block: export passthrough stats enabled

A user can enable io accounting for passthrough requests, so export the
helper that checks if the request should be tracked. This will enable
stacking drivers to to report iostats for passthrough workloads. Since
the stacking request_queue may not be the one providing the request, the
API has to add a parameter for the caller to specify which one to check.

Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Nitesh Shetty <nj.shetty@samsung.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260528010041.1533124-2-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 40 insertions, 0 deletions

diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 24b4160aeaad..af878597afb8 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -1252,4 +1252,44 @@ static inline int blk_rq_map_sg(struct request *rq, struct scatterlist *sglist)
 }
 void blk_dump_rq_flags(struct request *, char *);
 
+/**
+ * blk_rq_passthrough_stats - check if this request should account stats
+ * @rq: request to check
+ * @q: the queue accumulating the stats
+ *
+ * Note, @q does not necessarily need to be the request_queue that provides
+ * @rq.
+ *
+ * Return: true if stats should be accounted.
+ */
+static inline bool blk_rq_passthrough_stats(struct request *rq,
+					    struct request_queue *q)
+{
+	struct bio *bio = rq->bio;
+
+	if (!blk_queue_passthrough_stat(q))
+		return false;
+
+	/* Requests without a bio do not transfer data. */
+	if (!bio)
+		return false;
+
+	/*
+	 * Stats are accumulated in the bdev, so must have one attached to a
+	 * bio to track stats. Most drivers do not set the bdev for passthrough
+	 * requests, but nvme is one that will set it.
+	 */
+	if (!bio->bi_bdev)
+		return false;
+
+	/*
+	 * We don't know what a passthrough command does, but we know the
+	 * payload size and data direction. Ensuring the size is aligned to the
+	 * block size filters out most commands with payloads that don't
+	 * represent sector access.
+	 */
+	if (blk_rq_bytes(rq) & (bdev_logical_block_size(bio->bi_bdev) - 1))
+		return false;
+	return true;
+}
 #endif /* BLK_MQ_H */