[PATCH 4/5] dax: use sb_issue_zerout instead of calling dax_clear_sectors

[Christoph Hellwig]

On Thu, Mar 24, 2016 at 05:17:29PM -0600, Vishal Verma wrote:
> @@ -72,16 +72,7 @@ xfs_zero_extent(
>  	struct xfs_mount *mp = ip->i_mount;
>  	xfs_daddr_t	sector = xfs_fsb_to_db(ip, start_fsb);
>  	sector_t	block = XFS_BB_TO_FSBT(mp, sector);
> -	ssize_t		size = XFS_FSB_TO_B(mp, count_fsb);
>  
> -	if (IS_DAX(VFS_I(ip)))
> -		return dax_clear_sectors(xfs_find_bdev_for_inode(VFS_I(ip)),
> -				sector, size);
> -
> -	/*
> -	 * let the block layer decide on the fastest method of
> -	 * implementing the zeroing.
> -	 */
>  	return sb_issue_zeroout(mp->m_super, block, count_fsb, GFP_NOFS);

While not new: using sb_issue_zeroout in XFS is wrong as it doesn't
account for the RT device.  We need the xfs_find_bdev_for_inode and
call blkdev_issue_zeroout directly with the bdev it returned.