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block_dev.c

/*
 *  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/smp_lock.h>
#include <linux/highmem.h>
#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/blkpg.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <linux/mpage.h>
#include <linux/mount.h>
#include <linux/uio.h>
#include <linux/namei.h>
#include <linux/log2.h>
#include <asm/uaccess.h>
#include "internal.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);
}

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

EXPORT_SYMBOL(I_BDEV);

static sector_t max_block(struct block_device *bdev)
{
      sector_t retval = ~((sector_t)0);
      loff_t sz = i_size_read(bdev->bd_inode);

      if (sz) {
            unsigned int size = block_size(bdev);
            unsigned int sizebits = blksize_bits(size);
            retval = (sz >> sizebits);
      }
      return retval;
}

/* Kill _all_ buffers and pagecache , dirty or not.. */
static void kill_bdev(struct block_device *bdev)
{
      if (bdev->bd_inode->i_mapping->nrpages == 0)
            return;
      invalidate_bh_lrus();
      truncate_inode_pages(bdev->bd_inode->i_mapping, 0);
}     

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_hardsect_size(bdev))
            return -EINVAL;

      /* Don't change the size if it is same as current */
      if (bdev->bd_block_size != size) {
            sync_blockdev(bdev);
            bdev->bd_block_size = size;
            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_hardsect_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)
{
      if (iblock >= max_block(I_BDEV(inode))) {
            if (create)
                  return -EIO;

            /*
             * for reads, we're just trying to fill a partial page.
             * return a hole, they will have to call get_block again
             * before they can fill it, and they will get -EIO at that
             * time
             */
            return 0;
      }
      bh->b_bdev = I_BDEV(inode);
      bh->b_blocknr = iblock;
      set_buffer_mapped(bh);
      return 0;
}

static int
blkdev_get_blocks(struct inode *inode, sector_t iblock,
            struct buffer_head *bh, int create)
{
      sector_t end_block = max_block(I_BDEV(inode));
      unsigned long max_blocks = bh->b_size >> inode->i_blkbits;

      if ((iblock + max_blocks) > end_block) {
            max_blocks = end_block - iblock;
            if ((long)max_blocks <= 0) {
                  if (create)
                        return -EIO;      /* write fully beyond EOF */
                  /*
                   * It is a read which is fully beyond EOF.  We return
                   * a !buffer_mapped buffer
                   */
                  max_blocks = 0;
            }
      }

      bh->b_bdev = I_BDEV(inode);
      bh->b_blocknr = iblock;
      bh->b_size = max_blocks << inode->i_blkbits;
      if (max_blocks)
            set_buffer_mapped(bh);
      return 0;
}

static ssize_t
blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
                  loff_t offset, unsigned long nr_segs)
{
      struct file *file = iocb->ki_filp;
      struct inode *inode = file->f_mapping->host;

      return blockdev_direct_IO_no_locking(rw, iocb, inode, I_BDEV(inode),
                        iov, offset, nr_segs, blkdev_get_blocks, NULL);
}

#if 0
static void blk_end_aio(struct bio *bio, int error)
{
      struct kiocb *iocb = bio->bi_private;
      atomic_t *bio_count = &iocb->ki_bio_count;

      if (bio_data_dir(bio) == READ)
            bio_check_pages_dirty(bio);
      else {
            bio_release_pages(bio);
            bio_put(bio);
      }

      /* iocb->ki_nbytes stores error code from LLDD */
      if (error)
            iocb->ki_nbytes = -EIO;

      if (atomic_dec_and_test(bio_count)) {
            if ((long)iocb->ki_nbytes < 0)
                  aio_complete(iocb, iocb->ki_nbytes, 0);
            else
                  aio_complete(iocb, iocb->ki_left, 0);
      }

      return 0;
}

#define VEC_SIZE  16
struct pvec {
      unsigned short nr;
      unsigned short idx;
      struct page *page[VEC_SIZE];
};

#define PAGES_SPANNED(addr, len)    \
      (DIV_ROUND_UP((addr) + (len), PAGE_SIZE) - (addr) / PAGE_SIZE);

/*
 * get page pointer for user addr, we internally cache struct page array for
 * (addr, count) range in pvec to avoid frequent call to get_user_pages.  If
 * internal page list is exhausted, a batch count of up to VEC_SIZE is used
 * to get next set of page struct.
 */
static struct page *blk_get_page(unsigned long addr, size_t count, int rw,
                         struct pvec *pvec)
{
      int ret, nr_pages;
      if (pvec->idx == pvec->nr) {
            nr_pages = PAGES_SPANNED(addr, count);
            nr_pages = min(nr_pages, VEC_SIZE);
            down_read(&current->mm->mmap_sem);
            ret = get_user_pages(current, current->mm, addr, nr_pages,
                             rw == READ, 0, pvec->page, NULL);
            up_read(&current->mm->mmap_sem);
            if (ret < 0)
                  return ERR_PTR(ret);
            pvec->nr = ret;
            pvec->idx = 0;
      }
      return pvec->page[pvec->idx++];
}

/* return a page back to pvec array */
static void blk_unget_page(struct page *page, struct pvec *pvec)
{
      pvec->page[--pvec->idx] = page;
}

static ssize_t
blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
             loff_t pos, unsigned long nr_segs)
{
      struct inode *inode = iocb->ki_filp->f_mapping->host;
      unsigned blkbits = blksize_bits(bdev_hardsect_size(I_BDEV(inode)));
      unsigned blocksize_mask = (1 << blkbits) - 1;
      unsigned long seg = 0;  /* iov segment iterator */
      unsigned long nvec;     /* number of bio vec needed */
      unsigned long cur_off;  /* offset into current page */
      unsigned long cur_len;  /* I/O len of current page, up to PAGE_SIZE */

      unsigned long addr;     /* user iovec address */
      size_t count;           /* user iovec len */
      size_t nbytes = iocb->ki_nbytes = iocb->ki_left; /* total xfer size */
      loff_t size;            /* size of block device */
      struct bio *bio;
      atomic_t *bio_count = &iocb->ki_bio_count;
      struct page *page;
      struct pvec pvec;

      pvec.nr = 0;
      pvec.idx = 0;

      if (pos & blocksize_mask)
            return -EINVAL;

      size = i_size_read(inode);
      if (pos + nbytes > size) {
            nbytes = size - pos;
            iocb->ki_left = nbytes;
      }

      /*
       * check first non-zero iov alignment, the remaining
       * iov alignment is checked inside bio loop below.
       */
      do {
            addr = (unsigned long) iov[seg].iov_base;
            count = min(iov[seg].iov_len, nbytes);
            if (addr & blocksize_mask || count & blocksize_mask)
                  return -EINVAL;
      } while (!count && ++seg < nr_segs);
      atomic_set(bio_count, 1);

      while (nbytes) {
            /* roughly estimate number of bio vec needed */
            nvec = (nbytes + PAGE_SIZE - 1) / PAGE_SIZE;
            nvec = max(nvec, nr_segs - seg);
            nvec = min(nvec, (unsigned long) BIO_MAX_PAGES);

            /* bio_alloc should not fail with GFP_KERNEL flag */
            bio = bio_alloc(GFP_KERNEL, nvec);
            bio->bi_bdev = I_BDEV(inode);
            bio->bi_end_io = blk_end_aio;
            bio->bi_private = iocb;
            bio->bi_sector = pos >> blkbits;
same_bio:
            cur_off = addr & ~PAGE_MASK;
            cur_len = PAGE_SIZE - cur_off;
            if (count < cur_len)
                  cur_len = count;

            page = blk_get_page(addr, count, rw, &pvec);
            if (unlikely(IS_ERR(page)))
                  goto backout;

            if (bio_add_page(bio, page, cur_len, cur_off)) {
                  pos += cur_len;
                  addr += cur_len;
                  count -= cur_len;
                  nbytes -= cur_len;

                  if (count)
                        goto same_bio;
                  while (++seg < nr_segs) {
                        addr = (unsigned long) iov[seg].iov_base;
                        count = iov[seg].iov_len;
                        if (!count)
                              continue;
                        if (unlikely(addr & blocksize_mask ||
                                   count & blocksize_mask)) {
                              page = ERR_PTR(-EINVAL);
                              goto backout;
                        }
                        count = min(count, nbytes);
                        goto same_bio;
                  }
            } else {
                  blk_unget_page(page, &pvec);
            }

            /* bio is ready, submit it */
            if (rw == READ)
                  bio_set_pages_dirty(bio);
            atomic_inc(bio_count);
            submit_bio(rw, bio);
      }

completion:
      iocb->ki_left -= nbytes;
      nbytes = iocb->ki_left;
      iocb->ki_pos += nbytes;

      blk_run_address_space(inode->i_mapping);
      if (atomic_dec_and_test(bio_count))
            aio_complete(iocb, nbytes, 0);

      return -EIOCBQUEUED;

backout:
      /*
       * back out nbytes count constructed so far for this bio,
       * we will throw away current bio.
       */
      nbytes += bio->bi_size;
      bio_release_pages(bio);
      bio_put(bio);

      /*
       * if no bio was submmitted, return the error code.
       * otherwise, proceed with pending I/O completion.
       */
      if (atomic_read(bio_count) == 1)
            return PTR_ERR(page);
      goto completion;
}
#endif

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 int blkdev_write_begin(struct file *file, struct address_space *mapping,
                  loff_t pos, unsigned len, unsigned flags,
                  struct page **pagep, void **fsdata)
{
      *pagep = NULL;
      return block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
                        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);
      page_cache_release(page);

      return ret;
}

/*
 * private llseek:
 * for a block special file file->f_path.dentry->d_inode->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 origin)
{
      struct inode *bd_inode = file->f_mapping->host;
      loff_t size;
      loff_t retval;

      mutex_lock(&bd_inode->i_mutex);
      size = i_size_read(bd_inode);

      switch (origin) {
            case 2:
                  offset += size;
                  break;
            case 1:
                  offset += file->f_pos;
      }
      retval = -EINVAL;
      if (offset >= 0 && offset <= size) {
            if (offset != file->f_pos) {
                  file->f_pos = offset;
            }
            retval = offset;
      }
      mutex_unlock(&bd_inode->i_mutex);
      return retval;
}
      
/*
 *    Filp is never NULL; the only case when ->fsync() is called with
 *    NULL first argument is nfsd_sync_dir() and that's not a directory.
 */
 
static int block_fsync(struct file *filp, struct dentry *dentry, int datasync)
{
      return sync_blockdev(I_BDEV(filp->f_mapping->host));
}

/*
 * 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_destroy_inode(struct inode *inode)
{
      struct bdev_inode *bdi = BDEV_I(inode);

      bdi->bdev.bd_inode_backing_dev_info = NULL;
      kmem_cache_free(bdev_cachep, bdi);
}

static void init_once(struct kmem_cache * cachep, 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);
      sema_init(&bdev->bd_mount_sem, 1);
      INIT_LIST_HEAD(&bdev->bd_inodes);
      INIT_LIST_HEAD(&bdev->bd_list);
#ifdef CONFIG_SYSFS
      INIT_LIST_HEAD(&bdev->bd_holder_list);
#endif
      inode_init_once(&ei->vfs_inode);
}

static inline void __bd_forget(struct inode *inode)
{
      list_del_init(&inode->i_devices);
      inode->i_bdev = NULL;
      inode->i_mapping = &inode->i_data;
}

static void bdev_clear_inode(struct inode *inode)
{
      struct block_device *bdev = &BDEV_I(inode)->bdev;
      struct list_head *p;
      spin_lock(&bdev_lock);
      while ( (p = bdev->bd_inodes.next) != &bdev->bd_inodes ) {
            __bd_forget(list_entry(p, struct inode, i_devices));
      }
      list_del_init(&bdev->bd_list);
      spin_unlock(&bdev_lock);
}

static const struct super_operations bdev_sops = {
      .statfs = simple_statfs,
      .alloc_inode = bdev_alloc_inode,
      .destroy_inode = bdev_destroy_inode,
      .drop_inode = generic_delete_inode,
      .clear_inode = bdev_clear_inode,
};

static int bd_get_sb(struct file_system_type *fs_type,
      int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
      return get_sb_pseudo(fs_type, "bdev:", &bdev_sops, 0x62646576, mnt);
}

static struct file_system_type bd_type = {
      .name       = "bdev",
      .get_sb           = bd_get_sb,
      .kill_sb    = kill_anon_super,
};

static struct vfsmount *bd_mnt __read_mostly;
struct super_block *blockdev_superblock;

void __init bdev_cache_init(void)
{
      int err;
      bdev_cachep = kmem_cache_create("bdev_cache", sizeof(struct bdev_inode),
                  0, (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
                        SLAB_MEM_SPREAD|SLAB_PANIC),
                  init_once);
      err = register_filesystem(&bd_type);
      if (err)
            panic("Cannot register bdev pseudo-fs");
      bd_mnt = kern_mount(&bd_type);
      err = PTR_ERR(bd_mnt);
      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 LIST_HEAD(all_bdevs);

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

      inode = iget5_locked(bd_mnt->mnt_sb, hash(dev),
                  bdev_test, bdev_set, &dev);

      if (!inode)
            return NULL;

      bdev = &BDEV_I(inode)->bdev;

      if (inode->i_state & I_NEW) {
            bdev->bd_contains = NULL;
            bdev->bd_inode = inode;
            bdev->bd_block_size = (1 << inode->i_blkbits);
            bdev->bd_part_count = 0;
            bdev->bd_invalidated = 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);
            inode->i_data.backing_dev_info = &default_backing_dev_info;
            spin_lock(&bdev_lock);
            list_add(&bdev->bd_list, &all_bdevs);
            spin_unlock(&bdev_lock);
            unlock_new_inode(inode);
      }
      return bdev;
}

EXPORT_SYMBOL(bdget);

long nr_blockdev_pages(void)
{
      struct block_device *bdev;
      long ret = 0;
      spin_lock(&bdev_lock);
      list_for_each_entry(bdev, &all_bdevs, bd_list) {
            ret += bdev->bd_inode->i_mapping->nrpages;
      }
      spin_unlock(&bdev_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) {
            atomic_inc(&bdev->bd_inode->i_count);
            spin_unlock(&bdev_lock);
            return bdev;
      }
      spin_unlock(&bdev_lock);

      bdev = bdget(inode->i_rdev);
      if (bdev) {
            spin_lock(&bdev_lock);
            if (!inode->i_bdev) {
                  /*
                   * We take an additional bd_inode->i_count for inode,
                   * and it's released in clear_inode() of inode.
                   * So, we can access it via ->i_mapping always
                   * without igrab().
                   */
                  atomic_inc(&bdev->bd_inode->i_count);
                  inode->i_bdev = bdev;
                  inode->i_mapping = bdev->bd_inode->i_mapping;
                  list_add(&inode->i_devices, &bdev->bd_inodes);
            }
            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 (inode->i_bdev) {
            if (inode->i_sb != blockdev_superblock)
                  bdev = inode->i_bdev;
            __bd_forget(inode);
      }
      spin_unlock(&bdev_lock);

      if (bdev)
            iput(bdev->bd_inode);
}

int bd_claim(struct block_device *bdev, void *holder)
{
      int res;
      spin_lock(&bdev_lock);

      /* first decide result */
      if (bdev->bd_holder == holder)
            res = 0;     /* already a holder */
      else if (bdev->bd_holder != NULL)
            res = -EBUSY;      /* held by someone else */
      else if (bdev->bd_contains == bdev)
            res = 0;     /* is a whole device which isn't held */

      else if (bdev->bd_contains->bd_holder == bd_claim)
            res = 0;     /* is a partition of a device that is being partitioned */
      else if (bdev->bd_contains->bd_holder != NULL)
            res = -EBUSY;      /* is a partition of a held device */
      else
            res = 0;     /* is a partition of an un-held device */

      /* now impose change */
      if (res==0) {
            /* note that for a whole device bd_holders
             * will be incremented twice, and bd_holder will
             * be set to bd_claim before being set to holder
             */
            bdev->bd_contains->bd_holders ++;
            bdev->bd_contains->bd_holder = bd_claim;
            bdev->bd_holders++;
            bdev->bd_holder = holder;
      }
      spin_unlock(&bdev_lock);
      return res;
}

EXPORT_SYMBOL(bd_claim);

void bd_release(struct block_device *bdev)
{
      spin_lock(&bdev_lock);
      if (!--bdev->bd_contains->bd_holders)
            bdev->bd_contains->bd_holder = NULL;
      if (!--bdev->bd_holders)
            bdev->bd_holder = NULL;
      spin_unlock(&bdev_lock);
}

EXPORT_SYMBOL(bd_release);

#ifdef CONFIG_SYSFS
/*
 * Functions for bd_claim_by_kobject / bd_release_from_kobject
 *
 *     If a kobject is passed to bd_claim_by_kobject()
 *     and the kobject has a parent directory,
 *     following symlinks are created:
 *        o from the kobject to the claimed bdev
 *        o from "holders" directory of the bdev to the parent of the kobject
 *     bd_release_from_kobject() removes these symlinks.
 *
 *     Example:
 *        If /dev/dm-0 maps to /dev/sda, kobject corresponding to
 *        /sys/block/dm-0/slaves is passed to bd_claim_by_kobject(), then:
 *           /sys/block/dm-0/slaves/sda --> /sys/block/sda
 *           /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
 */

static struct kobject *bdev_get_kobj(struct block_device *bdev)
{
      if (bdev->bd_contains != bdev)
            return kobject_get(&bdev->bd_part->kobj);
      else
            return kobject_get(&bdev->bd_disk->kobj);
}

static struct kobject *bdev_get_holder(struct block_device *bdev)
{
      if (bdev->bd_contains != bdev)
            return kobject_get(bdev->bd_part->holder_dir);
      else
            return kobject_get(bdev->bd_disk->holder_dir);
}

static int add_symlink(struct kobject *from, struct kobject *to)
{
      if (!from || !to)
            return 0;
      return sysfs_create_link(from, to, kobject_name(to));
}

static void del_symlink(struct kobject *from, struct kobject *to)
{
      if (!from || !to)
            return;
      sysfs_remove_link(from, kobject_name(to));
}

/*
 * 'struct bd_holder' contains pointers to kobjects symlinked by
 * bd_claim_by_kobject.
 * It's connected to bd_holder_list which is protected by bdev->bd_sem.
 */
struct bd_holder {
      struct list_head list;  /* chain of holders of the bdev */
      int count;        /* references from the holder */
      struct kobject *sdir;   /* holder object, e.g. "/block/dm-0/slaves" */
      struct kobject *hdev;   /* e.g. "/block/dm-0" */
      struct kobject *hdir;   /* e.g. "/block/sda/holders" */
      struct kobject *sdev;   /* e.g. "/block/sda" */
};

/*
 * Get references of related kobjects at once.
 * Returns 1 on success. 0 on failure.
 *
 * Should call bd_holder_release_dirs() after successful use.
 */
static int bd_holder_grab_dirs(struct block_device *bdev,
                  struct bd_holder *bo)
{
      if (!bdev || !bo)
            return 0;

      bo->sdir = kobject_get(bo->sdir);
      if (!bo->sdir)
            return 0;

      bo->hdev = kobject_get(bo->sdir->parent);
      if (!bo->hdev)
            goto fail_put_sdir;

      bo->sdev = bdev_get_kobj(bdev);
      if (!bo->sdev)
            goto fail_put_hdev;

      bo->hdir = bdev_get_holder(bdev);
      if (!bo->hdir)
            goto fail_put_sdev;

      return 1;

fail_put_sdev:
      kobject_put(bo->sdev);
fail_put_hdev:
      kobject_put(bo->hdev);
fail_put_sdir:
      kobject_put(bo->sdir);

      return 0;
}

/* Put references of related kobjects at once. */
static void bd_holder_release_dirs(struct bd_holder *bo)
{
      kobject_put(bo->hdir);
      kobject_put(bo->sdev);
      kobject_put(bo->hdev);
      kobject_put(bo->sdir);
}

static struct bd_holder *alloc_bd_holder(struct kobject *kobj)
{
      struct bd_holder *bo;

      bo = kzalloc(sizeof(*bo), GFP_KERNEL);
      if (!bo)
            return NULL;

      bo->count = 1;
      bo->sdir = kobj;

      return bo;
}

static void free_bd_holder(struct bd_holder *bo)
{
      kfree(bo);
}

/**
 * find_bd_holder - find matching struct bd_holder from the block device
 *
 * @bdev:   struct block device to be searched
 * @bo:           target struct bd_holder
 *
 * Returns matching entry with @bo in @bdev->bd_holder_list.
 * If found, increment the reference count and return the pointer.
 * If not found, returns NULL.
 */
static struct bd_holder *find_bd_holder(struct block_device *bdev,
                              struct bd_holder *bo)
{
      struct bd_holder *tmp;

      list_for_each_entry(tmp, &bdev->bd_holder_list, list)
            if (tmp->sdir == bo->sdir) {
                  tmp->count++;
                  return tmp;
            }

      return NULL;
}

/**
 * add_bd_holder - create sysfs symlinks for bd_claim() relationship
 *
 * @bdev:   block device to be bd_claimed
 * @bo:           preallocated and initialized by alloc_bd_holder()
 *
 * Add @bo to @bdev->bd_holder_list, create symlinks.
 *
 * Returns 0 if symlinks are created.
 * Returns -ve if something fails.
 */
static int add_bd_holder(struct block_device *bdev, struct bd_holder *bo)
{
      int err;

      if (!bo)
            return -EINVAL;

      if (!bd_holder_grab_dirs(bdev, bo))
            return -EBUSY;

      err = add_symlink(bo->sdir, bo->sdev);
      if (err)
            return err;

      err = add_symlink(bo->hdir, bo->hdev);
      if (err) {
            del_symlink(bo->sdir, bo->sdev);
            return err;
      }

      list_add_tail(&bo->list, &bdev->bd_holder_list);
      return 0;
}

/**
 * del_bd_holder - delete sysfs symlinks for bd_claim() relationship
 *
 * @bdev:   block device to be bd_claimed
 * @kobj:   holder's kobject
 *
 * If there is matching entry with @kobj in @bdev->bd_holder_list
 * and no other bd_claim() from the same kobject,
 * remove the struct bd_holder from the list, delete symlinks for it.
 *
 * Returns a pointer to the struct bd_holder when it's removed from the list
 * and ready to be freed.
 * Returns NULL if matching claim isn't found or there is other bd_claim()
 * by the same kobject.
 */
static struct bd_holder *del_bd_holder(struct block_device *bdev,
                              struct kobject *kobj)
{
      struct bd_holder *bo;

      list_for_each_entry(bo, &bdev->bd_holder_list, list) {
            if (bo->sdir == kobj) {
                  bo->count--;
                  BUG_ON(bo->count < 0);
                  if (!bo->count) {
                        list_del(&bo->list);
                        del_symlink(bo->sdir, bo->sdev);
                        del_symlink(bo->hdir, bo->hdev);
                        bd_holder_release_dirs(bo);
                        return bo;
                  }
                  break;
            }
      }

      return NULL;
}

/**
 * bd_claim_by_kobject - bd_claim() with additional kobject signature
 *
 * @bdev:   block device to be claimed
 * @holder: holder's signature
 * @kobj:   holder's kobject
 *
 * Do bd_claim() and if it succeeds, create sysfs symlinks between
 * the bdev and the holder's kobject.
 * Use bd_release_from_kobject() when relesing the claimed bdev.
 *
 * Returns 0 on success. (same as bd_claim())
 * Returns errno on failure.
 */
static int bd_claim_by_kobject(struct block_device *bdev, void *holder,
                        struct kobject *kobj)
{
      int err;
      struct bd_holder *bo, *found;

      if (!kobj)
            return -EINVAL;

      bo = alloc_bd_holder(kobj);
      if (!bo)
            return -ENOMEM;

      mutex_lock(&bdev->bd_mutex);

      err = bd_claim(bdev, holder);
      if (err)
            goto fail;

      found = find_bd_holder(bdev, bo);
      if (found)
            goto fail;

      err = add_bd_holder(bdev, bo);
      if (err)
            bd_release(bdev);
      else
            bo = NULL;
fail:
      mutex_unlock(&bdev->bd_mutex);
      free_bd_holder(bo);
      return err;
}

/**
 * bd_release_from_kobject - bd_release() with additional kobject signature
 *
 * @bdev:   block device to be released
 * @kobj:   holder's kobject
 *
 * Do bd_release() and remove sysfs symlinks created by bd_claim_by_kobject().
 */
static void bd_release_from_kobject(struct block_device *bdev,
                              struct kobject *kobj)
{
      if (!kobj)
            return;

      mutex_lock(&bdev->bd_mutex);
      bd_release(bdev);
      free_bd_holder(del_bd_holder(bdev, kobj));
      mutex_unlock(&bdev->bd_mutex);
}

/**
 * bd_claim_by_disk - wrapper function for bd_claim_by_kobject()
 *
 * @bdev:   block device to be claimed
 * @holder: holder's signature
 * @disk:   holder's gendisk
 *
 * Call bd_claim_by_kobject() with getting @disk->slave_dir.
 */
int bd_claim_by_disk(struct block_device *bdev, void *holder,
                  struct gendisk *disk)
{
      return bd_claim_by_kobject(bdev, holder, kobject_get(disk->slave_dir));
}
EXPORT_SYMBOL_GPL(bd_claim_by_disk);

/**
 * bd_release_from_disk - wrapper function for bd_release_from_kobject()
 *
 * @bdev:   block device to be claimed
 * @disk:   holder's gendisk
 *
 * Call bd_release_from_kobject() and put @disk->slave_dir.
 */
void bd_release_from_disk(struct block_device *bdev, struct gendisk *disk)
{
      bd_release_from_kobject(bdev, disk->slave_dir);
      kobject_put(disk->slave_dir);
}
EXPORT_SYMBOL_GPL(bd_release_from_disk);
#endif

/*
 * Tries to open block device by device number.  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.
 */
struct block_device *open_by_devnum(dev_t dev, unsigned mode)
{
      struct block_device *bdev = bdget(dev);
      int err = -ENOMEM;
      int flags = mode & FMODE_WRITE ? O_RDWR : O_RDONLY;
      if (bdev)
            err = blkdev_get(bdev, mode, flags);
      return err ? ERR_PTR(err) : bdev;
}

EXPORT_SYMBOL(open_by_devnum);

/*
 * This routine checks whether a removable media has been changed,
 * and invalidates all buffer-cache-entries in that case. This
 * is a relatively slow routine, so we have to try to minimize using
 * it. Thus it is called only upon a 'mount' or 'open'. This
 * is the best way of combining speed and utility, I think.
 * People changing diskettes in the middle of an operation deserve
 * to lose :-)
 */
int check_disk_change(struct block_device *bdev)
{
      struct gendisk *disk = bdev->bd_disk;
      struct block_device_operations * bdops = disk->fops;

      if (!bdops->media_changed)
            return 0;
      if (!bdops->media_changed(bdev->bd_disk))
            return 0;

      if (__invalidate_device(bdev))
            printk("VFS: busy inodes on changed media.\n");

      if (bdops->revalidate_disk)
            bdops->revalidate_disk(bdev->bd_disk);
      if (bdev->bd_disk->minors > 1)
            bdev->bd_invalidated = 1;
      return 1;
}

EXPORT_SYMBOL(check_disk_change);

void bd_set_size(struct block_device *bdev, loff_t size)
{
      unsigned bsize = bdev_hardsect_size(bdev);

      bdev->bd_inode->i_size = size;
      while (bsize < PAGE_CACHE_SIZE) {
            if (size & bsize)
                  break;
            bsize <<= 1;
      }
      bdev->bd_block_size = bsize;
      bdev->bd_inode->i_blkbits = blksize_bits(bsize);
}
EXPORT_SYMBOL(bd_set_size);

static int __blkdev_get(struct block_device *bdev, mode_t mode, unsigned flags,
                  int for_part);
static int __blkdev_put(struct block_device *bdev, int for_part);

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

static int do_open(struct block_device *bdev, struct file *file, int for_part)
{
      struct module *owner = NULL;
      struct gendisk *disk;
      int ret = -ENXIO;
      int part;

      file->f_mapping = bdev->bd_inode->i_mapping;
      lock_kernel();
      disk = get_gendisk(bdev->bd_dev, &part);
      if (!disk) {
            unlock_kernel();
            bdput(bdev);
            return ret;
      }
      owner = disk->fops->owner;

      mutex_lock_nested(&bdev->bd_mutex, for_part);
      if (!bdev->bd_openers) {
            bdev->bd_disk = disk;
            bdev->bd_contains = bdev;
            if (!part) {
                  struct backing_dev_info *bdi;
                  if (disk->fops->open) {
                        ret = disk->fops->open(bdev->bd_inode, file);
                        if (ret)
                              goto out_first;
                  }
                  if (!bdev->bd_openers) {
                        bd_set_size(bdev,(loff_t)get_capacity(disk)<<9);
                        bdi = blk_get_backing_dev_info(bdev);
                        if (bdi == NULL)
                              bdi = &default_backing_dev_info;
                        bdev->bd_inode->i_data.backing_dev_info = bdi;
                  }
                  if (bdev->bd_invalidated)
                        rescan_partitions(disk, bdev);
            } else {
                  struct hd_struct *p;
                  struct block_device *whole;
                  whole = bdget_disk(disk, 0);
                  ret = -ENOMEM;
                  if (!whole)
                        goto out_first;
                  BUG_ON(for_part);
                  ret = __blkdev_get(whole, file->f_mode, file->f_flags, 1);
                  if (ret)
                        goto out_first;
                  bdev->bd_contains = whole;
                  p = disk->part[part - 1];
                  bdev->bd_inode->i_data.backing_dev_info =
                     whole->bd_inode->i_data.backing_dev_info;
                  if (!(disk->flags & GENHD_FL_UP) || !p || !p->nr_sects) {
                        ret = -ENXIO;
                        goto out_first;
                  }
                  kobject_get(&p->kobj);
                  bdev->bd_part = p;
                  bd_set_size(bdev, (loff_t) p->nr_sects << 9);
            }
      } else {
            put_disk(disk);
            module_put(owner);
            if (bdev->bd_contains == bdev) {
                  if (bdev->bd_disk->fops->open) {
                        ret = bdev->bd_disk->fops->open(bdev->bd_inode, file);
                        if (ret)
                              goto out;
                  }
                  if (bdev->bd_invalidated)
                        rescan_partitions(bdev->bd_disk, bdev);
            }
      }
      bdev->bd_openers++;
      if (for_part)
            bdev->bd_part_count++;
      mutex_unlock(&bdev->bd_mutex);
      unlock_kernel();
      return 0;

out_first:
      bdev->bd_disk = NULL;
      bdev->bd_inode->i_data.backing_dev_info = &default_backing_dev_info;
      if (bdev != bdev->bd_contains)
            __blkdev_put(bdev->bd_contains, 1);
      bdev->bd_contains = NULL;
      put_disk(disk);
      module_put(owner);
out:
      mutex_unlock(&bdev->bd_mutex);
      unlock_kernel();
      if (ret)
            bdput(bdev);
      return ret;
}

static int __blkdev_get(struct block_device *bdev, mode_t mode, unsigned flags,
                  int for_part)
{
      /*
       * This crockload is due to bad choice of ->open() type.
       * It will go away.
       * For now, block device ->open() routine must _not_
       * examine anything in 'inode' argument except ->i_rdev.
       */
      struct file fake_file = {};
      struct dentry fake_dentry = {};
      fake_file.f_mode = mode;
      fake_file.f_flags = flags;
      fake_file.f_path.dentry = &fake_dentry;
      fake_dentry.d_inode = bdev->bd_inode;

      return do_open(bdev, &fake_file, for_part);
}

int blkdev_get(struct block_device *bdev, mode_t mode, unsigned flags)
{
      return __blkdev_get(bdev, mode, flags, 0);
}
EXPORT_SYMBOL(blkdev_get);

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

      /*
       * Preserve backwards compatibility and allow large file access
       * even if userspace doesn't ask for it explicitly. Some mkfs
       * binary needs it. We might want to drop this workaround
       * during an unstable branch.
       */
      filp->f_flags |= O_LARGEFILE;

      bdev = bd_acquire(inode);
      if (bdev == NULL)
            return -ENOMEM;

      res = do_open(bdev, filp, 0);
      if (res)
            return res;

      if (!(filp->f_flags & O_EXCL) )
            return 0;

      if (!(res = bd_claim(bdev, filp)))
            return 0;

      blkdev_put(bdev);
      return res;
}

static int __blkdev_put(struct block_device *bdev, int for_part)
{
      int ret = 0;
      struct inode *bd_inode = bdev->bd_inode;
      struct gendisk *disk = bdev->bd_disk;
      struct block_device *victim = NULL;

      mutex_lock_nested(&bdev->bd_mutex, for_part);
      lock_kernel();
      if (for_part)
            bdev->bd_part_count--;

      if (!--bdev->bd_openers) {
            sync_blockdev(bdev);
            kill_bdev(bdev);
      }
      if (bdev->bd_contains == bdev) {
            if (disk->fops->release)
                  ret = disk->fops->release(bd_inode, NULL);
      }
      if (!bdev->bd_openers) {
            struct module *owner = disk->fops->owner;

            put_disk(disk);
            module_put(owner);

            if (bdev->bd_contains != bdev) {
                  kobject_put(&bdev->bd_part->kobj);
                  bdev->bd_part = NULL;
            }
            bdev->bd_disk = NULL;
            bdev->bd_inode->i_data.backing_dev_info = &default_backing_dev_info;
            if (bdev != bdev->bd_contains)
                  victim = bdev->bd_contains;
            bdev->bd_contains = NULL;
      }
      unlock_kernel();
      mutex_unlock(&bdev->bd_mutex);
      bdput(bdev);
      if (victim)
            __blkdev_put(victim, 1);
      return ret;
}

int blkdev_put(struct block_device *bdev)
{
      return __blkdev_put(bdev, 0);
}
EXPORT_SYMBOL(blkdev_put);

static int blkdev_close(struct inode * inode, struct file * filp)
{
      struct block_device *bdev = I_BDEV(filp->f_mapping->host);
      if (bdev->bd_holder == filp)
            bd_release(bdev);
      return blkdev_put(bdev);
}

static long block_ioctl(struct file *file, unsigned cmd, unsigned long arg)
{
      return blkdev_ioctl(file->f_mapping->host, file, cmd, arg);
}

const struct address_space_operations def_blk_aops = {
      .readpage   = blkdev_readpage,
      .writepage  = blkdev_writepage,
      .sync_page  = block_sync_page,
      .write_begin      = blkdev_write_begin,
      .write_end  = blkdev_write_end,
      .writepages = generic_writepages,
      .direct_IO  = blkdev_direct_IO,
};

const struct file_operations def_blk_fops = {
      .open       = blkdev_open,
      .release    = blkdev_close,
      .llseek           = block_llseek,
      .read       = do_sync_read,
      .write            = do_sync_write,
      .aio_read   = generic_file_aio_read,
      .aio_write  = generic_file_aio_write_nolock,
      .mmap       = generic_file_mmap,
      .fsync            = block_fsync,
      .unlocked_ioctl   = block_ioctl,
#ifdef CONFIG_COMPAT
      .compat_ioctl     = compat_blkdev_ioctl,
#endif
      .splice_read      = generic_file_splice_read,
      .splice_write     = generic_file_splice_write,
};

int ioctl_by_bdev(struct block_device *bdev, unsigned cmd, unsigned long arg)
{
      int res;
      mm_segment_t old_fs = get_fs();
      set_fs(KERNEL_DS);
      res = blkdev_ioctl(bdev->bd_inode, NULL, cmd, arg);
      set_fs(old_fs);
      return res;
}

EXPORT_SYMBOL(ioctl_by_bdev);

/**
 * lookup_bdev  - lookup a struct block_device by name
 *
 * @path:   special file representing the block device
 *
 * Get a reference to the blockdevice at @path in the current
 * namespace if possible and return it.  Return ERR_PTR(error)
 * otherwise.
 */
struct block_device *lookup_bdev(const char *path)
{
      struct block_device *bdev;
      struct inode *inode;
      struct nameidata nd;
      int error;

      if (!path || !*path)
            return ERR_PTR(-EINVAL);

      error = path_lookup(path, LOOKUP_FOLLOW, &nd);
      if (error)
            return ERR_PTR(error);

      inode = nd.dentry->d_inode;
      error = -ENOTBLK;
      if (!S_ISBLK(inode->i_mode))
            goto fail;
      error = -EACCES;
      if (nd.mnt->mnt_flags & MNT_NODEV)
            goto fail;
      error = -ENOMEM;
      bdev = bd_acquire(inode);
      if (!bdev)
            goto fail;
out:
      path_release(&nd);
      return bdev;
fail:
      bdev = ERR_PTR(error);
      goto out;
}

/**
 * open_bdev_excl  -  open a block device by name and set it up for use
 *
 * @path:   special file representing the block device
 * @flags:  %MS_RDONLY for opening read-only
 * @holder: owner for exclusion
 *
 * Open the blockdevice described by the special file at @path, claim it
 * for the @holder.
 */
struct block_device *open_bdev_excl(const char *path, int flags, void *holder)
{
      struct block_device *bdev;
      mode_t mode = FMODE_READ;
      int error = 0;

      bdev = lookup_bdev(path);
      if (IS_ERR(bdev))
            return bdev;

      if (!(flags & MS_RDONLY))
            mode |= FMODE_WRITE;
      error = blkdev_get(bdev, mode, 0);
      if (error)
            return ERR_PTR(error);
      error = -EACCES;
      if (!(flags & MS_RDONLY) && bdev_read_only(bdev))
            goto blkdev_put;
      error = bd_claim(bdev, holder);
      if (error)
            goto blkdev_put;

      return bdev;
      
blkdev_put:
      blkdev_put(bdev);
      return ERR_PTR(error);
}

EXPORT_SYMBOL(open_bdev_excl);

/**
 * close_bdev_excl  -  release a blockdevice openen by open_bdev_excl()
 *
 * @bdev:   blockdevice to close
 *
 * This is the counterpart to open_bdev_excl().
 */
void close_bdev_excl(struct block_device *bdev)
{
      bd_release(bdev);
      blkdev_put(bdev);
}

EXPORT_SYMBOL(close_bdev_excl);

int __invalidate_device(struct block_device *bdev)
{
      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);
            drop_super(sb);
      }
      invalidate_bdev(bdev);
      return res;
}
EXPORT_SYMBOL(__invalidate_device);

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