.\"     $NetBSD: kthread.9,v 1.14 2005/09/10 22:21:41 wiz Exp $
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.Dd August 27, 2005
.Dt KTHREAD 9
.Os
.Sh NAME
.Nm kthread_create1 ,
.Nm kthread_exit ,
.Nm kthread_create
.Nd kernel threads
.Sh SYNOPSIS
.In sys/kthread.h
.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).
A kernel thread must call
.Fn kthread_exit
to end execution.
.Sh FUNCTIONS
.Bl -tag -width compact
.It Fn kthread_create1 "void (*func)(void *)" "void *arg" "struct proc **newpp" "const char *fmt" "..."
Fork a kernel thread.
.Fa newpp
is a pointer 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.
The function
.Fa func
must not return.
If the kernel thread runs to completion, it must call
.Fn kthread_exit
to properly terminate itself.
.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 using 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 .