.\"     $NetBSD: userret.9,v 1.9 2008/04/30 13:10:59 martin Exp $
.\"
.\" Copyright (c) 2002 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Gregory McGarry.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd December 20, 2005
.Dt USERRET 9
.Os
.Sh NAME
.Nm userret
.Nd return path to user-mode execution
.Sh SYNOPSIS
.In sys/lwp.h
.In sys/sched.h
.Ft void
.Fn userret "struct lwp *l"
.Sh DESCRIPTION
The
.Fn userret
function is executed after processing a trap
.Pq e.g., a system call or interrupt
before returning to user-mode execution.
The implementation is machine dependent and is never invoked from
machine-independent code.
The function prototype for each architecture may be different to the
prototype above, however the functionally provided by the
.Fn userret
function on each architecture is essentially the same.
.Pp
Specifically, the
.Fn userret
function performs the following procedure:
.Bl -bullet -offset indent
.It
Detect a change in the signal disposition of the current process and invoke
.Xr postsig 9
to post the signal to the process.
This may occur when the outcome of the trap or syscall posted a signal
to the process
.Pq e.g., invalid instruction trap .
.It
Check the
.Va want_resched
flag to see if the scheduler requires the current process to be
preempted by invoking
.Xr preempt 9
.Pq see Xr cpu_need_resched 9 .
This may occur if the clock interrupt causes the scheduler to
determine that the current process has completed its time slice.
.It
Update the scheduler state.
.El
.Sh SEE ALSO
.Xr cpu_need_resched 9 ,
.Xr postsig 9 ,
.Xr preempt 9 ,
.Xr scheduler 9