NAME

     module — structure describing a kernel module

DESCRIPTION

     Each module in the kernel is described by a module_t structure.  The structure contains the
     name of the device, a unique ID number, a pointer to an event handler function and to an
     argument, which is given to the event handler, as well as some kernel internal data.

     The DECLARE_MODULE(9) macro registers the module with the system.

     When the module is loaded, the event handler function is called with the what argument set
     to MOD_LOAD.

     On unload it is first called with what set to MOD_QUIESCE.  If the unload was not forced, a
     non-zero return will prevent the unload from happening.

     If the unload continues what is set to MOD_UNLOAD.  If the module returns non-zero to this,
     the unload will not happen.

     The difference between MOD_QUIESCE and MOD_UNLOAD is that the module should fail MOD_QUIESCE
     if it is currently in use, whereas MOD_UNLOAD should only fail if it is impossible to unload
     the module, for instance because there are memory references to the module which cannot be
     revoked.

     When the system is shutting down, what contains the value of MOD_SHUTDOWN.

     The module should return EOPNOTSUPP for unsupported and unrecognized values of what.

EXAMPLES

     #include <sys/param.h>
     #include <sys/kernel.h>
     #include <sys/module.h>

     static int foo_handler(module_t mod, int /*modeventtype_t*/ what,
                            void *arg);

     static moduledata_t mod_data= {
             "foo",
             foo_handler,
             NULL
     };

     MODULE_VERSION(foo, 1);
     MODULE_DEPEND(foo, bar, 1, 3, 4);

     DECLARE_MODULE(foo, mod_data, SI_SUB_EXEC, SI_ORDER_ANY);

SEE ALSO

     DECLARE_MODULE(9), DEV_MODULE(9), DRIVER_MODULE(9), MODULE_DEPEND(9), MODULE_VERSION(9),
     SYSCALL_MODULE(9)

     /usr/share/examples/kld

AUTHORS

     This manual page was written by Alexander Langer <alex@FreeBSD.org>.