block: make part_in_flight() take an array of two ints

Instead of returning the count that matches the partition, pass
in an array of two ints. Index 0 will be filled with the inflight
count for the partition in question, and index 1 will filled
with the root inflight count, if the partition passed in is not the
root.

This is in preparation for being able to calculate both in one
go.
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -1472,15 +1472,15 @@ static void add_acct_request(struct request_queue *q, struct request *rq,
 static void part_round_stats_single(struct request_queue *q, int cpu,
 				    struct hd_struct *part, unsigned long now)
 {
-	int inflight;
+	int inflight[2];
 
 	if (now == part->stamp)
 		return;
 
-	inflight = part_in_flight(q, part);
-	if (inflight) {
+	part_in_flight(q, part, inflight);
+	if (inflight[0]) {
 		__part_stat_add(cpu, part, time_in_queue,
-				inflight * (now - part->stamp));
+				inflight[0] * (now - part->stamp));
 		__part_stat_add(cpu, part, io_ticks, (now - part->stamp));
 	}
 	part->stamp = now;

block/genhd.c

@@ -1204,6 +1204,7 @@ static int diskstats_show(struct seq_file *seqf, void *v)
 	struct disk_part_iter piter;
 	struct hd_struct *hd;
 	char buf[BDEVNAME_SIZE];
+	unsigned int inflight[2];
 	int cpu;
 
 	/*
@@ -1219,6 +1220,7 @@ static int diskstats_show(struct seq_file *seqf, void *v)
 		cpu = part_stat_lock();
 		part_round_stats(gp->queue, cpu, hd);
 		part_stat_unlock();
+		part_in_flight(gp->queue, hd, inflight);
 		seq_printf(seqf, "%4d %7d %s %lu %lu %lu "
 			   "%u %lu %lu %lu %u %u %u %u\n",
 			   MAJOR(part_devt(hd)), MINOR(part_devt(hd)),
@@ -1231,7 +1233,7 @@ static int diskstats_show(struct seq_file *seqf, void *v)
 			   part_stat_read(hd, merges[WRITE]),
 			   part_stat_read(hd, sectors[WRITE]),
 			   jiffies_to_msecs(part_stat_read(hd, ticks[WRITE])),
-			   part_in_flight(gp->queue, hd),
+			   inflight[0],
 			   jiffies_to_msecs(part_stat_read(hd, io_ticks)),
 			   jiffies_to_msecs(part_stat_read(hd, time_in_queue))
 			);

block/partition-generic.c

@@ -113,11 +113,13 @@ ssize_t part_stat_show(struct device *dev,
 {
 	struct hd_struct *p = dev_to_part(dev);
 	struct request_queue *q = dev_to_disk(dev)->queue;
+	unsigned int inflight[2];
 	int cpu;
 
 	cpu = part_stat_lock();
 	part_round_stats(q, cpu, p);
 	part_stat_unlock();
+	part_in_flight(q, p, inflight);
 	return sprintf(buf,
 		"%8lu %8lu %8llu %8u "
 		"%8lu %8lu %8llu %8u "
@@ -131,7 +133,7 @@ ssize_t part_stat_show(struct device *dev,
 		part_stat_read(p, merges[WRITE]),
 		(unsigned long long)part_stat_read(p, sectors[WRITE]),
 		jiffies_to_msecs(part_stat_read(p, ticks[WRITE])),
-		part_in_flight(q, p),
+		inflight[0],
 		jiffies_to_msecs(part_stat_read(p, io_ticks)),
 		jiffies_to_msecs(part_stat_read(p, time_in_queue)));
 }

include/linux/genhd.h

@@ -378,11 +378,18 @@ static inline void part_dec_in_flight(struct request_queue *q,
 		atomic_dec(&part_to_disk(part)->part0.in_flight[rw]);
 }
 
-static inline int part_in_flight(struct request_queue *q,
-				 struct hd_struct *part)
+static inline void part_in_flight(struct request_queue *q,
+				  struct hd_struct *part,
+				  unsigned int inflight[2])
 {
-	return atomic_read(&part->in_flight[0]) +
+	inflight[0] = atomic_read(&part->in_flight[0]) +
 			atomic_read(&part->in_flight[1]);
+	if (part->partno) {
+		part = &part_to_disk(part)->part0;
+		inflight[1] = atomic_read(&part->in_flight[0]) +
+				atomic_read(&part->in_flight[1]);
+	} else
+		inflight[1] = 0;
 }
 
 static inline struct partition_meta_info *alloc_part_info(struct gendisk *disk)