btrfs: support cloned bios in btree_csum_one_bio

To allow splitting bios in btrfs_submit_bio, btree_csum_one_bio needs to
be able to handle cloned bios.  As btree_csum_one_bio is always called
before handing the bio to the block layer that is trivially done by using
bio_for_each_segment instead of bio_for_each_segment_all.  Also switch
the function to take a btrfs_bio and use that to derive the fs_info.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/bio.c

@@ -437,7 +437,7 @@ static void __btrfs_submit_bio(struct bio *bio, struct btrfs_io_context *bioc,
 static blk_status_t btrfs_bio_csum(struct btrfs_bio *bbio)
 {
 	if (bbio->bio.bi_opf & REQ_META)
-		return btree_csum_one_bio(&bbio->bio);
+		return btree_csum_one_bio(bbio);
 	return btrfs_csum_one_bio(bbio);
 }
 

fs/btrfs/disk-io.c

@@ -438,17 +438,15 @@ static int csum_dirty_buffer(struct btrfs_fs_info *fs_info, struct bio_vec *bvec
 	return csum_one_extent_buffer(eb);
 }
 
-blk_status_t btree_csum_one_bio(struct bio *bio)
+blk_status_t btree_csum_one_bio(struct btrfs_bio *bbio)
 {
-	struct bio_vec *bvec;
-	struct btrfs_root *root;
-	struct bvec_iter_all iter_all;
+	struct btrfs_fs_info *fs_info = bbio->inode->root->fs_info;
+	struct bvec_iter iter;
+	struct bio_vec bv;
 	int ret = 0;
 
-	ASSERT(!bio_flagged(bio, BIO_CLONED));
-	bio_for_each_segment_all(bvec, bio, iter_all) {
-		root = BTRFS_I(bvec->bv_page->mapping->host)->root;
-		ret = csum_dirty_buffer(root->fs_info, bvec);
+	bio_for_each_segment(bv, &bbio->bio, iter) {
+		ret = csum_dirty_buffer(fs_info, &bv);
 		if (ret)
 			break;
 	}

fs/btrfs/disk-io.h

@@ -114,7 +114,7 @@ int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid,
 int btrfs_read_extent_buffer(struct extent_buffer *buf,
 			     struct btrfs_tree_parent_check *check);
 
-blk_status_t btree_csum_one_bio(struct bio *bio);
+blk_status_t btree_csum_one_bio(struct btrfs_bio *bbio);
 int btrfs_alloc_log_tree_node(struct btrfs_trans_handle *trans,
 			      struct btrfs_root *root);
 int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,