[PATCH 2/5] block: add request->io_data_len

[Tejun Heo]

Currently, at the time of completeion, there's no way of knowing how big a
request was. blk-iocost will need this information to account for IO size when
calculating expected latencies.

This patch adds rq->io_data_len which remembers blk_rq_bytes() at the time the
request gets issued. The field is enabled iff CONFIG_BLK_IO_DATA_LEN is set and
doesn't increase the size of the struct even when enabled.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 block/Kconfig          | 3 +++
 block/blk-mq.c         | 6 ++++++
 include/linux/blkdev.h | 8 ++++++++
 3 files changed, 17 insertions(+)

diff --git a/block/Kconfig b/block/Kconfig
index 3bc76bb113a0..48308e600dc8 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -26,6 +26,9 @@ menuconfig BLOCK
 
 if BLOCK
 
+config BLK_RQ_IO_DATA_LEN
+	bool
+
 config BLK_RQ_ALLOC_TIME
 	bool
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index f6291ceedee4..64ed22712fe4 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -415,6 +415,9 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
 		return ERR_PTR(-EWOULDBLOCK);
 
 	rq->__data_len = 0;
+#ifdef CONFIG_BLK_RQ_IO_DATA_LEN
+	rq->io_data_len = 0;
+#endif
 	rq->__sector = (sector_t) -1;
 	rq->bio = rq->biotail = NULL;
 	return rq;
@@ -655,6 +658,9 @@ void blk_mq_start_request(struct request *rq)
 
 	trace_block_rq_issue(q, rq);
 
+#ifdef CONFIG_BLK_RQ_IO_DATA_LEN
+	rq->io_data_len = blk_rq_bytes(rq);
+#endif
 	if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) {
 		rq->io_start_time_ns = ktime_get_ns();
 		rq->stats_sectors = blk_rq_sectors(rq);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 32868fbedc9e..bfd34c6a27ef 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -142,6 +142,14 @@ struct request {
 
 	/* the following two fields are internal, NEVER access directly */
 	unsigned int __data_len;	/* total data len */
+#ifdef CONFIG_BLK_RQ_IO_DATA_LEN
+	/*
+	 * Total data len at the time of issue. This doesn't get deducted by
+	 * blk_update_request() and can be used by completion path to determine
+	 * the request size.
+	 */
+	unsigned int io_data_len;
+#endif
 	sector_t __sector;		/* sector cursor */
 
 	struct bio *bio;
-- 
2.25.1