223 lines
6.8 KiB
Groff
223 lines
6.8 KiB
Groff
.\" $NetBSD: kthread.9,v 1.30 2020/08/01 09:50:42 wiz Exp $
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.\"
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.\" Copyright (c) 2000, 2007, 2008 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, 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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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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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 April 21, 2015
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.Dt KTHREAD 9
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.Os
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.Sh NAME
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.Nm kthread_create ,
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.Nm kthread_exit ,
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.Nm kthread_join ,
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.Nm kthread_fpu_enter ,
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.Nm kthread_fpu_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_exit "int ecode"
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.Ft int
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.Fn kthread_join "lwp_t *l"
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.Ft int
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.Fn kthread_fpu_enter
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.Ft void
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.Fn kthread_fpu_exit "int s"
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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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.Pp
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If the machine has any per-CPU floating-point units or SIMD vector
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units that are normally available to user threads, they can be used by
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kthreads between
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.Fn kthread_fpu_enter
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and
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.Fn kthread_fpu_exit .
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.Sh FUNCTIONS
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.Bl -tag -width compact
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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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.It Fa ci
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If
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.No non- Ns Dv NULL ,
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the thread will be created bound to the CPU specified 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 Fa arg
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An argument to be passed to
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.Fn func .
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May be
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.Dv NULL
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if not required.
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.It Fa newlp
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A pointer to receive the new LWP structure for the kernel thread.
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May be
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.Dv NULL ,
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unless
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.Dv KTHREAD_MUSTJOIN
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is specified in
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.Fa flags .
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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
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.Dv NULL .
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.El
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.Pp
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The following
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.Va flags
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are defined.
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.Bl -tag -width KTHREAD_MUSTJOIN
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.It 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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.It 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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.It 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 Dv KTHREAD_TS
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Causes the kthread to be created in the
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.Dv SCHED_OTHER
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class (timeshared).
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The thread's priority will be dynamically adjusted by the scheduler.
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Increased activity by the kthread will cause its priority to fall;
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decreased activity will cause its priority to rise.
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By default, kthreads are created in the
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.Dv SCHED_RR
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class, with a fixed
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priority specified by
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.Ar pri .
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Threads in the
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.Dv SCHED_RR
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class do not have their priority dynamically
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adjusted by the scheduler.
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.It Dv KTHREAD_MUSTJOIN
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Indicates that created kthread must be joined.
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In such case
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.Fn kthread_exit
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will wait until
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.Fn kthread_join
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will be called.
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.El
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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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.It Fn kthread_join "l"
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Suspend execution of calling thread until the target kthread terminates.
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Conceptually the function can be compared to the user space
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.Xr pthread_join 3 ,
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however it must be called only once for kernel thread which was
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created using the
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.Dv KTHREAD_MUSTJOIN
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flag and would wait on
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.Fa kthread_exit .
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.It Fn kthread_fpu_enter
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Allow the current kthread to use any machine-dependent per-CPU
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floating-point units or SIMD vector units normally available to user
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threads.
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Returns a cookie that must be passed to
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.Fn kthread_fpu_exit
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when done.
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.Pp
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Matching pairs of
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.Fn kthread_fpu_enter
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and
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.Fn kthread_fpu_exit
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may be nested.
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.It Fn kthread_fpu_exit "s"
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Restore the current kthread's access to machine-dependent per-CPU
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floating-point units or SIMD vector units to what it was before the
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call to
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.Fn kthread_fpu_enter
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that returned
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.Fa s .
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.Pp
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On the last
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.Fn kthread_fpu_exit ,
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zero all the units' registers to avoid leaking secrets \(em such units
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are often used for cryptography.
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.El
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.Sh RETURN VALUES
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Upon successful completion,
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.Fn kthread_create
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returns 0.
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Otherwise, the following error values are returned:
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.Bl -tag -width [EAGAIN]
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.It Bq Er EAGAIN
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The limit on the total number of system processes would be exceeded;
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or the limit
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.Dv RLIMIT_NPROC
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on the total number of processes under execution by this
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user id would be exceeded.
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.El
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.Sh CODE REFERENCES
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The kthread framework itself is implemented within the file
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.Pa sys/kern/kern_kthread.c .
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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 condvar 9 ,
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.Xr driver 9 ,
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.Xr softint 9 ,
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.Xr workqueue 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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