_holder_disks);
  	goto out_unlock;
  
  out_del:
  	del_symlink(disk->slave_dir, &part_to_dev(bdev->bd_part)->kobj);
  out_free:
  	kfree(holder);

  out_unlock:

  	mutex_unlock(&bdev->bd_mutex);

  	return ret;

  }

  EXPORT_SYMBOL_GPL(bd_link_disk_holder);

  /**
   * bd_unlink_disk_holder - destroy symlinks created by bd_link_disk_holder()
   * @bdev: the calimed slave bdev
   * @disk: the holding disk
   *
   * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
   *
   * CONTEXT:
   * Might sleep.
   */
  void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)

  {

  	struct bd_holder_disk *holder;

  	mutex_lock(&bdev->bd_mutex);

  	holder = bd_find_holder_disk(bdev, disk);
  
  	if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
  		del_symlink(disk->slave_dir, &part_to_dev(bdev->bd_part)->kobj);
  		del_symlink(bdev->bd_part->holder_dir,
  			    &disk_to_dev(disk)->kobj);

  		kobject_put(bdev->bd_part->holder_dir);

  		list_del_init(&holder->list);
  		kfree(holder);
  	}
  
  	mutex_unlock(&bdev->bd_mutex);

  }

  EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);

  #endif

  /**

   * check_disk_size_change - checks for disk size change and adjusts bdev size.

   * @disk: struct gendisk to check
   * @bdev: struct bdev to adjust.

   * @verbose: if %true log a message about a size change if there is any

   *
   * This routine checks to see if the bdev size does not match the disk size

   * and adjusts it if it differs. When shrinking the bdev size, its all caches
   * are freed.

   */

  static void check_disk_size_change(struct gendisk *disk,
  		struct block_device *bdev, bool verbose)

  {
  	loff_t disk_size, bdev_size;

  	spin_lock(&bdev->bd_size_lock);

  	disk_size = (loff_t)get_capacity(disk) << 9;
  	bdev_size = i_size_read(bdev->bd_inode);
  	if (disk_size != bdev_size) {

  		if (verbose) {
  			printk(KERN_INFO
  			       "%s: detected capacity change from %lld to %lld
  ",
  			       disk->disk_name, bdev_size, disk_size);
  		}

  		i_size_write(bdev->bd_inode, disk_size);

  	}

  	spin_unlock(&bdev->bd_size_lock);
  
  	if (bdev_size > disk_size) {
  		if (__invalidate_device(bdev, false))

  			pr_warn("VFS: busy inodes on resized disk %s
  ",
  				disk->disk_name);

  	}
  }

  
  /**

   * revalidate_disk_size - checks for disk size change and adjusts bdev size.
   * @disk: struct gendisk to check
   * @verbose: if %true log a message about a size change if there is any
   *
   * This routine checks to see if the bdev size does not match the disk size
   * and adjusts it if it differs. When shrinking the bdev size, its all caches
   * are freed.
   */
  void revalidate_disk_size(struct gendisk *disk, bool verbose)
  {
  	struct block_device *bdev;
  
  	/*
  	 * Hidden disks don't have associated bdev so there's no point in
  	 * revalidating them.
  	 */
  	if (disk->flags & GENHD_FL_HIDDEN)
  		return;
  
  	bdev = bdget_disk(disk, 0);
  	if (bdev) {
  		check_disk_size_change(disk, bdev, verbose);
  		bdput(bdev);
  	}
  }
  EXPORT_SYMBOL(revalidate_disk_size);

  void bd_set_nr_sectors(struct block_device *bdev, sector_t sectors)

  {

  	spin_lock(&bdev->bd_size_lock);

  	i_size_write(bdev->bd_inode, (loff_t)sectors << SECTOR_SHIFT);

  	spin_unlock(&bdev->bd_size_lock);

  }

  EXPORT_SYMBOL(bd_set_nr_sectors);

  static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part);

  int bdev_disk_changed(struct block_device *bdev, bool invalidate)

  {

  	struct gendisk *disk = bdev->bd_disk;

  	int ret;

  	lockdep_assert_held(&bdev->bd_mutex);

  	clear_bit(GD_NEED_PART_SCAN, &bdev->bd_disk->state);

  rescan:

  	ret = blk_drop_partitions(bdev);

  	if (ret)
  		return ret;

  	/*
  	 * Historically we only set the capacity to zero for devices that
  	 * support partitions (independ of actually having partitions created).
  	 * Doing that is rather inconsistent, but changing it broke legacy
  	 * udisks polling for legacy ide-cdrom devices.  Use the crude check
  	 * below to get the sane behavior for most device while not breaking
  	 * userspace for this particular setup.
  	 */
  	if (invalidate) {
  		if (disk_part_scan_enabled(disk) ||
  		    !(disk->flags & GENHD_FL_REMOVABLE))
  			set_capacity(disk, 0);
  	} else {
  		if (disk->fops->revalidate_disk)
  			disk->fops->revalidate_disk(disk);
  	}

  
  	check_disk_size_change(disk, bdev, !invalidate);

  	if (get_capacity(disk)) {
  		ret = blk_add_partitions(disk, bdev);
  		if (ret == -EAGAIN)
  			goto rescan;

  	} else if (invalidate) {

  		/*
  		 * Tell userspace that the media / partition table may have
  		 * changed.
  		 */
  		kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);

  	}

  	return ret;
  }

  /*
   * Only exported for for loop and dasd for historic reasons.  Don't use in new
   * code!
   */
  EXPORT_SYMBOL_GPL(bdev_disk_changed);

  /*
   * bd_mutex locking:
   *
   *  mutex_lock(part->bd_mutex)
   *    mutex_lock_nested(whole->bd_mutex, 1)
   */

  static int __blkdev_get(struct block_device *bdev, fmode_t mode, void *holder,
  		int for_part)

  {

  	struct block_device *whole = NULL, *claiming = NULL;

  	struct gendisk *disk;

  	int ret;

  	int partno;

  	bool first_open = false, unblock_events = true, need_restart;

   restart:

  	need_restart = false;

  	ret = -ENXIO;

  	disk = bdev_get_gendisk(bdev, &partno);

  	if (!disk)

  		goto out;

  	if (partno) {
  		whole = bdget_disk(disk, 0);
  		if (!whole) {
  			ret = -ENOMEM;
  			goto out_put_disk;
  		}
  	}
  
  	if (!for_part && (mode & FMODE_EXCL)) {
  		WARN_ON_ONCE(!holder);
  		if (whole)
  			claiming = whole;
  		else
  			claiming = bdev;
  		ret = bd_prepare_to_claim(bdev, claiming, holder);
  		if (ret)
  			goto out_put_whole;
  	}

  	disk_block_events(disk);

  	mutex_lock_nested(&bdev->bd_mutex, for_part);

  	if (!bdev->bd_openers) {

  		first_open = true;

  		bdev->bd_disk = disk;
  		bdev->bd_contains = bdev;

  		bdev->bd_partno = partno;

  		if (!partno) {

  			ret = -ENXIO;
  			bdev->bd_part = disk_get_part(disk, partno);
  			if (!bdev->bd_part)
  				goto out_clear;

  			ret = 0;

  			if (disk->fops->open) {

  				ret = disk->fops->open(bdev, mode);

  				/*
  				 * If we lost a race with 'disk' being deleted,
  				 * try again.  See md.c
  				 */
  				if (ret == -ERESTARTSYS)
  					need_restart = true;

  			}

  			if (!ret) {

  				bd_set_nr_sectors(bdev, get_capacity(disk));

  				set_init_blocksize(bdev);
  			}

  			/*
  			 * If the device is invalidated, rescan partition
  			 * if open succeeded or failed with -ENOMEDIUM.
  			 * The latter is necessary to prevent ghost
  			 * partitions on a removed medium.
  			 */

  			if (test_bit(GD_NEED_PART_SCAN, &disk->state) &&

  			    (!ret || ret == -ENOMEDIUM))
  				bdev_disk_changed(bdev, ret == -ENOMEDIUM);

  			if (ret)
  				goto out_clear;

  		} else {

  			BUG_ON(for_part);

  			ret = __blkdev_get(whole, mode, NULL, 1);
  			if (ret)

  				goto out_clear;

  			bdev->bd_contains = bdgrab(whole);

  			bdev->bd_part = disk_get_part(disk, partno);

  			if (!(disk->flags & GENHD_FL_UP) ||

  			    !bdev->bd_part || !bdev->bd_part->nr_sects) {

  				ret = -ENXIO;

  				goto out_clear;

  			}

  			bd_set_nr_sectors(bdev, bdev->bd_part->nr_sects);

  			set_init_blocksize(bdev);

  		}

  
  		if (bdev->bd_bdi == &noop_backing_dev_info)
  			bdev->bd_bdi = bdi_get(disk->queue->backing_dev_info);

  	} else {

  		if (bdev->bd_contains == bdev) {

  			ret = 0;
  			if (bdev->bd_disk->fops->open)

  				ret = bdev->bd_disk->fops->open(bdev, mode);

  			/* the same as first opener case, read comment there */

  			if (test_bit(GD_NEED_PART_SCAN, &disk->state) &&

  			    (!ret || ret == -ENOMEDIUM))
  				bdev_disk_changed(bdev, ret == -ENOMEDIUM);

  			if (ret)
  				goto out_unlock_bdev;

  		}
  	}
  	bdev->bd_openers++;

  	if (for_part)
  		bdev->bd_part_count++;

  	if (claiming)
  		bd_finish_claiming(bdev, claiming, 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 (claiming && (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(&bdev->bd_mutex);

  
  	if (unblock_events)
  		disk_unblock_events(disk);

  	/* only one opener holds refs to the module and disk */
  	if (!first_open)
  		put_disk_and_module(disk);

  	if (whole)
  		bdput(whole);

  	return 0;

   out_clear:

  	disk_put_part(bdev->bd_part);

  	bdev->bd_disk = NULL;

  	bdev->bd_part = NULL;

  	if (bdev != bdev->bd_contains)

  		__blkdev_put(bdev->bd_contains, mode, 1);

  	bdev->bd_contains = NULL;

   out_unlock_bdev:

  	if (claiming)
  		bd_abort_claiming(bdev, claiming, holder);

  	mutex_unlock(&bdev->bd_mutex);

  	disk_unblock_events(disk);

   out_put_whole:
   	if (whole)
  		bdput(whole);
   out_put_disk:

  	put_disk_and_module(disk);

  	if (need_restart)
  		goto restart;

   out:

  	return ret;
  }

  /**
   * blkdev_get - open a block device
   * @bdev: block_device to open
   * @mode: FMODE_* mask
   * @holder: exclusive holder identifier
   *
   * Open @bdev with @mode.  If @mode includes %FMODE_EXCL, @bdev is
   * open with exclusive access.  Specifying %FMODE_EXCL with %NULL
   * @holder is invalid.  Exclusive opens may nest for the same @holder.
   *
   * On success, the reference count of @bdev is unchanged.  On failure,
   * @bdev is put.
   *
   * CONTEXT:
   * Might sleep.
   *
   * RETURNS:
   * 0 on success, -errno on failure.
   */

  static int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)

  {

  	int ret, perm = 0;

  	if (mode & FMODE_READ)
  		perm |= MAY_READ;
  	if (mode & FMODE_WRITE)
  		perm |= MAY_WRITE;
  	ret = devcgroup_inode_permission(bdev->bd_inode, perm);
  	if (ret)
  		goto bdput;
  
  	ret =__blkdev_get(bdev, mode, holder, 0);
  	if (ret)
  		goto bdput;
  	return 0;
  
  bdput:
  	bdput(bdev);
  	return ret;

  }

  /**
   * 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 blockdevice described by the device file at @path.  @mode
   * and @holder are identical to blkdev_get().
   *
   * On success, the returned block_device has reference count of one.
   *
   * CONTEXT:
   * Might sleep.
   *
   * RETURNS:
   * Pointer to 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;
  	int err;
  
  	bdev = lookup_bdev(path);
  	if (IS_ERR(bdev))
  		return bdev;
  
  	err = blkdev_get(bdev, mode, holder);
  	if (err)
  		return ERR_PTR(err);

  	if ((mode & FMODE_WRITE) && bdev_read_only(bdev)) {
  		blkdev_put(bdev, mode);
  		return ERR_PTR(-EACCES);
  	}

  	return bdev;
  }
  EXPORT_SYMBOL(blkdev_get_by_path);
  
  /**
   * 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 blockdevice described by device number @dev.  @mode and
   * @holder are identical to blkdev_get().
   *
   * Use it 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.  _Never_ to be used for internal purposes.  If you
   * ever need it - reconsider your API.
   *
   * On success, the returned block_device has reference count of one.
   *
   * CONTEXT:
   * Might sleep.
   *
   * RETURNS:
   * Pointer to block_device on success, ERR_PTR(-errno) on failure.
   */
  struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
  {
  	struct block_device *bdev;
  	int err;
  
  	bdev = bdget(dev);
  	if (!bdev)
  		return ERR_PTR(-ENOMEM);
  
  	err = blkdev_get(bdev, mode, holder);
  	if (err)
  		return ERR_PTR(err);
  
  	return bdev;
  }
  EXPORT_SYMBOL(blkdev_get_by_dev);

  static int blkdev_open(struct inode * inode, struct file * filp)
  {
  	struct block_device *bdev;