[PATCH for-next v3 4/5] null_blk: pass transfer size to null_handle_rq()

["Shin'ichiro Kawasaki" <shinichiro.kawasaki@xxxxxxx>]

As preparation to support partial data transfer, add a new argument to
null_handle_rq() to pass the number of sectors to transfer. This commit
does not change the behavior.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
---
 drivers/block/null_blk/main.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 87037cb375c9..71c86775354e 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -1263,25 +1263,36 @@ static int null_transfer(struct nullb *nullb, struct page *page,
 	return err;
 }
 
-static blk_status_t null_handle_rq(struct nullb_cmd *cmd)
+/*
+ * Transfer data for the given request. The transfer size is capped with the
+ * nr_sectors argument.
+ */
+static blk_status_t null_handle_rq(struct nullb_cmd *cmd, sector_t nr_sectors)
 {
 	struct request *rq = blk_mq_rq_from_pdu(cmd);
 	struct nullb *nullb = cmd->nq->dev->nullb;
 	int err = 0;
 	unsigned int len;
 	sector_t sector = blk_rq_pos(rq);
+	unsigned int max_bytes = nr_sectors << SECTOR_SHIFT;
+	unsigned int transferred_bytes = 0;
 	struct req_iterator iter;
 	struct bio_vec bvec;
 
 	spin_lock_irq(&nullb->lock);
 	rq_for_each_segment(bvec, rq, iter) {
 		len = bvec.bv_len;
+		if (transferred_bytes + len > max_bytes)
+			len = max_bytes - transferred_bytes;
 		err = null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset,
 				     op_is_write(req_op(rq)), sector,
 				     rq->cmd_flags & REQ_FUA);
 		if (err)
 			break;
 		sector += len >> SECTOR_SHIFT;
+		transferred_bytes += len;
+		if (transferred_bytes >= max_bytes)
+			break;
 	}
 	spin_unlock_irq(&nullb->lock);
 
@@ -1333,7 +1344,7 @@ blk_status_t null_handle_memory_backed(struct nullb_cmd *cmd, enum req_op op,
 	if (op == REQ_OP_DISCARD)
 		return null_handle_discard(dev, sector, nr_sectors);
 
-	return null_handle_rq(cmd);
+	return null_handle_rq(cmd, nr_sectors);
 }
 
 static void nullb_zero_read_cmd_buffer(struct nullb_cmd *cmd)
-- 
2.47.0