block: move stats from disk to part0

Move stats related fields - stamp, in_flight, dkstats - from disk to
part0 and unify stat handling such that...

* part_stat_*() now updates part0 together if the specified partition
  is not part0.  ie. part_stat_*() are now essentially all_stat_*().

* {disk|all}_stat_*() are gone.

* part_round_stats() is updated similary.  It handles part0 stats
  automatically and disk_round_stats() is killed.

* part_{inc|dec}_in_fligh() is implemented which automatically updates
  part0 stats for parts other than part0.

* disk_map_sector_rcu() is updated to return part0 if no part matches.
  Combined with the above changes, this makes NULL special case
  handling in callers unnecessary.

* Separate stats show code paths for disk are collapsed into part
  stats show code paths.

* Rename disk_stat_lock/unlock() to part_stat_lock/unlock()

While at it, reposition stat handling macros a bit and add missing
parentheses around macro parameters.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 4 insertions, 8 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index d926a24..c77196d 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -390,17 +390,13 @@ static int attempt_merge(struct request_queue *q, struct request *req,
 		struct hd_struct *part;
 		int cpu;
 
-		cpu = disk_stat_lock();
+		cpu = part_stat_lock();
 		part = disk_map_sector_rcu(req->rq_disk, req->sector);
 
-		disk_round_stats(cpu, req->rq_disk);
-		req->rq_disk->in_flight--;
-		if (part) {
-			part_round_stats(cpu, part);
-			part->in_flight--;
-		}
+		part_round_stats(cpu, part);
+		part_dec_in_flight(part);
 
-		disk_stat_unlock();
+		part_stat_unlock();
 	}
 
 	req->ioprio = ioprio_best(req->ioprio, next->ioprio);