FreeBSD/Linux Kernel Cross Reference
sys/fs/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/device_cgroup.h>
    #include <linux/highmem.h>
    #include <linux/blkdev.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/uio.h>
    #include <linux/namei.h>
    #include <linux/log2.h>
    #include <linux/cleancache.h>
    #include <asm/uaccess.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);
    }
    
    inline struct block_device *I_BDEV(struct inode *inode)
    {
            return &BDEV_I(inode)->bdev;
    }
    EXPORT_SYMBOL(I_BDEV);
    
    /*
     * Move the inode from its current bdi to a new bdi. If the inode is dirty we
     * need to move it onto the dirty list of @dst so that the inode is always on
     * the right list.
     */
    static void bdev_inode_switch_bdi(struct inode *inode,
                            struct backing_dev_info *dst)
    {
            struct backing_dev_info *old = inode->i_data.backing_dev_info;
    
            if (unlikely(dst == old))               /* deadlock avoidance */
                    return;
            bdi_lock_two(&old->wb, &dst->wb);
            spin_lock(&inode->i_lock);
            inode->i_data.backing_dev_info = dst;
            if (inode->i_state & I_DIRTY)
                    list_move(&inode->i_wb_list, &dst->wb.b_dirty);
            spin_unlock(&inode->i_lock);
            spin_unlock(&old->wb.list_lock);
            spin_unlock(&dst->wb.list_lock);
    }
    
    /* Kill _all_ buffers and pagecache , dirty or not.. */
    void kill_bdev(struct block_device *bdev)
    {
            struct address_space *mapping = bdev->bd_inode->i_mapping;
    
            if (mapping->nrpages == 0)
                    return;
    
            invalidate_bh_lrus();
            truncate_inode_pages(mapping, 0);
    }       
    EXPORT_SYMBOL(kill_bdev);
    
    /* 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 == 0)
                    return;
    
            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);
   
   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_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_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 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(rw, iocb, inode, I_BDEV(inode), iov, offset,
                                       nr_segs, blkdev_get_block, NULL, NULL, 0);
   }
   
   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);
                   drop_super(sb);
                   mutex_unlock(&bdev->bd_fsfreeze_mutex);
                   return sb;
           }
   
           sb = get_active_super(bdev);
           if (!sb)
                   goto out;
           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;
   
           error = thaw_super(sb);
           if (error) {
                   bdev->bd_fsfreeze_count++;
                   mutex_unlock(&bdev->bd_fsfreeze_mutex);
                   return error;
           }
   out:
           mutex_unlock(&bdev->bd_fsfreeze_mutex);
           return 0;
   }
   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 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);
           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 whence)
   {
           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);
   
           retval = -EINVAL;
           switch (whence) {
                   case SEEK_END:
                           offset += size;
                           break;
                   case SEEK_CUR:
                           offset += file->f_pos;
                   case SEEK_SET:
                           break;
                   default:
                           goto out;
           }
           if (offset >= 0 && offset <= size) {
                   if (offset != file->f_pos) {
                           file->f_pos = offset;
                   }
                   retval = offset;
           }
   out:
           mutex_unlock(&bd_inode->i_mutex);
           return retval;
   }
           
   int blkdev_fsync(struct file *filp, loff_t start, loff_t end, int datasync)
   {
           struct inode *bd_inode = filp->f_mapping->host;
           struct block_device *bdev = I_BDEV(bd_inode);
           int error;
           
           error = filemap_write_and_wait_range(filp->f_mapping, 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, NULL);
           if (error == -EOPNOTSUPP)
                   error = 0;
   
           return error;
   }
   EXPORT_SYMBOL(blkdev_fsync);
   
   /*
    * 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_i_callback(struct rcu_head *head)
   {
           struct inode *inode = container_of(head, struct inode, i_rcu);
           struct bdev_inode *bdi = BDEV_I(inode);
   
           kmem_cache_free(bdev_cachep, bdi);
   }
   
   static void bdev_destroy_inode(struct inode *inode)
   {
           call_rcu(&inode->i_rcu, bdev_i_callback);
   }
   
   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);
           INIT_LIST_HEAD(&bdev->bd_inodes);
           INIT_LIST_HEAD(&bdev->bd_list);
   #ifdef CONFIG_SYSFS
           INIT_LIST_HEAD(&bdev->bd_holder_disks);
   #endif
           inode_init_once(&ei->vfs_inode);
           /* Initialize mutex for freeze. */
           mutex_init(&bdev->bd_fsfreeze_mutex);
   }
   
   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_evict_inode(struct inode *inode)
   {
           struct block_device *bdev = &BDEV_I(inode)->bdev;
           struct list_head *p;
           truncate_inode_pages(&inode->i_data, 0);
           invalidate_inode_buffers(inode); /* is it needed here? */
           clear_inode(inode);
           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,
           .evict_inode = bdev_evict_inode,
   };
   
   static struct dentry *bd_mount(struct file_system_type *fs_type,
           int flags, const char *dev_name, void *data)
   {
           return mount_pseudo(fs_type, "bdev:", &bdev_sops, NULL, BDEVFS_MAGIC);
   }
   
   static struct file_system_type bd_type = {
           .name           = "bdev",
           .mount          = bd_mount,
           .kill_sb        = kill_anon_super,
   };
   
   static struct super_block *blockdev_superblock __read_mostly;
   
   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_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 LIST_HEAD(all_bdevs);
   
   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) {
                   bdev->bd_contains = NULL;
                   bdev->bd_super = 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);
   
   /**
    * 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;
   }
   
   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) {
                   ihold(bdev->bd_inode);
                   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 reference to bd_inode,
                            * and it's released in clear_inode() of inode.
                            * So, we can access it via ->i_mapping always
                            * without igrab().
                            */
                           ihold(bdev->bd_inode);
                           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;
   }
   
   static inline int sb_is_blkdev_sb(struct super_block *sb)
   {
           return sb == blockdev_superblock;
   }
   
   /* 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 (!sb_is_blkdev_sb(inode->i_sb))
                           bdev = inode->i_bdev;
                   __bd_forget(inode);
           }
           spin_unlock(&bdev_lock);
   
           if (bdev)
                   iput(bdev->bd_inode);
   }
   
   /**
    * 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 (bdev->bd_contains == 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 - prepare to claim a block device
    * @bdev: block device of interest
    * @whole: the whole device containing @bdev, may equal @bdev
    * @holder: holder trying to claim @bdev
    *
    * Prepare to claim @bdev.  This function fails if @bdev is already
    * claimed by another holder and waits if another claiming is in
    * progress.  This function doesn't actually claim.  On successful
    * return, the caller has ownership of bd_claiming and bd_holder[s].
    *
    * CONTEXT:
    * spin_lock(&bdev_lock).  Might release bdev_lock, sleep and regrab
    * it multiple times.
    *
    * RETURNS:
    * 0 if @bdev can be claimed, -EBUSY otherwise.
    */
   static int bd_prepare_to_claim(struct block_device *bdev,
                                  struct block_device *whole, void *holder)
   {
   retry:
           /* if someone else claimed, fail */
           if (!bd_may_claim(bdev, whole, holder))
                   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);
                   spin_lock(&bdev_lock);
                   goto retry;
           }
   
           /* yay, all mine */
           return 0;
   }
   
   /**
    * bd_start_claiming - start claiming a block device
    * @bdev: block device of interest
    * @holder: holder trying to claim @bdev
    *
    * @bdev is about to be opened exclusively.  Check @bdev can be opened
    * exclusively and mark that an exclusive open is in progress.  Each
    * successful call to this function must be matched with a call to
    * either bd_finish_claiming() or bd_abort_claiming() (which do not
    * fail).
    *
    * This function is used to gain exclusive access to the block device
    * without actually causing other exclusive open attempts to fail. It
    * should be used when the open sequence itself requires exclusive
    * access but may subsequently fail.
    *
    * CONTEXT:
    * Might sleep.
    *
    * RETURNS:
    * Pointer to the block device containing @bdev on success, ERR_PTR()
    * value on failure.
    */
   static struct block_device *bd_start_claiming(struct block_device *bdev,
                                                 void *holder)
   {
           struct gendisk *disk;
           struct block_device *whole;
           int partno, err;
   
           might_sleep();
   
           /*
            * @bdev might not have been initialized properly yet, look up
            * and grab the outer block device the hard way.
            */
           disk = get_gendisk(bdev->bd_dev, &partno);
           if (!disk)
                   return ERR_PTR(-ENXIO);
   
           /*
            * Normally, @bdev should equal what's returned from bdget_disk()
            * if partno is 0; however, some drivers (floppy) use multiple
            * bdev's for the same physical device and @bdev may be one of the
            * aliases.  Keep @bdev if partno is 0.  This means claimer
            * tracking is broken for those devices but it has always been that
            * way.
            */
           if (partno)
                   whole = bdget_disk(disk, 0);
           else
                   whole = bdgrab(bdev);
   
           module_put(disk->fops->owner);
           put_disk(disk);
           if (!whole)
                   return ERR_PTR(-ENOMEM);
   
           /* prepare to claim, if successful, mark claiming in progress */
           spin_lock(&bdev_lock);
   
           err = bd_prepare_to_claim(bdev, whole, holder);
           if (err == 0) {
                   whole->bd_claiming = holder;
                   spin_unlock(&bdev_lock);
                   return whole;
           } else {
                   spin_unlock(&bdev_lock);
                   bdput(whole);
                   return ERR_PTR(err);
           }
   }
   
   #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
   
   /**
    * flush_disk - invalidates all buffer-cache entries on a disk
    *
    * @bdev:      struct block device to be flushed
    * @kill_dirty: flag to guide handling of dirty inodes
    *
    * Invalidates all buffer-cache entries on a disk. It should be called
    * when a disk has been changed -- either by a media change or online
    * resize.
    */
   static void flush_disk(struct block_device *bdev, bool kill_dirty)
   {
           if (__invalidate_device(bdev, kill_dirty)) {
                   char name[BDEVNAME_SIZE] = "";
   
                   if (bdev->bd_disk)
                           disk_name(bdev->bd_disk, 0, name);
                   printk(KERN_WARNING "VFS: busy inodes on changed media or "
                          "resized disk %s\n", name);
           }
   
           if (!bdev->bd_disk)
                   return;
           if (disk_part_scan_enabled(bdev->bd_disk))
                   bdev->bd_invalidated = 1;
   }
   
   /**
    * check_disk_size_change - checks for disk size change and adjusts bdev size.
    * @disk: struct gendisk to check
    * @bdev: struct bdev to adjust.
    *
    * This routine checks to see if the bdev size does not match the disk size
    * and adjusts it if it differs.
    */
   void check_disk_size_change(struct gendisk *disk, struct block_device *bdev)
   {
           loff_t disk_size, bdev_size;
   
           disk_size = (loff_t)get_capacity(disk) << 9;
           bdev_size = i_size_read(bdev->bd_inode);
           if (disk_size != bdev_size) {
                   char name[BDEVNAME_SIZE];
   
                   disk_name(disk, 0, name);
                   printk(KERN_INFO
                          "%s: detected capacity change from %lld to %lld\n",
                          name, bdev_size, disk_size);
                   i_size_write(bdev->bd_inode, disk_size);
                   flush_disk(bdev, false);
           }
   }
   EXPORT_SYMBOL(check_disk_size_change);
   
   /**
    * revalidate_disk - wrapper for lower-level driver's revalidate_disk call-back
    * @disk: struct gendisk to be revalidated
    *
    * This routine is a wrapper for lower-level driver's revalidate_disk
    * call-backs.  It is used to do common pre and post operations needed
    * for all revalidate_disk operations.
    */
   int revalidate_disk(struct gendisk *disk)
   {
           struct block_device *bdev;
           int ret = 0;
   
           if (disk->fops->revalidate_disk)
                   ret = disk->fops->revalidate_disk(disk);
   
           bdev = bdget_disk(disk, 0);
           if (!bdev)
                   return ret;
   
           mutex_lock(&bdev->bd_mutex);
           check_disk_size_change(disk, bdev);
           mutex_unlock(&bdev->bd_mutex);
           bdput(bdev);
           return ret;
  }
  EXPORT_SYMBOL(revalidate_disk);
  
  /*
   * 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;
          const struct block_device_operations *bdops = disk->fops;
          unsigned int events;
  
          events = disk_clear_events(disk, DISK_EVENT_MEDIA_CHANGE |
                                     DISK_EVENT_EJECT_REQUEST);
          if (!(events & DISK_EVENT_MEDIA_CHANGE))
                  return 0;
  
          flush_disk(bdev, true);
          if (bdops->revalidate_disk)
                  bdops->revalidate_disk(bdev->bd_disk);
          return 1;
  }
  
  EXPORT_SYMBOL(check_disk_change);
  
  void bd_set_size(struct block_device *bdev, loff_t size)
  {
          unsigned bsize = bdev_logical_block_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_put(struct block_device *bdev, fmode_t mode, int for_part);
  
  /*
   * 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, int for_part)
  {
          struct gendisk *disk;
          struct module *owner;
          int ret;
          int partno;
          int perm = 0;
  
          if (mode & FMODE_READ)
                  perm |= MAY_READ;
          if (mode & FMODE_WRITE)
                  perm |= MAY_WRITE;
          /*
           * hooks: /n/, see "layering violations".
           */
          if (!for_part) {
                  ret = devcgroup_inode_permission(bdev->bd_inode, perm);
                  if (ret != 0) {
                          bdput(bdev);
                          return ret;
                  }
          }
  
   restart:
  
          ret = -ENXIO;
          disk = get_gendisk(bdev->bd_dev, &partno);
          if (!disk)
                  goto out;
          owner = disk->fops->owner;
  
          disk_block_events(disk);
          mutex_lock_nested(&bdev->bd_mutex, for_part);
          if (!bdev->bd_openers) {
                  bdev->bd_disk = disk;
                  bdev->bd_queue = disk->queue;
                  bdev->bd_contains = bdev;
                  if (!partno) {
                          struct backing_dev_info *bdi;
  
                          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 (ret == -ERESTARTSYS) {
                                          /* Lost a race with 'disk' being
                                           * deleted, try again.
                                           * See md.c
                                           */
                                          disk_put_part(bdev->bd_part);
                                          bdev->bd_part = NULL;
                                          bdev->bd_disk = NULL;
                                          bdev->bd_queue = NULL;
                                          mutex_unlock(&bdev->bd_mutex);
                                          disk_unblock_events(disk);
                                          put_disk(disk);
                                          module_put(owner);
                                          goto restart;
                                  }
                          }
  
                          if (!ret && !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_inode_switch_bdi(bdev->bd_inode, bdi);
                          }
  
                          /*
                           * 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 (bdev->bd_invalidated) {
                                  if (!ret)
                                          rescan_partitions(disk, bdev);
                                  else if (ret == -ENOMEDIUM)
                                          invalidate_partitions(disk, bdev);
                          }
                          if (ret)
                                  goto out_clear;
                  } else {
                          struct block_device *whole;
                          whole = bdget_disk(disk, 0);
                          ret = -ENOMEM;
                          if (!whole)
                                  goto out_clear;
                          BUG_ON(for_part);
                          ret = __blkdev_get(whole, mode, 1);
                          if (ret)
                                  goto out_clear;
                          bdev->bd_contains = whole;
                          bdev_inode_switch_bdi(bdev->bd_inode,
                                  whole->bd_inode->i_data.backing_dev_info);
                          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_size(bdev, (loff_t)bdev->bd_part->nr_sects << 9);
                  }
          } 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 (bdev->bd_invalidated) {
                                  if (!ret)
                                          rescan_partitions(bdev->bd_disk, bdev);
                                  else if (ret == -ENOMEDIUM)
                                          invalidate_partitions(bdev->bd_disk, bdev);
                          }
                          if (ret)
                                  goto out_unlock_bdev;
                  }
                  /* only one opener holds refs to the module and disk */
                  put_disk(disk);
                  module_put(owner);
          }
          bdev->bd_openers++;
          if (for_part)
                  bdev->bd_part_count++;
          mutex_unlock(&bdev->bd_mutex);
          disk_unblock_events(disk);
          return 0;
  
   out_clear:
          disk_put_part(bdev->bd_part);
          bdev->bd_disk = NULL;
          bdev->bd_part = NULL;
          bdev->bd_queue = NULL;
          bdev_inode_switch_bdi(bdev->bd_inode, &default_backing_dev_info);
          if (bdev != bdev->bd_contains)
                  __blkdev_put(bdev->bd_contains, mode, 1);
          bdev->bd_contains = NULL;
   out_unlock_bdev:
          mutex_unlock(&bdev->bd_mutex);
          disk_unblock_events(disk);
          put_disk(disk);
          module_put(owner);
   out:
          bdput(bdev);
  
          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.
   */
  int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
  {
          struct block_device *whole = NULL;
          int res;
  
          WARN_ON_ONCE((mode & FMODE_EXCL) && !holder);
  
          if ((mode & FMODE_EXCL) && holder) {
                  whole = bd_start_claiming(bdev, holder);
                  if (IS_ERR(whole)) {
                          bdput(bdev);
                          return PTR_ERR(whole);
                  }
          }
  
          res = __blkdev_get(bdev, mode, 0);
  
          if (whole) {
                  struct gendisk *disk = whole->bd_disk;
  
                  /* finish claiming */
                  mutex_lock(&bdev->bd_mutex);
                  spin_lock(&bdev_lock);
  
                  if (!res) {
                          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;
                  }
  
                  /* tell others that we're done */
                  BUG_ON(whole->bd_claiming != holder);
                  whole->bd_claiming = NULL;
                  wake_up_bit(&whole->bd_claiming, 0);
  
                  spin_unlock(&bdev_lock);
  
                  /*
                   * 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 (!res && (mode & FMODE_WRITE) && !bdev->bd_write_holder &&
                      (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
                          bdev->bd_write_holder = true;
                          disk_block_events(disk);
                  }
  
                  mutex_unlock(&bdev->bd_mutex);
                  bdput(whole);
          }
  
          return res;
  }
  EXPORT_SYMBOL(blkdev_get);
  
  /**
   * 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;
  
          /*
           * 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;
  
          if (filp->f_flags & O_NDELAY)
                  filp->f_mode |= FMODE_NDELAY;
          if (filp->f_flags & O_EXCL)
                  filp->f_mode |= FMODE_EXCL;
          if ((filp->f_flags & O_ACCMODE) == 3)
                  filp->f_mode |= FMODE_WRITE_IOCTL;
  
          bdev = bd_acquire(inode);
          if (bdev == NULL)
                  return -ENOMEM;
  
          filp->f_mapping = bdev->bd_inode->i_mapping;
  
          return blkdev_get(bdev, filp->f_mode, filp);
  }
  
  static int __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
  {
          int ret = 0;
          struct gendisk *disk = bdev->bd_disk;
          struct block_device *victim = NULL;
  
          mutex_lock_nested(&bdev->bd_mutex, for_part);
          if (for_part)
                  bdev->bd_part_count--;
  
          if (!--bdev->bd_openers) {
                  WARN_ON_ONCE(bdev->bd_holders);
                  sync_blockdev(bdev);
                  kill_bdev(bdev);
                  /* ->release can cause the old bdi to disappear,
                   * so must switch it out first
                   */
                  bdev_inode_switch_bdi(bdev->bd_inode,
                                          &default_backing_dev_info);
          }
          if (bdev->bd_contains == bdev) {
                  if (disk->fops->release)
                          ret = disk->fops->release(disk, mode);
          }
          if (!bdev->bd_openers) {
                  struct module *owner = disk->fops->owner;
  
                  disk_put_part(bdev->bd_part);
                  bdev->bd_part = NULL;
                  bdev->bd_disk = NULL;
                  if (bdev != bdev->bd_contains)
                          victim = bdev->bd_contains;
                  bdev->bd_contains = NULL;
  
                  put_disk(disk);
                  module_put(owner);
          }
          mutex_unlock(&bdev->bd_mutex);
          bdput(bdev);
          if (victim)
                  __blkdev_put(victim, mode, 1);
          return ret;
  }
  
  int blkdev_put(struct block_device *bdev, fmode_t mode)
  {
          mutex_lock(&bdev->bd_mutex);
  
          if (mode & FMODE_EXCL) {
                  bool bdev_free;
  
                  /*
                   * Release a claim on the device.  The holder fields
                   * are protected with bdev_lock.  bd_mutex is to
                   * synchronize disk_holder unlinking.
                   */
                  spin_lock(&bdev_lock);
  
                  WARN_ON_ONCE(--bdev->bd_holders < 0);
                  WARN_ON_ONCE(--bdev->bd_contains->bd_holders < 0);
  
                  /* bd_contains might point to self, check in a separate step */
                  if ((bdev_free = !bdev->bd_holders))
                          bdev->bd_holder = NULL;
                  if (!bdev->bd_contains->bd_holders)
                          bdev->bd_contains->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(bdev->bd_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(bdev->bd_disk, DISK_EVENT_MEDIA_CHANGE);
  
          mutex_unlock(&bdev->bd_mutex);
  
          return __blkdev_put(bdev, mode, 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);
  
          return blkdev_put(bdev, filp->f_mode);
  }
  
  static long block_ioctl(struct file *file, unsigned cmd, unsigned long arg)
  {
          struct block_device *bdev = I_BDEV(file->f_mapping->host);
          fmode_t mode = file->f_mode;
  
          /*
           * O_NDELAY can be altered using fcntl(.., F_SETFL, ..), so we have
           * to updated it before every ioctl.
           */
          if (file->f_flags & O_NDELAY)
                  mode |= FMODE_NDELAY;
          else
                  mode &= ~FMODE_NDELAY;
  
          return blkdev_ioctl(bdev, mode, cmd, arg);
  }
  
  /*
   * Write data to the block device.  Only intended for the block device itself
   * and the raw driver which basically is a fake block device.
   *
   * Does not take i_mutex for the write and thus is not for general purpose
   * use.
   */
  ssize_t blkdev_aio_write(struct kiocb *iocb, const struct iovec *iov,
                           unsigned long nr_segs, loff_t pos)
  {
          struct file *file = iocb->ki_filp;
          struct blk_plug plug;
          ssize_t ret;
  
          BUG_ON(iocb->ki_pos != pos);
  
          blk_start_plug(&plug);
          ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
          if (ret > 0 || ret == -EIOCBQUEUED) {
                  ssize_t err;
  
                  err = generic_write_sync(file, pos, ret);
                  if (err < 0 && ret > 0)
                          ret = err;
          }
          blk_finish_plug(&plug);
          return ret;
  }
  EXPORT_SYMBOL_GPL(blkdev_aio_write);
  
  static ssize_t blkdev_aio_read(struct kiocb *iocb, const struct iovec *iov,
                           unsigned long nr_segs, loff_t pos)
  {
          struct file *file = iocb->ki_filp;
          struct inode *bd_inode = file->f_mapping->host;
          loff_t size = i_size_read(bd_inode);
  
          if (pos >= size)
                  return 0;
  
          size -= pos;
          if (size < INT_MAX)
                  nr_segs = iov_shorten((struct iovec *)iov, nr_segs, size);
          return generic_file_aio_read(iocb, iov, nr_segs, pos);
  }
  
  /*
   * Try to release a page associated with block device when the system
   * is under memory pressure.
   */
  static int blkdev_releasepage(struct page *page, gfp_t wait)
  {
          struct super_block *super = BDEV_I(page->mapping->host)->bdev.bd_super;
  
          if (super && super->s_op->bdev_try_to_free_page)
                  return super->s_op->bdev_try_to_free_page(super, page, wait);
  
          return try_to_free_buffers(page);
  }
  
  static const struct address_space_operations def_blk_aops = {
          .readpage       = blkdev_readpage,
          .writepage      = blkdev_writepage,
          .write_begin    = blkdev_write_begin,
          .write_end      = blkdev_write_end,
          .writepages     = generic_writepages,
          .releasepage    = blkdev_releasepage,
          .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       = blkdev_aio_read,
          .aio_write      = blkdev_aio_write,
          .mmap           = generic_file_mmap,
          .fsync          = blkdev_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, 0, cmd, arg);
          set_fs(old_fs);
          return res;
  }
  
  EXPORT_SYMBOL(ioctl_by_bdev);
  
  /**
   * lookup_bdev  - lookup a struct block_device by name
   * @pathname:   special file representing the block device
   *
   * Get a reference to the blockdevice at @pathname in the current
   * namespace if possible and return it.  Return ERR_PTR(error)
   * otherwise.
   */
  struct block_device *lookup_bdev(const char *pathname)
  {
          struct block_device *bdev;
          struct inode *inode;
          struct path path;
          int error;
  
          if (!pathname || !*pathname)
                  return ERR_PTR(-EINVAL);
  
          error = kern_path(pathname, LOOKUP_FOLLOW, &path);
          if (error)
                  return ERR_PTR(error);
  
          inode = path.dentry->d_inode;
          error = -ENOTBLK;
          if (!S_ISBLK(inode->i_mode))
                  goto fail;
          error = -EACCES;
          if (path.mnt->mnt_flags & MNT_NODEV)
                  goto fail;
          error = -ENOMEM;
          bdev = bd_acquire(inode);
          if (!bdev)
                  goto fail;
  out:
          path_put(&path);
          return bdev;
  fail:
          bdev = ERR_PTR(error);
          goto out;
  }
  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(&inode_sb_list_lock);
          list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list) {
                  struct address_space *mapping = inode->i_mapping;
  
                  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(&inode_sb_list_lock);
                  /*
                   * We hold a reference to 'inode' so it couldn't have been
                   * removed from s_inodes list while we dropped the
                   * inode_sb_list_lock.  We cannot iput the inode now as we can
                   * be holding the last reference and we cannot iput it under
                   * inode_sb_list_lock. So we keep the reference and iput it
                   * later.
                   */
                  iput(old_inode);
                  old_inode = inode;
  
                  func(I_BDEV(inode), arg);
  
                  spin_lock(&inode_sb_list_lock);
          }
          spin_unlock(&inode_sb_list_lock);
          iput(old_inode);
  }

Cache object: dbfbee1db9af95c10164f926d8790fa7