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MODULE(9)		    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 struc-
     ture  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 han-
     dler, 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),  MOD-
     ULE_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 ports 15.quarterly	November 11, 2021		       MODULE(9)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=module&sektion=9&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>

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