Add framework for declaration of module parameters

The MXS_MODULE structure now contains a member for parameters. This can be
used by the modules to declare accepted parameters, their types and the
default values. Currently only count, integer, boolean, string and enum
values are supported.

include/maxscale/config.h

@@ -33,6 +33,7 @@
 #include <sys/utsname.h>
 #include <openssl/sha.h>
 #include <maxscale/gw_ssl.h>
+#include <maxscale/modinfo.h>
 
 MXS_BEGIN_DECLS
 
@@ -211,6 +212,64 @@ bool config_is_ssl_parameter(const char *key);
  */
 SSL_LISTENER *make_ssl_structure(CONFIG_CONTEXT *obj, bool require_cert, int *error_count);
 
+/**
+ * @brief Check if a configuration parameter is valid
+ *
+ * If a module has declared parameters and parameters were given to the module,
+ * the given parameters are compared to the expected ones. This function also
+ * does preliminary type checking for various basic values as well as enumerations.
+ *
+ * @param module Module name
+ * @param key Parameter key
+ * @param value Parameter value
+ *
+ * @return True if the configuration parameter is valid
+ */
+bool config_param_is_valid(const char *module, const char *key, const char *value);
+
+/**
+ * @brief Get a boolean value
+ *
+ * @param params List of configuration parameters
+ * @param key Parameter name
+ *
+ * @return The value as a boolean
+ */
+bool config_get_bool(const CONFIG_PARAMETER *params, const char *key);
+
+/**
+ * @brief Get an integer value
+ *
+ * This is used for both MXS_MODULE_PARAM_INT and MXS_MODULE_PARAM_COUNT.
+ *
+ * @param params List of configuration parameters
+ * @param key Parameter name
+ *
+ * @return The integer value of the parameter
+ */
+int config_get_integer(const CONFIG_PARAMETER *params, const char *key);
+
+/**
+ * @brief Get a string value
+ *
+ * @param params List of configuration parameters
+ * @param key Parameter name
+ *
+ * @return The raw string value */
+const char* config_get_string(const CONFIG_PARAMETER *params, const char *key);
+
+/**
+ * @brief Get a enumeration value
+ *
+ * @param params List of configuration parameters
+ * @param key Parameter name
+ *
+ * @return The raw string value
+ *
+ * TODO: Allow multiple enumeration values
+ */
+const char* config_get_enum(const CONFIG_PARAMETER *params, const char *key);
+
 char*               config_clean_string_list(const char* str);
 CONFIG_PARAMETER*   config_clone_param(const CONFIG_PARAMETER* param);
 void                config_enable_feedback_task(void);