Add linker_reference_module().

This function loads a module if required, otherwise bumps the reference
count -- the opposite of linker_file_unload().

sys/kern/kern_linker.c

@@ -331,6 +331,31 @@ out:
     return error;
 }
 
+int
+linker_reference_module(const char *modname, linker_file_t *result)
+{
+    char *pathname;
+    int res;
+
+    /*
+     * There will be a system to look up or guess a file name from
+     * a module name.
+     * For now we just try to load a file with the same name.
+     */
+    if ((pathname = linker_search_path(modname)) == NULL)
+	return (ENOENT);
+
+    /*
+     * If the module is already loaded or built into the kernel,
+     * linker_load_file() simply bumps it's refcount.
+     */
+    res = linker_load_file(pathname, result);
+
+    free(pathname, M_LINKER);
+
+    return (res);
+}
+
 linker_file_t
 linker_find_file_by_name(const char* filename)
 {

sys/sys/linker.h

@@ -106,6 +106,11 @@ int linker_add_class(linker_class_t _cls);
  */
 int linker_load_file(const char* _filename, linker_file_t* _result);
 
+/*
+ * Obtain a reference to a module, loading it if required.
+ */
+int linker_reference_module(const char* _modname, linker_file_t* _result);
+
 /*
  * Find a currently loaded file given its filename.
  */