[PATCH 2/2] btrfs: use bio::remaining for async checksumming synchronization

[Daniel Vacek <neelx@suse.com>]

We can use bio::remaining counter to sync the offloaded checksuming.
As a result we can slim down the btrfs_bio structure by 24 bytes
and simplify the code a bit.

$ pahole | diff
-	/* size: 328, cachelines: 6, members: 15 */
+	/* size: 304, cachelines: 5, members: 14 */

Moreover this will allow us enabling async checksumming with encryption
where we need to checksum the bounce bio instead of our regular one
embedded in btrfs_bio. And so we need to extend it's lifetime. This is
the preffered way to do so.

Signed-off-by: Daniel Vacek <neelx@suse.com>
---
 fs/btrfs/bio.c       | 4 ----
 fs/btrfs/bio.h       | 4 ----
 fs/btrfs/file-item.c | 6 ++----
 3 files changed, 2 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/bio.c b/fs/btrfs/bio.c
index 19b4855969f5..771b7d598aee 100644
--- a/fs/btrfs/bio.c
+++ b/fs/btrfs/bio.c
@@ -103,7 +103,6 @@ static struct btrfs_bio *btrfs_split_bio(struct btrfs_fs_info *fs_info,
 	bbio->can_use_append = orig_bbio->can_use_append;
 	bbio->is_scrub = orig_bbio->is_scrub;
 	bbio->is_remap = orig_bbio->is_remap;
-	bbio->async_csum = orig_bbio->async_csum;
 
 	atomic_inc(&orig_bbio->pending_ios);
 	return bbio;
@@ -114,9 +113,6 @@ void btrfs_bio_end_io(struct btrfs_bio *bbio, blk_status_t status)
 	/* Make sure we're already in task context. */
 	ASSERT(in_task());
 
-	if (bbio->async_csum)
-		wait_for_completion(&bbio->csum_done);
-
 	bbio->bio.bi_status = status;
 	if (bbio->bio.bi_pool == &btrfs_clone_bioset) {
 		struct btrfs_bio *orig_bbio = bbio->private;
diff --git a/fs/btrfs/bio.h b/fs/btrfs/bio.h
index b7bd377a0162..bbf362b8668b 100644
--- a/fs/btrfs/bio.h
+++ b/fs/btrfs/bio.h
@@ -58,7 +58,6 @@ struct btrfs_bio {
 			struct btrfs_ordered_extent *ordered;
 			struct btrfs_ordered_sum *sums;
 			struct work_struct csum_work;
-			struct completion csum_done;
 			struct bvec_iter csum_saved_iter;
 			u64 orig_physical;
 			u64 orig_logical;
@@ -93,9 +92,6 @@ struct btrfs_bio {
 	/* Whether the bio is coming from copy_remapped_data_io(). */
 	bool is_remap:1;
 
-	/* Whether the csum generation for data write is async. */
-	bool async_csum:1;
-
 	/* Whether the bio is written using zone append. */
 	bool can_use_append:1;
 
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 5a5cffb18922..50dcd448d936 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -817,9 +817,8 @@ static void csum_one_bio_work(struct work_struct *work)
 	struct btrfs_bio *bbio = container_of(work, struct btrfs_bio, csum_work);
 
 	ASSERT(btrfs_op(&bbio->bio) == BTRFS_MAP_WRITE);
-	ASSERT(bbio->async_csum == true);
 	csum_one_bio(bbio, &bbio->csum_saved_iter);
-	complete(&bbio->csum_done);
+	bio_endio(&bbio->bio);
 }
 
 /*
@@ -854,8 +853,7 @@ int btrfs_csum_one_bio(struct btrfs_bio *bbio, bool async)
 		csum_one_bio(bbio, &iter);
 		return 0;
 	}
-	init_completion(&bbio->csum_done);
-	bbio->async_csum = true;
+	bio_inc_remaining(bio);
 	bbio->csum_saved_iter = bio->bi_iter;
 	INIT_WORK(&bbio->csum_work, csum_one_bio_work);
 	schedule_work(&bbio->csum_work);
-- 
2.53.0