Because code paths for I/O requests are quite complex, add comments above the functions which participate in I/O paths.
Because code paths for I/O requests are quite complex, add comments above
the functions which participate in I/O paths.

MFC after:	1 day

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase