MODULE(9)              FreeBSD Kernel Developer's Manual             MODULE(9)

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.  If the event
     handler function is NULL, the module will use a no-operation function
     handler instead.

     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_PNP_INFO(9), MODULE_VERSION(9), SYSCALL_MODULE(9)

     /usr/share/examples/kld

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

FreeBSD 13.1-RELEASE-p6        November 11, 2021       FreeBSD 13.1-RELEASE-p6