.\"     $NetBSD: kthread.9,v 1.7 2002/03/08 23:03:23 kleink Exp $
.\"
.\" Copyright (c) 2000 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.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"        This product includes software developed by the NetBSD
.\"        Foundation, Inc. and its contributors.
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
.\"    contributors may be used to endorse or promote products derived
.\"    from this software without specific prior written permission.
.\"
.\" 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 July 9, 2000
.Dt KTHREAD 9
.Os
.Sh NAME
.Nm kthread_create1 ,
.Nm kthread_exit ,
.Nm kthread_create
.Nd kernel threads
.Sh SYNOPSIS
.Fd #include \*[Lt]sys/kthread.h\*[Gt]
.Ft void
.Fn kthread_create "void (*func)(void *)" "void *arg"
.Ft void
.Fn kthread_exit "int ecode"
.Ft int
.Fn kthread_create1 "void (*func)(void *)" "void *arg" "struct proc **newpp" \
"const char *fmt" "..."
.Sh DESCRIPTION
Kernel threads are light-weight processes which execute entirely
within the kernel.  Any process can request the creation of a new
kernel thread.  Kernel threads are not swapped out during memory
congestion.  The VM space and limits are shared with proc0 (usually swapper).
.Sh FUNCTIONS
.Bl -tag -width compact
.It Fn kthread_create1 "func" "arg" "newpp" "fmt" "..."
Fork a kernel thread.
.Fa newpp
is a pointer the the new proc structure for the kernel thread.
The function
.Fa func
is called with arguments
.Fa arg
to commence execution.
.Fa fmt
is a string containing format information used to display the kernel
thread name.
.It Fn kthread_create "void (*func)(void)" "void *arg"
Register function
.Fa func
to defer creation of the kernel thread.  Deferral of kernel thread
creation is required during system startup when kernel thread resources
are not available.
.It Fn kthread_exit "int ecode"
Exit from a kernel thread.
.El
.Sh RETURN VALUES
Upon successful completion,
.Fn kthread_create1
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.
.It Bq Er EAGAIN
The limit
.Dv RLIMIT_NPROC
on the total number of processes under execution by this
user id would be exceeded.
.El
.Sh CODE REFERENCES
This section describes places within the
.Nx
source tree where actual code implementing or utilising the kthread
framework can be found.  All pathnames are relative to
.Pa /usr/src .
.Pp
The kthread framework itself is implemented within the file
.Pa sys/kern/kern_kthread.c .
Data structures and function prototypes for the framework are located in
.Pa sys/sys/kthread.h .
.Sh SEE ALSO
.Xr driver 9 ,
.Xr fork1 9
.Sh HISTORY
The kthread framework appeared in
.Nx 1.4 .