btrfs: introduce submit_compressed_bio() for compression

The new helper, submit_compressed_bio(), will aggregate the following
work:

- Increase compressed_bio::pending_bios
- Remap the endio function
- Map and submit the bio

This slightly reorders calls to btrfs_csum_one_bio or
btrfs_lookup_bio_sums but but none of them does anything regarding IO
submission so this is effectively no change. We mainly care about order
of

- atomic_inc
- btrfs_bio_wq_end_io
- btrfs_map_bio
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -419,6 +419,21 @@ static void end_compressed_bio_write(struct bio *bio)
 	bio_put(bio);
 }
 
+static blk_status_t submit_compressed_bio(struct btrfs_fs_info *fs_info,
+					  struct compressed_bio *cb,
+					  struct bio *bio, int mirror_num)
+{
+	blk_status_t ret;
+
+	ASSERT(bio->bi_iter.bi_size);
+	atomic_inc(&cb->pending_bios);
+	ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
+	if (ret)
+		return ret;
+	ret = btrfs_map_bio(fs_info, bio, mirror_num);
+	return ret;
+}
+
 /*
  * worker function to build and submit bios for previously compressed pages.
  * The corresponding pages in the inode should be marked for writeback
@@ -514,19 +529,13 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 
 		page->mapping = NULL;
 		if (submit || len < PAGE_SIZE) {
-			atomic_inc(&cb->pending_bios);
-			ret = btrfs_bio_wq_end_io(fs_info, bio,
-						  BTRFS_WQ_ENDIO_DATA);
-			if (ret)
-				goto finish_cb;
-
 			if (!skip_sum) {
 				ret = btrfs_csum_one_bio(inode, bio, start, 1);
 				if (ret)
 					goto finish_cb;
 			}
 
-			ret = btrfs_map_bio(fs_info, bio, 0);
+			ret = submit_compressed_bio(fs_info, cb, bio, 0);
 			if (ret)
 				goto finish_cb;
 
@@ -553,18 +562,13 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 		cond_resched();
 	}
 
-	atomic_inc(&cb->pending_bios);
-	ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
-	if (ret)
-		goto last_bio;
-
 	if (!skip_sum) {
 		ret = btrfs_csum_one_bio(inode, bio, start, 1);
 		if (ret)
 			goto last_bio;
 	}
 
-	ret = btrfs_map_bio(fs_info, bio, 0);
+	ret = submit_compressed_bio(fs_info, cb, bio, 0);
 	if (ret)
 		goto last_bio;
 
@@ -868,12 +872,6 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		if (submit || bio_add_page(comp_bio, page, pg_len, 0) < pg_len) {
 			unsigned int nr_sectors;
 
-			atomic_inc(&cb->pending_bios);
-			ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
-						  BTRFS_WQ_ENDIO_DATA);
-			if (ret)
-				goto finish_cb;
-
 			ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
 			if (ret)
 				goto finish_cb;
@@ -882,7 +880,7 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 						  fs_info->sectorsize);
 			sums += fs_info->csum_size * nr_sectors;
 
-			ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
+			ret = submit_compressed_bio(fs_info, cb, comp_bio, mirror_num);
 			if (ret)
 				goto finish_cb;
 
@@ -897,16 +895,11 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		cur_disk_byte += pg_len;
 	}
 
-	atomic_inc(&cb->pending_bios);
-	ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
-	if (ret)
-		goto last_bio;
-
 	ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
 	if (ret)
 		goto last_bio;
 
-	ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
+	ret = submit_compressed_bio(fs_info, cb, comp_bio, mirror_num);
 	if (ret)
 		goto last_bio;