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.Dd November 11, 2021
.Dt MODULE 9
.Os
.Sh NAME
.Nm module
.Nd structure describing a kernel module
.Sh DESCRIPTION
Each module in the kernel is described by a
.Vt 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
.Dv NULL ,
the module will use a no-operation function handler instead.
.Pp
The
.Xr DECLARE_MODULE 9
macro
registers the module with the system.
.Pp
When the module is loaded, the event handler function is called with
the
.Fa what
argument set to
.Dv MOD_LOAD .
.Pp
On unload it is first called with
.Fa what
set to
.Dv MOD_QUIESCE .
If the unload was not forced, a non-zero return will prevent the
unload from happening.
.Pp
If the unload continues
.Fa what
is set to
.Dv MOD_UNLOAD .
If the module returns non-zero to this, the unload will not happen.
.Pp
The difference between
.Dv MOD_QUIESCE
and
.Dv MOD_UNLOAD
is that the module should fail
.Dv MOD_QUIESCE
if it is currently in use, whereas
.Dv 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.
.Pp
When the system is shutting down,
.Fa what
contains the value of
.Dv MOD_SHUTDOWN .
.Pp
The module should return
.Er EOPNOTSUPP
for unsupported and unrecognized values of
.Fa what .
.Sh EXAMPLES
.Bd -literal
#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);
.Ed
.Sh SEE ALSO
.Xr DECLARE_MODULE 9 ,
.Xr DEV_MODULE 9 ,
.Xr DRIVER_MODULE 9 ,
.Xr MODULE_DEPEND 9 ,
.Xr MODULE_PNP_INFO 9 ,
.Xr MODULE_VERSION 9 ,
.Xr SYSCALL_MODULE 9
.Pp
.Pa /usr/share/examples/kld
.Sh AUTHORS
This manual page was written by
.An Alexander Langer Aq Mt alex@FreeBSD.org .