block: export API to get the number of bdev inflight IO

- rename part_in_{flight, flight_rw} to bdev_count_{inflight, inflight_rw}
- export bdev_count_inflight, to fix a problem in mdraid that foreground
  IO can be starved by background sync IO in later patches

Link: https://lore.kernel.org/linux-raid/20250506124903.2540268-6-yukuai1@huaweicloud.com
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>

4 files changed, 19 insertions, 8 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index e8cc270a453f..b862c66018f2 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1018,7 +1018,7 @@ again:
 	stamp = READ_ONCE(part->bd_stamp);
 	if (unlikely(time_after(now, stamp)) &&
 	    likely(try_cmpxchg(&part->bd_stamp, &stamp, now)) &&
-	    (end || part_in_flight(part)))
+	    (end || bdev_count_inflight(part)))
 		__part_stat_add(part, io_ticks, now - stamp);
 
 	if (bdev_is_partition(part)) {
diff --git a/block/blk.h b/block/blk.h
index 665b3d1fb504..21af4f0c4c00 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -419,7 +419,6 @@ void blk_apply_bdi_limits(struct backing_dev_info *bdi,
 int blk_dev_init(void);
 
 void update_io_ticks(struct block_device *part, unsigned long now, bool end);
-unsigned int part_in_flight(struct block_device *part);
 
 static inline void req_set_nomerge(struct request_queue *q, struct request *req)
 {
diff --git a/block/genhd.c b/block/genhd.c
index 1c1a642b321e..8171a6bc3210 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -125,7 +125,7 @@ static void part_stat_read_all(struct block_device *part,
 	}
 }
 
-static void part_in_flight_rw(struct block_device *part,
+static void bdev_count_inflight_rw(struct block_device *part,
 		unsigned int inflight[2], bool mq_driver)
 {
 	int cpu;
@@ -147,14 +147,24 @@ static void part_in_flight_rw(struct block_device *part,
 		inflight[WRITE] = 0;
 }
 
-unsigned int part_in_flight(struct block_device *part)
+/**
+ * bdev_count_inflight - get the number of inflight IOs for a block device.
+ *
+ * @part: the block device.
+ *
+ * Inflight here means started IO accounting, from bdev_start_io_acct() for
+ * bio-based block device, and from blk_account_io_start() for rq-based block
+ * device.
+ */
+unsigned int bdev_count_inflight(struct block_device *part)
 {
 	unsigned int inflight[2] = {0};
 
-	part_in_flight_rw(part, inflight, false);
+	bdev_count_inflight_rw(part, inflight, false);
 
 	return inflight[READ] + inflight[WRITE];
 }
+EXPORT_SYMBOL_GPL(bdev_count_inflight);
 
 /*
  * Can be deleted altogether. Later.
@@ -1052,7 +1062,7 @@ ssize_t part_stat_show(struct device *dev,
 	struct disk_stats stat;
 	unsigned int inflight;
 
-	inflight = part_in_flight(bdev);
+	inflight = bdev_count_inflight(bdev);
 	if (inflight) {
 		part_stat_lock();
 		update_io_ticks(bdev, jiffies, true);
@@ -1101,7 +1111,7 @@ ssize_t part_inflight_show(struct device *dev, struct device_attribute *attr,
 	struct request_queue *q = bdev_get_queue(bdev);
 	unsigned int inflight[2] = {0};
 
-	part_in_flight_rw(bdev, inflight, queue_is_mq(q));
+	bdev_count_inflight_rw(bdev, inflight, queue_is_mq(q));
 
 	return sysfs_emit(buf, "%8u %8u\n", inflight[READ], inflight[WRITE]);
 }
@@ -1356,7 +1366,7 @@ static int diskstats_show(struct seq_file *seqf, void *v)
 		if (bdev_is_partition(hd) && !bdev_nr_sectors(hd))
 			continue;
 
-		inflight = part_in_flight(hd);
+		inflight = bdev_count_inflight(hd);
 		if (inflight) {
 			part_stat_lock();
 			update_io_ticks(hd, jiffies, true);
diff --git a/include/linux/part_stat.h b/include/linux/part_stat.h
index c5e9cac0575e..eeeff2a04529 100644
--- a/include/linux/part_stat.h
+++ b/include/linux/part_stat.h
@@ -79,4 +79,6 @@ static inline void part_stat_set_all(struct block_device *part, int value)
 #define part_stat_local_read_cpu(part, field, cpu)			\
 	local_read(&(part_stat_get_cpu(part, field, cpu)))
 
+unsigned int bdev_count_inflight(struct block_device *part);
+
 #endif /* _LINUX_PART_STAT_H */