1.\" $NetBSD: kthread.9,v 1.16 2007/11/21 23:11:06 xtraeme Exp $ 2.\" 3.\" Copyright (c) 2000, 2007 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, and by Andrew Doran. 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.\" 3. All advertising materials mentioning features or use of this software 18.\" must display the following acknowledgement: 19.\" This product includes software developed by the NetBSD 20.\" Foundation, Inc. and its contributors. 21.\" 4. Neither the name of The NetBSD Foundation nor the names of its 22.\" contributors may be used to endorse or promote products derived 23.\" from this software without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 26.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 27.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 28.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 29.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 30.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 31.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 32.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 33.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 34.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 35.\" POSSIBILITY OF SUCH DAMAGE. 36.\" 37.Dd November 22, 2007 38.Dt KTHREAD 9 39.Os 40.Sh NAME 41.Nm kthread_create , 42.Nm kthread_destroy , 43.Nm kthread_exit 44.Nd kernel threads 45.Sh SYNOPSIS 46.In sys/kthread.h 47.Ft int 48.Fn kthread_create "pri_t pri" "int flags" "struct cpu_info *ci" \ 49"void (*func)(void *)" "void *arg" "lwp_t **newlp" "const char *fmt" "..." 50.Ft void 51.Fn kthread_destroy "lwp_t *l" 52.Ft void 53.Fn kthread_exit "int ecode" 54.Sh DESCRIPTION 55Kernel threads are light-weight processes which execute entirely 56within the kernel. 57.Pp 58Any process can request the creation of a new kernel thread. 59Kernel threads are not swapped out during memory congestion. 60The VM space and limits are shared with proc0 (usually swapper). 61.Sh FUNCTIONS 62.Bl -tag -width compact 63.It Fn kthread_create "pri" "flags" "ci" "func" "arg" "newlp" "fmt" "..." 64Create a kernel thread. 65The arguments are as follows. 66.Bl -tag -width compact 67.It Fa pri 68Priority level for the thread. 69If no priority level is desired specify 70.Dv PRI_NONE , 71causing 72.Fn kthread_create 73to select the default priority level. 74.It Fa flags 75Flags that can be logically ORed together to alter the thread's behaviour. 76.Pp 77.Dv KTHREAD_IDLE : 78causes the thread to be created in the 79.Dv LSIDL 80(idle) state. 81By default, the threads are created in the 82.Dv LSRUN 83(runnable) state, meaning they will begin execution shortly after creation. 84.Pp 85.Dv KTHREAD_MPSAFE : 86Specifies that the thread does its own locking and so is multiprocessor safe. 87If not specified, the global kernel lock will be held whenever the thread is 88running (unless explicitly dropped by the thread). 89.Pp 90.Dv KTHREAD_INTR : 91Specifies that the thread services device interrupts. 92This flag is intended for kernel internal use and should not normally be 93specified. 94.It Fa ci 95If non-NULL, the thread will be created bound to the CPU specified 96by 97.Fa ci , 98meaning that it will only ever execute on that CPU. 99By default, the threads are free to execute on any CPU in the system. 100.It Fa func 101A function to be called when the thread begins executing. 102This function must not return. 103If the thread runs to completion, it must call 104.Fn kthread_exit 105to properly terminate itself. 106.It Fa arg 107An argument to be passed to 108.Fn func . 109May be NULL if not required. 110.It Fa newpl 111A pointer to receive the new lwp structure for the kernel thread. 112May be NULL if not required. 113.It Fa fmt 114A string containing format information used to display the kernel 115thread name. 116Must not be NULL. 117.El 118.It Fn kthread_destroy "l" 119From another thread executing in the kernel, cause a kthread to exit. 120The kthread must be in the 121.Dv LSIDL 122(idle) state. 123.It Fn kthread_exit "ecode" 124Exit from a kernel thread. 125Must only be called by a kernel thread. 126.El 127.Sh RETURN VALUES 128Upon successful completion, 129.Fn kthread_create 130returns 0. 131Otherwise, the following error values are returned: 132.Bl -tag -width [EAGAIN] 133.It Bq Er EAGAIN 134The limit on the total number of system processes would be exceeded. 135.It Bq Er EAGAIN 136The limit 137.Dv RLIMIT_NPROC 138on the total number of processes under execution by this 139user id would be exceeded. 140.El 141.Sh CODE REFERENCES 142This section describes places within the 143.Nx 144source tree where actual code implementing or using the kthread 145framework can be found. 146All pathnames are relative to 147.Pa /usr/src . 148.Pp 149The kthread framework itself is implemented within the file 150.Pa sys/kern/kern_kthread.c . 151Data structures and function prototypes for the framework are located in 152.Pa sys/sys/kthread.h . 153.Sh SEE ALSO 154.Xr driver 9 155.Sh HISTORY 156The kthread framework appeared in 157.Nx 1.4 . 158