mount namespace + d_path question

Hello, Question regarding pathnames and mount namespaces. As I understand mount namespaces enable different processes to mount filesystems at different locations leading to different paths to the same underlying file. When you do something like the below in kernel code: d_path(&file->f_path, filename, PATH_MAX+11); How can you guarantee that the returned full path is against the root/init mount namespace instead of the calling process' mount namespace? Thanks David