block: get rid of bio_rw and READA

These two are confusing leftover of the old world order, combining
values of the REQ_OP_ and REQ_ namespaces.  For callers that don't
special case we mostly just replace bi_rw with bio_data_dir or
op_is_write, except for the few cases where a switch over the REQ_OP_
values makes more sense.  Any check for READA is replaced with an
explicit check for REQ_RAHEAD.  Also remove the READA alias for
REQ_RAHEAD.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/md/dm-snap.c

@@ -1696,7 +1696,8 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)
 	 * to copy an exception */
 	down_write(&s->lock);
 
-	if (!s->valid || (unlikely(s->snapshot_overflowed) && bio_rw(bio) == WRITE)) {
+	if (!s->valid || (unlikely(s->snapshot_overflowed) &&
+	    bio_data_dir(bio) == WRITE)) {
 		r = -EIO;
 		goto out_unlock;
 	}
@@ -1713,7 +1714,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)
 	 * flags so we should only get this if we are
 	 * writeable.
 	 */
-	if (bio_rw(bio) == WRITE) {
+	if (bio_data_dir(bio) == WRITE) {
 		pe = __lookup_pending_exception(s, chunk);
 		if (!pe) {
 			up_write(&s->lock);
@@ -1819,7 +1820,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)
 	e = dm_lookup_exception(&s->complete, chunk);
 	if (e) {
 		/* Queue writes overlapping with chunks being merged */
-		if (bio_rw(bio) == WRITE &&
+		if (bio_data_dir(bio) == WRITE &&
 		    chunk >= s->first_merging_chunk &&
 		    chunk < (s->first_merging_chunk +
 			     s->num_merging_chunks)) {
@@ -1831,7 +1832,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)
 
 		remap_exception(s, e, bio, chunk);
 
-		if (bio_rw(bio) == WRITE)
+		if (bio_data_dir(bio) == WRITE)
 			track_chunk(s, bio, chunk);
 		goto out_unlock;
 	}
@@ -1839,7 +1840,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)
 redirect_to_origin:
 	bio->bi_bdev = s->origin->bdev;
 
-	if (bio_rw(bio) == WRITE) {
+	if (bio_data_dir(bio) == WRITE) {
 		up_write(&s->lock);
 		return do_origin(s->origin, bio);
 	}
@@ -2288,7 +2289,7 @@ static int origin_map(struct dm_target *ti, struct bio *bio)
 	if (unlikely(bio->bi_rw & REQ_PREFLUSH))
 		return DM_MAPIO_REMAPPED;
 
-	if (bio_rw(bio) != WRITE)
+	if (bio_data_dir(bio) != WRITE)
 		return DM_MAPIO_REMAPPED;
 
 	available_sectors = o->split_boundary -