The 'translate' function is a great place to put this in IMO as it is possible to get both untranslated and translated cmdbufs. However a kernel reference has to be passed here, but it is not too hard fortunately.
Right now only MappedBuffers that only span a single page and are not aligned are implemented.
MappedBuffers are unmapped during the reply part of ReplyAndReceive. Only unmapping of ReadOnly buffers is currently implemented.