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>

fs/gfs2/bmap.c

@@ -285,7 +285,8 @@ static void gfs2_metapath_ra(struct gfs2_glock *gl,
 		if (trylock_buffer(rabh)) {
 			if (!buffer_uptodate(rabh)) {
 				rabh->b_end_io = end_buffer_read_sync;
-				submit_bh(REQ_OP_READ, READA | REQ_META, rabh);
+				submit_bh(REQ_OP_READ, REQ_RAHEAD | REQ_META,
+						rabh);
 				continue;
 			}
 			unlock_buffer(rabh);

fs/gfs2/dir.c

@@ -1513,7 +1513,7 @@ static void gfs2_dir_readahead(struct inode *inode, unsigned hsize, u32 index,
 				continue;
 			}
 			bh->b_end_io = end_buffer_read_sync;
-			submit_bh(REQ_OP_READ, READA | REQ_META, bh);
+			submit_bh(REQ_OP_READ, REQ_RAHEAD | REQ_META, bh);
 			continue;
 		}
 		brelse(bh);

fs/gfs2/meta_io.c

@@ -459,7 +459,7 @@ struct buffer_head *gfs2_meta_ra(struct gfs2_glock *gl, u64 dblock, u32 extlen)
 		bh = gfs2_getbuf(gl, dblock, CREATE);
 
 		if (!buffer_uptodate(bh) && !buffer_locked(bh))
-			ll_rw_block(REQ_OP_READ, READA | REQ_META, 1, &bh);
+			ll_rw_block(REQ_OP_READ, REQ_RAHEAD | REQ_META, 1, &bh);
 		brelse(bh);
 		dblock++;
 		extlen--;