.\"     $NetBSD: userret.9,v 1.8 2007/02/17 17:29:24 yamt Exp $
.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Gregory McGarry.
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.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