Btrfs: add qgroup inheritance

When creating a subvolume or snapshot, it is necessary
to initialize the qgroup account with a copy of some
other (tracking) qgroup. This patch adds parameters
to the ioctls to pass the information from which qgroup
to inherit.

Signed-off-by: Arne Jansen <sensille@gmx.net>
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 2759e057..cca315d 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -73,6 +73,7 @@
 	struct dentry *dentry;
 	struct btrfs_root *root;
 	struct btrfs_root *snap;
+	struct btrfs_qgroup_inherit *inherit;
 	/* block reservation for the operation */
 	struct btrfs_block_rsv block_rsv;
 	/* extra metadata reseration for relocation */