#include <linux/export.h>
  #include <linux/fs.h>
  #include <linux/fs_stack.h>
  
  /* does _NOT_ require i_mutex to be held.
   *
   * This function cannot be inlined since i_size_{read,write} is rather
   * heavy-weight on 32-bit systems
   */
  void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
  {
  	loff_t i_size;
  	blkcnt_t i_blocks;
  
  	/*
  	 * i_size_read() includes its own seqlocking and protection from
  	 * preemption (see include/linux/fs.h): we need nothing extra for
  	 * that here, and prefer to avoid nesting locks than attempt to keep
  	 * i_size and i_blocks in sync together.
  	 */
  	i_size = i_size_read(src);
  
  	/*
  	 * But if CONFIG_LBDAF (on 32-bit), we ought to make an effort to
  	 * keep the two halves of i_blocks in sync despite SMP or PREEMPT -
  	 * though stat's generic_fillattr() doesn't bother, and we won't be
  	 * applying quotas (where i_blocks does become important) at the
  	 * upper level.
  	 *
  	 * We don't actually know what locking is used at the lower level;
  	 * but if it's a filesystem that supports quotas, it will be using
  	 * i_lock as in inode_add_bytes().
  	 */
  	if (sizeof(i_blocks) > sizeof(long))
  		spin_lock(&src->i_lock);
  	i_blocks = src->i_blocks;
  	if (sizeof(i_blocks) > sizeof(long))
  		spin_unlock(&src->i_lock);
  
  	/*
  	 * If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for
  	 * fsstack_copy_inode_size() to hold some lock around
  	 * i_size_write(), otherwise i_size_read() may spin forever (see
  	 * include/linux/fs.h).  We don't necessarily hold i_mutex when this
  	 * is called, so take i_lock for that case.
  	 *
  	 * And if CONFIG_LBADF (on 32-bit), continue our effort to keep the
  	 * two halves of i_blocks in sync despite SMP or PREEMPT: use i_lock
  	 * for that case too, and do both at once by combining the tests.
  	 *
  	 * There is none of this locking overhead in the 64-bit case.
  	 */
  	if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
  		spin_lock(&dst->i_lock);
  	i_size_write(dst, i_size);
  	dst->i_blocks = i_blocks;
  	if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
  		spin_unlock(&dst->i_lock);
  }
  EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
  
  /* copy all attributes */
  void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
  {
  	dest->i_mode = src->i_mode;
  	dest->i_uid = src->i_uid;
  	dest->i_gid = src->i_gid;
  	dest->i_rdev = src->i_rdev;
  	dest->i_atime = src->i_atime;
  	dest->i_mtime = src->i_mtime;
  	dest->i_ctime = src->i_ctime;
  	dest->i_blkbits = src->i_blkbits;
  	dest->i_flags = src->i_flags;
  	set_nlink(dest, src->i_nlink);
  }
  EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);