  Seifert derived an exact fluctuation relation for diffusion processes using
the concept of "stochastic system entropy". In this note we extend his
formalism to entropic transport. We introduce the notion of relative stochastic
entropy, or "relative surprisal", and use it to generalize Seifert's
system/medium decomposition of the total entropy. This result allows to apply
the concepts of stochastic thermodynamics to diffusion processes in confined
geometries, such as ion channels, cellular pores or nanoporous materials. It
can be seen as the equivalent for diffusion processes of Esposito and
Schaller's generalized fluctuation theorem for "Maxwell demon feedbacks".
