block: add a rq_integrity_vec helper

This provides a nice little shortcut to get the integrity data for
drivers like NVMe that only support a single integrity segment.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>

include/linux/blkdev.h

@@ -1559,6 +1559,17 @@ static inline unsigned int bio_integrity_bytes(struct blk_integrity *bi,
 	return bio_integrity_intervals(bi, sectors) * bi->tuple_size;
 }
 
+/*
+ * Return the first bvec that contains integrity data.  Only drivers that are
+ * limited to a single integrity segment should use this helper.
+ */
+static inline struct bio_vec *rq_integrity_vec(struct request *rq)
+{
+	if (WARN_ON_ONCE(queue_max_integrity_segments(rq->q) > 1))
+		return NULL;
+	return rq->bio->bi_integrity->bip_vec;
+}
+
 #else /* CONFIG_BLK_DEV_INTEGRITY */
 
 struct bio;
@@ -1633,6 +1644,11 @@ static inline unsigned int bio_integrity_bytes(struct blk_integrity *bi,
 	return 0;
 }
 
+static inline struct bio_vec *rq_integrity_vec(struct request *rq)
+{
+	return NULL;
+}
+
 #endif /* CONFIG_BLK_DEV_INTEGRITY */
 
 struct block_device_operations {