.\"	$OpenBSD: startuphook_establish.9,v 1.5 2007/05/31 19:20:01 jmc Exp $
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.Dd $Mdocdate: May 31 2007 $
.Dt STARTUPHOOK_ESTABLISH 9
.Os
.Sh NAME
.Nm startuphook_establish ,
.Nm startuphook_disestablish
.Nd add or remove a startup hook
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/systm.h>
.Ft void *
.Fn startuphook_establish "void (*fn)(void *)" "void *arg"
.Ft void
.Fn startuphook_disestablish "void *cookie"
.Sh DESCRIPTION
The
.Fn startuphook_establish
function adds
.Fa fn
to the list of hooks invoked by
.Xr dostartuphooks 9
at startup.
When invoked, the hook function
.Fa fn
will be passed
.Fa arg
as its only argument.
.Pp
The
.Fn startuphook_disestablish
function removes the hook described by the opaque pointer
.Fa cookie
from the list of hooks to be invoked at startup.
If
.Fa cookie
is invalid, the result of
.Fn startuphook_disestablish
is undefined.
.Pp
Startup hooks should be used to perform one-time activities
that must happen immediately before the root and swap devices
are configured, but after normal device autoconfiguration.
.Pp
Startup hooks are, like shutdown hooks, implemented via the more general
.Xr dohooks 9
API.
.Sh RETURN VALUES
If successful,
.Fn startuphook_establish
returns an opaque pointer describing the newly established
startup hook.
Otherwise, it returns
.Dv NULL .
.Sh EXAMPLES
It may be appropriate to use a startup hook to provide potential root or
swap devices that have delayed configuration.
The
.Xr iop 4
shows an example of this usage.
.Sh SEE ALSO
.Xr dohooks 9 ,
.Xr doshutdownhooks 9 ,
.Xr dostartuphooks 9
.Sh BUGS
The names are clumsy, at best.