Add a private pointer to struct iomap to allow filesystems to pass data
from iomap_begin to iomap_end.  Will be used by gfs2 for passing on the
on-disk inode buffer head.
Signed-off-by: NAndreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>