src/plugin.c: Print a more verbose error message if lt_dlopen() fails.

Since the Debian package doesn't depend on the libraries used by the
collectd plugins, some plugins may fail to load. ltdl reports this with
the very confusing error message "file not found". Since the plugin is
in fact available, many users don't realize a dependency is missing and
assume collectd is looking in the wrong directory -- and they are hardly
to blame for this.

This commit introduces a lengthy error message which hopefully points
users into the right direction.

diff --git a/src/plugin.c b/src/plugin.c
index 307bbf4..492be21 100644 (file)
--- a/src/plugin.c
+++ b/src/plugin.c
@@ -279,8 +279,6 @@ static int plugin_load_file (char *file, uint32_t flags)
        lt_dlhandle dlh;
        void (*reg_handle) (void);
 
-       DEBUG ("file = %s", file);
-
        lt_dlinit ();
        lt_dlerror (); /* clear errors */
 
@@ -296,23 +294,35 @@ static int plugin_load_file (char *file, uint32_t flags)
        }
 #else /* if LIBTOOL_VERSION == 1 */
        if (flags & PLUGIN_FLAGS_GLOBAL)
-               ERROR ("plugin_load_file: The global flag is not supported, "
+               WARNING ("plugin_load_file: The global flag is not supported, "
                                "libtool 2 is required for this.");
        dlh = lt_dlopen (file);
 #endif
 
        if (dlh == NULL)
        {
-               const char *error = lt_dlerror ();
+               char errbuf[1024] = "";
+
+               ssnprintf (errbuf, sizeof (errbuf),
+                               "lt_dlopen (\"%s\") failed: %s. "
+                               "The most common cause for this problem are "
+                               "missing dependencies. Use ldd(1) to check "
+                               "the dependencies of the plugin "
+                               "/ shared object.",
+                               file, lt_dlerror ());
+
+               ERROR ("%s", errbuf);
+               /* Make sure this is printed to STDERR in any case, but also
+                * make sure it's printed only once. */
+               if (list_log != NULL)
+                       fprintf (stderr, "ERROR: %s\n", errbuf);
 
-               ERROR ("lt_dlopen (%s) failed: %s", file, error);
-               fprintf (stderr, "lt_dlopen (%s) failed: %s\n", file, error);
                return (1);
        }
 
        if ((reg_handle = (void (*) (void)) lt_dlsym (dlh, "module_register")) == NULL)
        {
-               WARNING ("Couldn't find symbol `module_register' in `%s': %s\n",
+               WARNING ("Couldn't find symbol \"module_register\" in \"%s\": %s\n",
                                file, lt_dlerror ());
                lt_dlclose (dlh);
                return (-1);