Specifications

CHAPTER 5. IMPLEMENTATION 36

Data Structure

Both data structures ModuleData and ModuleOption are declared in libial mod.h. The

structure ModuleData is slightly shortened compared to the source code.

typedef struct ModuleOption_s {

const char *name;

char value[MAX_BUF];

const char *descr;

} ModuleOption;

typedef struct ModuleData_s {

const char *name;

const char *token;

const char *version;

const char *author;

const char *descr;

ModuleOption *options;

gboolean(*load) (void);

gboolean(*unload) (void);

} ModuleData;

The structure ModuleOption represents a module’s conﬁguration option. The member

name contains the name of the option followed by value in which the option’s value is stored.

It has to be initialized statically with a default value. A description of the option is stored

in descr. As mentioned above, all modules are required to deﬁne an array of ModuleOption

structures. It is essential that the last element of the array is NULL. This is necessary since

the size of the array varies for each module, as it reﬂects the number of the module’s options.

The daemon iterates the ModuleOption using p ointer arithmetic and stops the iteration as

soon as an element with the value NULL is found.

The ﬁrst ﬁve members of the structure ModuleData are strings providing information about

the module. A meaningful name of the module is stored in name, token contains a minimal

name for the module. The member version informs about the module’s version numb er,

author contains the author’s name. The module description is stored in descr. The mem-

ber options is a pointer to the module’s options stored in the already mentioned array of

ModuleOption. The two members load() and unload() are function pointers. The module

has to implement the two functions accordingly. These functions are responsible for loading

and unloading the module, and are invoked by the daemon. The return type of load() and

unload() is gboolean which is not a standard data type of the GNU C Library. It is a data type

provided by GLib and can either be TRUE or FALSE. For example, the array mod options of

the ModuleOption structure, for a module having the two conﬁguration options disable and

verbose, would be implemented by deﬁning: