block/xen-blkfront: Split blkif_queue_request in 2

Currently, blkif_queue_request has 2 distinct execution path:
    - Send a discard request
    - Send a read/write request

The function is also allocating grants to use for generating the
request. Although, this is only used for read/write request.

Rather than having a function with 2 distinct execution path, separate
the function in 2. This will also remove one level of tabulation.
Signed-off-by: NJulien Grall <julien.grall@citrix.com>
Reviewed-by: NRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: NDavid Vrabel <david.vrabel@citrix.com>

drivers/block/xen-blkfront.c

@@ -394,13 +394,35 @@ static int blkif_ioctl(struct block_device *bdev, fmode_t mode,
 	return 0;
 }
 
-/*
- * Generate a Xen blkfront IO request from a blk layer request.  Reads
- * and writes are handled as expected.
- *
- * @req: a request struct
- */
-static int blkif_queue_request(struct request *req)
+static int blkif_queue_discard_req(struct request *req)
+{
+	struct blkfront_info *info = req->rq_disk->private_data;
+	struct blkif_request *ring_req;
+	unsigned long id;
+
+	/* Fill out a communications ring structure. */
+	ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
+	id = get_id_from_freelist(info);
+	info->shadow[id].request = req;
+
+	ring_req->operation = BLKIF_OP_DISCARD;
+	ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
+	ring_req->u.discard.id = id;
+	ring_req->u.discard.sector_number = (blkif_sector_t)blk_rq_pos(req);
+	if ((req->cmd_flags & REQ_SECURE) && info->feature_secdiscard)
+		ring_req->u.discard.flag = BLKIF_DISCARD_SECURE;
+	else
+		ring_req->u.discard.flag = 0;
+
+	info->ring.req_prod_pvt++;
+
+	/* Keep a private copy so we can reissue requests when recovering. */
+	info->shadow[id].req = *ring_req;
+
+	return 0;
+}
+
+static int blkif_queue_rw_req(struct request *req)
 {
 	struct blkfront_info *info = req->rq_disk->private_data;
 	struct blkif_request *ring_req;
@@ -420,9 +442,6 @@ static int blkif_queue_request(struct request *req)
 	struct scatterlist *sg;
 	int nseg, max_grefs;
 
-	if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
-		return 1;
-
 	max_grefs = req->nr_phys_segments;
 	if (max_grefs > BLKIF_MAX_SEGMENTS_PER_REQUEST)
 		/*
@@ -452,16 +471,6 @@ static int blkif_queue_request(struct request *req)
 	id = get_id_from_freelist(info);
 	info->shadow[id].request = req;
 
-	if (unlikely(req->cmd_flags & (REQ_DISCARD | REQ_SECURE))) {
-		ring_req->operation = BLKIF_OP_DISCARD;
-		ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
-		ring_req->u.discard.id = id;
-		ring_req->u.discard.sector_number = (blkif_sector_t)blk_rq_pos(req);
-		if ((req->cmd_flags & REQ_SECURE) && info->feature_secdiscard)
-			ring_req->u.discard.flag = BLKIF_DISCARD_SECURE;
-		else
-			ring_req->u.discard.flag = 0;
-	} else {
 	BUG_ON(info->max_indirect_segments == 0 &&
 	       req->nr_phys_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
 	BUG_ON(info->max_indirect_segments &&
@@ -487,11 +496,11 @@ static int blkif_queue_request(struct request *req)
 			BLKIF_OP_WRITE : BLKIF_OP_READ;
 		if (req->cmd_flags & (REQ_FLUSH | REQ_FUA)) {
 			/*
-				 * Ideally we can do an unordered flush-to-disk. In case the
-				 * backend onlysupports barriers, use that. A barrier request
-				 * a superset of FUA, so we can implement it the same
-				 * way.  (It's also a FLUSH+FUA, since it is
-				 * guaranteed ordered WRT previous writes.)
+			 * Ideally we can do an unordered flush-to-disk.
+			 * In case the backend onlysupports barriers, use that.
+			 * A barrier request a superset of FUA, so we can
+			 * implement it the same way.  (It's also a FLUSH+FUA,
+			 * since it is guaranteed ordered WRT previous writes.)
 			 */
 			switch (info->feature_flush &
 				((REQ_FLUSH|REQ_FUA))) {
@@ -524,7 +533,10 @@ static int blkif_queue_request(struct request *req)
 			if (!info->feature_persistent) {
 				struct page *indirect_page;
 
-					/* Fetch a pre-allocated page to use for indirect grefs */
+				/*
+				 * Fetch a pre-allocated page to use for
+				 * indirect grefs
+				 */
 				BUG_ON(list_empty(&info->indirect_pages));
 				indirect_page = list_first_entry(&info->indirect_pages,
 								 struct page, lru);
@@ -584,7 +596,6 @@ static int blkif_queue_request(struct request *req)
 	}
 	if (segments)
 		kunmap_atomic(segments);
-	}
 
 	info->ring.req_prod_pvt++;
 
@@ -597,6 +608,24 @@ static int blkif_queue_request(struct request *req)
 	return 0;
 }
 
+/*
+ * Generate a Xen blkfront IO request from a blk layer request.  Reads
+ * and writes are handled as expected.
+ *
+ * @req: a request struct
+ */
+static int blkif_queue_request(struct request *req)
+{
+	struct blkfront_info *info = req->rq_disk->private_data;
+
+	if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
+		return 1;
+
+	if (unlikely(req->cmd_flags & (REQ_DISCARD | REQ_SECURE)))
+		return blkif_queue_discard_req(req);
+	else
+		return blkif_queue_rw_req(req);
+}
 
 static inline void flush_requests(struct blkfront_info *info)
 {