[PATCH 1/3] block: add __bio_start_io_acct() to control start_time

[Mike Snitzer <snitzer@xxxxxxxxxx>]

__bio_start_io_acct() interface is like bio_start_io_acct() that
allows start_time to be passed in. This gives drivers the ability to
defer starting accounting until after IO is issued (but possibily not
entirely due to bio splitting).

Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
 block/blk-core.c       | 27 ++++++++++++++++++++-------
 include/linux/blkdev.h |  1 +
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 97f8bc8d3a79..18cd12fee67d 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1060,21 +1060,30 @@ void update_io_ticks(struct block_device *part, unsigned long now, bool end)
 	}
 }
 
-static unsigned long __part_start_io_acct(struct block_device *part,
-					  unsigned int sectors, unsigned int op)
+static void __part_start_io_acct(struct block_device *part, unsigned int sectors,
+				 unsigned int op, unsigned long start_time)
 {
 	const int sgrp = op_stat_group(op);
-	unsigned long now = READ_ONCE(jiffies);
 
 	part_stat_lock();
-	update_io_ticks(part, now, false);
+	update_io_ticks(part, start_time, false);
 	part_stat_inc(part, ios[sgrp]);
 	part_stat_add(part, sectors[sgrp], sectors);
 	part_stat_local_inc(part, in_flight[op_is_write(op)]);
 	part_stat_unlock();
+}
 
-	return now;
+/**
+ * __bio_start_io_acct - start I/O accounting for bio based drivers
+ * @bio:	bio to start account for
+ * @start_time:	start time that should be passed back to bio_end_io_acct().
+ */
+void __bio_start_io_acct(struct bio *bio, unsigned long start_time)
+{
+	__part_start_io_acct(bio->bi_bdev, bio_sectors(bio),
+			     bio_op(bio), start_time);
 }
+EXPORT_SYMBOL_GPL(__bio_start_io_acct);
 
 /**
  * bio_start_io_acct - start I/O accounting for bio based drivers
@@ -1084,14 +1093,18 @@ static unsigned long __part_start_io_acct(struct block_device *part,
  */
 unsigned long bio_start_io_acct(struct bio *bio)
 {
-	return __part_start_io_acct(bio->bi_bdev, bio_sectors(bio), bio_op(bio));
+	unsigned long now = READ_ONCE(jiffies);
+	__bio_start_io_acct(bio, now);
+	return now;
 }
 EXPORT_SYMBOL_GPL(bio_start_io_acct);
 
 unsigned long disk_start_io_acct(struct gendisk *disk, unsigned int sectors,
 				 unsigned int op)
 {
-	return __part_start_io_acct(disk->part0, sectors, op);
+	unsigned long now = READ_ONCE(jiffies);
+	__part_start_io_acct(disk->part0, sectors, op, now);
+	return now;
 }
 EXPORT_SYMBOL(disk_start_io_acct);
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 9c95df26fc26..ed3cd5f7f984 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1258,6 +1258,7 @@ unsigned long disk_start_io_acct(struct gendisk *disk, unsigned int sectors,
 void disk_end_io_acct(struct gendisk *disk, unsigned int op,
 		unsigned long start_time);
 
+void __bio_start_io_acct(struct bio *bio, unsigned long start_time);
 unsigned long bio_start_io_acct(struct bio *bio);
 void bio_end_io_acct_remapped(struct bio *bio, unsigned long start_time,
 		struct block_device *orig_bdev);
-- 
2.15.0