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.\" $NetBSD: kthread.9,v 1.14 2005/09/10 22:21:41 wiz Exp $
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.\" $NetBSD: kthread.9,v 1.15 2007/07/14 11:22:33 ad Exp $
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.\"
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.\" Copyright (c) 2000 The NetBSD Foundation, Inc.
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.\" Copyright (c) 2000, 2007 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Gregory McGarry.
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.\" by Gregory McGarry, and by Andrew Doran.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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@ -34,60 +34,95 @@
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd August 27, 2005
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.Dd July 14, 2007
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.Dt KTHREAD 9
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.Os
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.Sh NAME
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.Nm kthread_create1 ,
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.Nm kthread_exit ,
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.Nm kthread_create
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.Nm kthread_create ,
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.Nm kthread_destroy ,
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.Nm kthread_exit
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.Nd kernel threads
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.Sh SYNOPSIS
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.In sys/kthread.h
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.Ft int
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.Fn kthread_create "pri_t pri" "int flags" "struct cpu_info *ci" \
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"void (*func)(void *)" "void *arg" "lwp_t **newlp" "const char *fmt" "..."
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.Ft void
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.Fn kthread_create "void (*func)(void *)" "void *arg"
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.Fn kthread_destroy "lwp_t *l"
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.Ft void
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.Fn kthread_exit "int ecode"
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.Ft int
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.Fn kthread_create1 "void (*func)(void *)" "void *arg" "struct proc **newpp" \
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"const char *fmt" "..."
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.Sh DESCRIPTION
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Kernel threads are light-weight processes which execute entirely
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within the kernel.
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.Pp
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Any process can request the creation of a new kernel thread.
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Kernel threads are not swapped out during memory congestion.
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The VM space and limits are shared with proc0 (usually swapper).
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A kernel thread must call
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.Fn kthread_exit
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to end execution.
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.Sh FUNCTIONS
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.Bl -tag -width compact
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.It Fn kthread_create1 "void (*func)(void *)" "void *arg" "struct proc **newpp" "const char *fmt" "..."
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Fork a kernel thread.
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.Fa newpp
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is a pointer the new proc structure for the kernel thread.
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The function
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.Fa func
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is called with arguments
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.Fa arg
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to commence execution.
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.Fa fmt
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is a string containing format information used to display the kernel
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thread name.
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The function
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.Fa func
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must not return.
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If the kernel thread runs to completion, it must call
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.It Fn kthread_create "pri" "flags" "ci" "func" "arg" "newlp" "fmt" "..."
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Create a kernel thread.
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The arguments are as follows.
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.Bl -tag -width compact
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.It Fa pri
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Priority level for the thread.
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If no priority level is desired specify
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.Dv PRI_NONE ,
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causing
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.Fn kthread_create
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to select the default priority level.
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.It Fa flags
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Flags that can be logically ORed together to alter the thread's behaviour.
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.Pp
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.Dv KTHREAD_IDLE :
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causes the thread to be created in the
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.Dv LSIDL
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(idle) state.
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By default, the threads are created in the
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.Dv LSRUN
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(runnable) state, meaning they will begin execution shortly after creation.
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.Pp
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.Dv KTHREAD_MPSAFE :
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Specifies that the thread does its own locking and so is multiprocessor safe.
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If not specified, the global kernel lock will be held whenever the thread is
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running (unless explicitly dropped by the thread).
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.Pp
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.Dv KTHREAD_INTR :
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Specifies that the thread services device interrupts.
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This flag is intended for kernel internal use and should not normally be
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specified.
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.It Fa ci
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If non-NULL, the thread will be created bound to the CPU specified
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by
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.Fa ci ,
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meaning that it will only ever execute on that CPU.
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By default, the threads are free to execute on any CPU in the system.
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.It Fa func
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A function to be called when the thread begins executing.
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This function must not return.
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If the thread runs to completion, it must call
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.Fn kthread_exit
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to properly terminate itself.
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.It Fn kthread_create "void (*func)(void *)" "void *arg"
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Register function
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.Fa func
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to defer creation of the kernel thread.
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Deferral of kernel thread creation is required during system startup
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when kernel thread resources are not available.
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.It Fn kthread_exit "int ecode"
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.It Fa arg
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An argument to be passed to
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.Fn func .
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May be NULL if not required.
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.It Fa newpl
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A pointer to receive the new lwp structure for the kernel thread.
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May be NULL if not required.
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.It Fa fmt
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A string containing format information used to display the kernel
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thread name.
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Must not be NULL.
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.El
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.It Fn kthread_destroy "l"
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From another thread executing in the kernel, cause a kthread to exit.
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The kthread must be in the
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.Dv LSIDL
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(idle) state.
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.It Fn kthread_exit "ecode"
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Exit from a kernel thread.
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Must only be called by a kernel thread.
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.El
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.Sh RETURN VALUES
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Upon successful completion,
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@ -116,8 +151,7 @@ The kthread framework itself is implemented within the file
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Data structures and function prototypes for the framework are located in
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.Pa sys/sys/kthread.h .
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.Sh SEE ALSO
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.Xr driver 9 ,
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.Xr fork1 9
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.Xr driver 9
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.Sh HISTORY
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The kthread framework appeared in
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.Nx 1.4 .
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