__gfs2_iomap_get
ret = __gfs2_iomap_get(inode, iomap->offset,
ret = __gfs2_iomap_get(inode, pos, length, flags, iomap, &mp);
ret = __gfs2_iomap_get(inode, pos, length, 0, iomap, &mp);
ret = __gfs2_iomap_get(inode, pos, length, IOMAP_WRITE, iomap, &mp);