usnic: show_help if we can't create the connectivity map file

QA ran across the case where the user can't write to the target
directory for the connectivity map file.  In this case, we silently
continued.  They requested that we at least warn in this case.

Fixes Cisco bug CSCup62821

Reviewed by Dave Goodell

cmr=v1.8.2:reviewer=ompi-rm1.8

This commit was SVN r32283.

ompi/mca/btl/usnic/btl_usnic_map.c

@@ -10,6 +10,10 @@
 #include "ompi_config.h"
 
 #include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "opal/util/show_help.h"
 
 #include "btl_usnic.h"
 #include "btl_usnic_util.h"
@@ -246,7 +250,15 @@ void ompi_btl_usnic_connectivity_map(void)
 
     fp = fopen(filename, "w");
     if (NULL == fp) {
-        /* JMS abort? */
+        char dirname[PATH_MAX];
+        getcwd(dirname, sizeof(dirname));
+        dirname[sizeof(dirname) - 1] = '\0';
+        opal_show_help("help-mpi-btl-usnic.txt", "cannot write to map file",
+                       true,
+                       ompi_process_info.nodename,
+                       filename,
+                       dirname,
+                       strerror(errno), errno);
         return;
     }
 

ompi/mca/btl/usnic/help-mpi-btl-usnic.txt

@@ -282,3 +282,13 @@ may exist for other peer pairs, too.
 
 NOTE: You can set the MCA param btl_usnic_show_route_failures to 0 to
 disable this warning.
+#
+[cannot write to map file]
+WARNING: The usnic BTL was unable to open the requested output
+connectivity map file.  Your job will continue, but this output
+connectivity map file will not be written.
+
+  Local server:      %s
+  Output map file:   %s
+  Working directory: %s
+  Error:             %s (%d)