/*
   * linux/fs/ext4/truncate.h
   *
   * Common inline functions needed for truncate support
   */
  
  /*
   * Truncate blocks that were not used by write. We have to truncate the
   * pagecache as well so that corresponding buffers get properly unmapped.
   */
  static inline void ext4_truncate_failed_write(struct inode *inode)
  {

  	down_write(&EXT4_I(inode)->i_mmap_sem);

  	truncate_inode_pages(inode->i_mapping, inode->i_size);
  	ext4_truncate(inode);

  	up_write(&EXT4_I(inode)->i_mmap_sem);

  }
  
  /*
   * Work out how many blocks we need to proceed with the next chunk of a
   * truncate transaction.
   */
  static inline unsigned long ext4_blocks_for_truncate(struct inode *inode)
  {
  	ext4_lblk_t needed;
  
  	needed = inode->i_blocks >> (inode->i_sb->s_blocksize_bits - 9);
  
  	/* Give ourselves just enough room to cope with inodes in which
  	 * i_blocks is corrupt: we've seen disk corruptions in the past
  	 * which resulted in random data in an inode which looked enough
  	 * like a regular file for ext4 to try to delete it.  Things
  	 * will go a bit crazy if that happens, but at least we should
  	 * try not to panic the whole kernel. */
  	if (needed < 2)
  		needed = 2;
  
  	/* But we need to bound the transaction so we don't overflow the
  	 * journal. */
  	if (needed > EXT4_MAX_TRANS_DATA)
  		needed = EXT4_MAX_TRANS_DATA;
  
  	return EXT4_DATA_TRANS_BLOCKS(inode->i_sb) + needed;
  }