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.\" $OpenBSD: kthread.9,v 1.10 2013/11/18 20:21:50 deraadt Exp $
.\"
.\" Copyright (c) 1999 Marc Espie
.\" All rights reserved.
.\"
.\" 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 AUTHOR ``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 AUTHOR 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 $Mdocdate: November 18 2013 $
.Dt KTHREAD 9
.Os
.Sh NAME
.Nm kthread_create ,
.Nm kthread_exit ,
.Nm kthread_create_deferred
.Nd kernel threads
.Sh SYNOPSIS
.In sys/kthread.h
.Ft int
.Fn kthread_create "void (*func)(void *)" "void *arg" "struct proc **newpp" "const char *name"
.Ft void
.Fn kthread_exit "int ecode"
.Ft void
.Fn kthread_create_deferred "void (*func)(void *)" "void *arg"
.Sh DESCRIPTION
Kernel threads are system light-weight processes: cloned from process 0
(the swapper), sharing its memory map and limits, but with a copy of its
file descriptor table.
They don't receive broadcast nor group signals and they can't be swapped.
.Pp
Any process can call
.Fn kthread_create
to create a kernel thread.
The new process starts up executing
.Fa func
with argument
.Fa arg .
If
.Fa newpp
is not
.Dv NULL ,
it is filled with the address of the new process.
.Fa name
is used to name the process.
.Pp
A kernel thread will terminate by calling
.Fn kthread_exit ,
with exit code
.Fa ecode .
.Pp
Since the system has to be up and running for creating
new processes, device drivers that want to create kernel threads early
(e.g., at attach time) may use
.Fn kthread_create_deferred
instead.
The system will call back the function
.Fa func
with argument
.Fa arg
when it can create threads, so it is up to
.Fa func
to call
.Fn kthread_create
at that point.
.Sh RETURN VALUES
Upon successful completion,
.Fn kthread_create
returns 0.
Otherwise, the following error values are returned:
.Bl -tag -width [EAGAIN]
.It Bq Er EAGAIN
The limit on the total number of system processes would be exceeded.
.El
.Sh SEE ALSO
.Xr fork1 9
.Sh BUGS
There is currently no way to use
.Va ecode
to any sensible purpose from
.Fn kthread_exit .
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