xen-blkback: Use the enum req_op and blk_opf_t types

Improve static type checking by using the enum req_op type for request
operations and the new blk_opf_t type for request flags.
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220714180729.1065367-18-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/xen-blkback/blkback.c

@@ -442,7 +442,7 @@ static void free_req(struct xen_blkif_ring *ring, struct pending_req *req)
  * Routines for managing virtual block devices (vbds).
  */
 static int xen_vbd_translate(struct phys_req *req, struct xen_blkif *blkif,
-			     int operation)
+			     enum req_op operation)
 {
 	struct xen_vbd *vbd = &blkif->vbd;
 	int rc = -EACCES;
@@ -1193,8 +1193,8 @@ static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
 	struct bio *bio = NULL;
 	struct bio **biolist = pending_req->biolist;
 	int i, nbio = 0;
-	int operation;
-	int operation_flags = 0;
+	enum req_op operation;
+	blk_opf_t operation_flags = 0;
 	struct blk_plug plug;
 	bool drain = false;
 	struct grant_page **pages = pending_req->segments;