nwvolume: allow OS2 namespace with ONE_DEV volumes

When ONE_DEV is active, handles encode the raw inode and cannot also
encode a namespace map index.  Reuse the same device map entry across
namespaces so volumes using both 'o' and 'O' can serve OS/2 namespace
clients.

src/nwvolume.c

@@ -393,8 +393,27 @@ static int look_name_space_map(NW_VOL *v, DEV_NAMESPACE_MAP *dnm,
     int k=-1;
     while (++k < v->maps_count) {
       mp=v->dev_namespace_maps[k];
-      if (mp->dev == dnm->dev && mp->namespace == dnm->namespace)
-        return(k);
+      if (mp->dev == dnm->dev) {
+        /*
+         * VOL_OPTION_ONE_DEV encodes handles as the raw 32-bit inode:
+         *
+         *     handle = inode
+         *
+         * In that mode there is no room in the handle for the dev/namespace
+         * map index.  All namespaces on this one Unix device therefore have
+         * to share the same map entry.  Otherwise a volume with both 'o' and
+         * 'O' set can map the DOS root entry, but later OS/2 namespace lookups
+         * fail with:
+         *
+         *     Cannot map inode=..., dev=..., namespace=4 to vol=... handle
+         *
+         * Non-ONE_DEV volumes keep the old behaviour and still distinguish
+         * mappings by both device and namespace.
+         */
+        if ((v->options & VOL_OPTION_ONE_DEV)
+            || mp->namespace == dnm->namespace)
+          return(k);
+      }
     }
     if (do_insert && v->maps_count < v->max_maps_count) {
       /* now do insert the new map */