Rename function according to actual query.

* While the previous name suggested a fileID, a streamID is used instead
  and the map is by now also used for collectively opened streams.
* Also adjust documentation to mirror actual behaviour.

src/pio_server.c

@@ -664,9 +664,9 @@ writeNetCDFStreamParallel(size_t streamIdx, struct streamMapping *mapping, void
 #endif
 #if defined(HAVE_LIBNETCDF)
 /* needed for writing when some files are only written to by a single process */
-/* cdiOpenFileMap(fileID) gives the writer process */
+/* cdiOpenStreamMap(streamID) gives the writer process */
 static int
-cdiPioSerialOpenFileMap(int streamID)
+cdiPioStream2Owner(int streamID)
 {
   size_t streamIdx = indexOfID(&openStreams, streamID);
   xassert(streamIdx < SIZE_MAX);
@@ -710,7 +710,7 @@ cdiPioCloseFileOnRank(int rank)
 static void
 cdiPioServerCdfDefVars(stream_t *streamptr)
 {
-  int rank, rankOpen = cdiPioSerialOpenFileMap(streamptr->self);
+  int rank, rankOpen = cdiPioStream2Owner(streamptr->self);
   if (commInqIOMode() == PIO_NONE
 #ifdef HAVE_PARALLEL_NC4
       || rankOpen == CDI_PIO_COLLECTIVE_OPEN
@@ -729,7 +729,7 @@ writeNetCDFStreamSerial(size_t streamIdx, struct streamMapping *mapping, void **
    * which has data for which variable (var owner)
    * three cases need to be distinguished */
   const int streamID = openStreams.entries[streamIdx], vlistID = streamInqVlist(streamID);
-  const int writerRank = cdiPioSerialOpenFileMap(streamID);
+  const int writerRank = cdiPioStream2Owner(streamID);
   const int collRank = commInqRankColl();
   const MPI_Comm collComm = commInqCommColl();  // HB: which communicator is to be supplied here?
   const bool reuseRedists
@@ -798,7 +798,7 @@ writeNetCDFStream(size_t streamIdx, struct streamMapping *mapping, void **data_,
       = writeNetCDFStreamSerial;
 #ifdef HAVE_PARALLEL_NC4
   int streamID = openStreams.entries[streamIdx];
-  int rankOpen = cdiPioSerialOpenFileMap(streamID);
+  int rankOpen = cdiPioStream2Owner(streamID);
   if (rankOpen == CDI_PIO_COLLECTIVE_OPEN) writeNetCDFStream_ = writeNetCDFStreamParallel;
 #endif
   writeNetCDFStream_(streamIdx, mapping, data_, currentDataBufSize, conf);
@@ -1382,7 +1382,7 @@ getMaxNumStreamWrites(stream_t *streamptr)
     case CDI_FILETYPE_NC4:
     case CDI_FILETYPE_NC4C:
       {
-        int rank, rankOpen = cdiPioSerialOpenFileMap(streamptr->self);
+        int rank, rankOpen = cdiPioStream2Owner(streamptr->self);
         if (commInqIOMode() == PIO_NONE
 #ifdef HAVE_PARALLEL_NC4
             || rankOpen == CDI_PIO_COLLECTIVE_OPEN
@@ -1424,7 +1424,7 @@ cdiPioServerStreamClose(stream_t *streamptr, int recordBufIsToBeDeleted)
 #ifdef HAVE_LIBNETCDF
         case CDI_FILETYPE_NETCDF:
           {
-            int rank, rankOpen = cdiPioSerialOpenFileMap(streamptr->self);
+            int rank, rankOpen = cdiPioStream2Owner(streamptr->self);
             if (commInqIOMode() == PIO_NONE
 #ifdef HAVE_PARALLEL_NC4
                 || rankOpen == CDI_PIO_COLLECTIVE_OPEN
@@ -1458,7 +1458,7 @@ cdiPioServerStreamClose(stream_t *streamptr, int recordBufIsToBeDeleted)
 static void
 cdiPioCdfDefTimestep(stream_t *streamptr, int tsID)
 {
-  int rank, streamID = streamptr->self, rankOpen = cdiPioSerialOpenFileMap(streamID);
+  int rank, streamID = streamptr->self, rankOpen = cdiPioStream2Owner(streamID);
   if (commInqIOMode() == PIO_NONE
 #ifdef HAVE_PARALLEL_NC4
       || rankOpen == CDI_PIO_COLLECTIVE_OPEN