1.\" $NetBSD: userret.9,v 1.9 2008/04/30 13:10:59 martin Exp $ 2.\" 3.\" Copyright (c) 2002 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Gregory McGarry. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd December 20, 2005 31.Dt USERRET 9 32.Os 33.Sh NAME 34.Nm userret 35.Nd return path to user-mode execution 36.Sh SYNOPSIS 37.In sys/lwp.h 38.In sys/sched.h 39.Ft void 40.Fn userret "struct lwp *l" 41.Sh DESCRIPTION 42The 43.Fn userret 44function is executed after processing a trap 45.Pq e.g., a system call or interrupt 46before returning to user-mode execution. 47The implementation is machine dependent and is never invoked from 48machine-independent code. 49The function prototype for each architecture may be different to the 50prototype above, however the functionally provided by the 51.Fn userret 52function on each architecture is essentially the same. 53.Pp 54Specifically, the 55.Fn userret 56function performs the following procedure: 57.Bl -bullet -offset indent 58.It 59Detect a change in the signal disposition of the current process and invoke 60.Xr postsig 9 61to post the signal to the process. 62This may occur when the outcome of the trap or syscall posted a signal 63to the process 64.Pq e.g., invalid instruction trap . 65.It 66Check the 67.Va want_resched 68flag to see if the scheduler requires the current process to be 69preempted by invoking 70.Xr preempt 9 71.Pq see Xr cpu_need_resched 9 . 72This may occur if the clock interrupt causes the scheduler to 73determine that the current process has completed its time slice. 74.It 75Update the scheduler state. 76.El 77.Sh SEE ALSO 78.Xr cpu_need_resched 9 , 79.Xr postsig 9 , 80.Xr preempt 9 , 81.Xr scheduler 9 82