xfs: simplify sector number calculation in xfs_zero_extent

xfs_zero_extent does some really odd gymnstics to calculate the block
layer sectors numbers passed to blkdev_issue_zeroout.  This is because it
used to call sb_issue_zeroout and the calculations in that helper got
open coded here in the rather misleadingly named commit 3dc2916
("dax: use sb_issue_zerout instead of calling dax_clear_sectors").

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

Author: Christoph Hellwig

fs/xfs/xfs_bmap_util.c

@@ -47,26 +47,17 @@ xfs_fsb_to_db(struct xfs_inode *ip, xfs_fsblock_t fsb)
 
 /*
  * Routine to zero an extent on disk allocated to the specific inode.
- *
- * The VFS functions take a linearised filesystem block offset, so we have to
- * convert the sparse xfs fsb to the right format first.
- * VFS types are real funky, too.
  */
 int
 xfs_zero_extent(
 	struct xfs_inode	*ip,
 	xfs_fsblock_t		start_fsb,
 	xfs_off_t		count_fsb)
 {
-	struct xfs_mount	*mp = ip->i_mount;
-	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
-	xfs_daddr_t		sector = xfs_fsb_to_db(ip, start_fsb);
-	sector_t		block = XFS_BB_TO_FSBT(mp, sector);
-
-	return blkdev_issue_zeroout(target->bt_bdev,
-		block << (mp->m_super->s_blocksize_bits - 9),
-		count_fsb << (mp->m_super->s_blocksize_bits - 9),
-		GFP_KERNEL, 0);
+	return blkdev_issue_zeroout(xfs_inode_buftarg(ip)->bt_bdev,
+			xfs_fsb_to_db(ip, start_fsb),
+			XFS_FSB_TO_BB(ip->i_mount, count_fsb),
+			GFP_KERNEL, 0);
 }
 
 /*