Because this error comes up over and over and over and over and ...

Libltdl erroneously returns an error string of "file not found" for
lots of reasons, even if the file really *is* there, but just failed
to dlopen() for some reason.  So if lt_dlerror() returns "file not
found", do some simple hueristics and if we *do* find a file, print a
slightly better error message.

This commit was SVN r21214.

opal/mca/base/mca_base_component_find.c

@@ -24,6 +24,12 @@
 #include <string.h>
 #include <ctype.h>
 #include <stdlib.h>
+#ifdef HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif
+#ifdef HAVE_SYS_STAT_H
+#include <sys/stat.h>
+#endif
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
 #endif
@@ -359,6 +365,26 @@ static int save_filename(const char *filename, lt_ptr data)
 }
 
 
+static int file_exists(const char *filename, const char *ext)
+{
+    char *final;
+    struct stat buf;
+    int ret;
+
+    if (NULL != ext) {
+        asprintf(&final, "%s.%s", filename, ext);
+    } else {
+        final = strdup(filename);
+    }
+    if (NULL == final) {
+        return 0;
+    }
+    ret = stat(final, &buf);
+    free(final);
+    return (0 == ret ? 1 : 0);
+}
+
+
 /*
  * Open a component, chasing down its dependencies first, if possible.
  */
@@ -428,6 +454,20 @@ static int open_component(component_file_item_t *target_file,
 #endif
   if (NULL == component_handle) {
     err = strdup(lt_dlerror());
+    /* Because libltdl erroneously says "file not found" for any type
+       of error -- which is especially misleading when the file is
+       actually there but cannot be opened for some other reason
+       (e.g., missing symbol) -- do some simple huersitics and if the
+       file [probably] does exist, print a slightly better error
+       message. */
+    if (0 == strcmp("file not found", err) &&
+        (file_exists(target_file->filename, "lo") ||
+         file_exists(target_file->filename, "so") ||
+         file_exists(target_file->filename, "dylib") ||
+         file_exists(target_file->filename, "dll"))) {
+        free(err);
+        err = strdup("perhaps a missing symbol, or compiled for a different version of Open MPI?");
+    }
     opal_output_verbose(vl, 0, "mca: base: component_find: unable to open %s: %s (ignored)", 
                         target_file->filename, err);
     free(err);