iomap: Switch from blkno to disk offset

Replace iomap->blkno, the sector number, with iomap->addr, the disk
offset in bytes.  For invalid disk offsets, use the special value
IOMAP_NULL_ADDR instead of IOMAP_NULL_BLOCK.

This allows to use iomap for mappings which are not block aligned, such
as inline data on ext4.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>  # iomap, xfs
Reviewed-by: Jan Kara <jack@suse.cz>

fs/ext4/inode.c

@@ -3472,7 +3472,7 @@ retry:
 
 	if (ret == 0) {
 		iomap->type = IOMAP_HOLE;
-		iomap->blkno = IOMAP_NULL_BLOCK;
+		iomap->addr = IOMAP_NULL_ADDR;
 		iomap->length = (u64)map.m_len << blkbits;
 	} else {
 		if (map.m_flags & EXT4_MAP_MAPPED) {
@@ -3483,7 +3483,7 @@ retry:
 			WARN_ON_ONCE(1);
 			return -EIO;
 		}
-		iomap->blkno = (sector_t)map.m_pblk << (blkbits - 9);
+		iomap->addr = (u64)map.m_pblk << blkbits;
 		iomap->length = (u64)map.m_len << blkbits;
 	}