btrfs: add btrfs_trans_handle->fs_info pointer

btrfs_trans_handle->root is documented as for use for confirming
that the root passed in to start the transaction is the same as the
one ending it.  It's used in several places when an fs_info pointer
is needed, so let's just add an fs_info pointer directly.  Eventually,
the root pointer can be removed.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -4589,7 +4589,7 @@ out:
 	 */
 	if (trans->can_flush_pending_bgs &&
 	    trans->chunk_bytes_reserved >= (u64)SZ_2M) {
-		btrfs_create_pending_block_groups(trans, trans->root);
+		btrfs_create_pending_block_groups(trans, extent_root);
 		btrfs_trans_release_chunk_metadata(trans);
 	}
 	return ret;
@@ -5730,7 +5730,7 @@ void btrfs_trans_release_metadata(struct btrfs_trans_handle *trans,
  */
 void btrfs_trans_release_chunk_metadata(struct btrfs_trans_handle *trans)
 {
-	struct btrfs_fs_info *fs_info = trans->root->fs_info;
+	struct btrfs_fs_info *fs_info = trans->fs_info;
 
 	if (!trans->chunk_bytes_reserved)
 		return;
@@ -8543,7 +8543,7 @@ static int record_one_subtree_extent(struct btrfs_trans_handle *trans,
 
 	delayed_refs = &trans->transaction->delayed_refs;
 	spin_lock(&delayed_refs->lock);
-	if (btrfs_qgroup_insert_dirty_extent(trans->root->fs_info,
+	if (btrfs_qgroup_insert_dirty_extent(trans->fs_info,
 					     delayed_refs, qrecord))
 		kfree(qrecord);
 	spin_unlock(&delayed_refs->lock);

fs/btrfs/qgroup.c

@@ -2196,7 +2196,7 @@ void assert_qgroups_uptodate(struct btrfs_trans_handle *trans)
 {
 	if (list_empty(&trans->qgroup_ref_list) && !trans->delayed_ref_elem.seq)
 		return;
-	btrfs_err(trans->root->fs_info,
+	btrfs_err(trans->fs_info,
 		"qgroups not uptodate in trans handle %p:  list is%s empty, "
 		"seq is %#x.%x",
 		trans, list_empty(&trans->qgroup_ref_list) ? "" : " not",

fs/btrfs/transaction.c

@@ -561,6 +561,7 @@ again:
 	h->transaction = cur_trans;
 	h->root = root;
 	h->use_count = 1;
+	h->fs_info = root->fs_info;
 
 	h->type = type;
 	h->can_flush_pending_bgs = true;

fs/btrfs/transaction.h

@@ -128,6 +128,7 @@ struct btrfs_trans_handle {
 	 * Subvolume quota depends on this
 	 */
 	struct btrfs_root *root;
+	struct btrfs_fs_info *fs_info;
 	struct seq_list delayed_ref_elem;
 	struct list_head qgroup_ref_list;
 	struct list_head new_bgs;