324 lines
7.7 KiB
Groff
324 lines
7.7 KiB
Groff
.\" Copyright (c) 2000-2001
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" All rights reserved.
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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 DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd October 26, 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_start ,
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.Nm kthread_shutdown ,
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.Nm kthread_add ,
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.Nm kthread_exit ,
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.Nm kthread_resume ,
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.Nm kthread_suspend ,
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.Nm kthread_suspend_check
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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 void
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.Fn kthread_start "const void *udata"
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.Ft void
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.Fn kthread_shutdown "void *arg" "int howto"
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.Ft int
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.Fo kthread_add
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.Fa "void (*func)(void *)" "void *arg" "struct proc *procp"
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.Fa "struct thread **newtdpp" "int flags" "int pages"
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.Fa "const char *fmt" ...
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.Fc
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.Ft void
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.Fn kthread_exit "void"
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.Ft int
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.Fn kthread_resume "struct thread *td"
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.Ft int
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.Fn kthread_suspend "struct thread *td" "int timo"
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.Ft void
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.Fn kthread_suspend_check "struct thread *td"
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.Sh DESCRIPTION
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The function
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.Fn kthread_start
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is used to start
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.Dq internal
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daemons such as
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.Nm bufdaemon , pagedaemon , vmdaemon ,
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and the
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.Nm syncer
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and is intended
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to be called from
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.Xr SYSINIT 9 .
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The
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.Fa udata
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argument is actually a pointer to a
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.Vt "struct kthread_desc"
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which describes the kernel thread that should be created:
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.Bd -literal -offset indent
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struct kthread_desc {
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char *arg0;
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void (*func)(void);
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struct thread **global_threadpp;
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};
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.Ed
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.Pp
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The structure members are used by
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.Fn kthread_start
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as follows:
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.Bl -tag -width ".Va global_threadpp" -offset indent
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.It Va arg0
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String to be used for the name of the thread.
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This string will be copied into the
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.Va td_name
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member of the new threads'
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.Vt "struct thread" .
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.It Va func
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The main function for this kernel thread to run.
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.It Va global_threadpp
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A pointer to a
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.Vt "struct thread"
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pointer that should be updated to point to the newly created thread's
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.Vt thread
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structure.
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If this variable is
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.Dv NULL ,
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then it is ignored.
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The thread will be a subthread of
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.Va proc0
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(PID 0).
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.El
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.Pp
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The
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.Fn kthread_add
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function is used to create a kernel thread.
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The new thread runs in kernel mode only.
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It is added to the process specified by the
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.Fa procp
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argument, or if that is
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.Dv NULL ,
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to
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.Va proc0 .
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The
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.Fa func
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argument specifies the function that the thread should execute.
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The
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.Fa arg
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argument is an arbitrary pointer that is passed in as the only argument to
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.Fa func
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when it is called by the new thread.
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The
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.Fa newtdpp
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pointer points to a
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.Vt "struct thread"
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pointer that is to be updated to point to the newly created thread.
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If this argument is
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.Dv NULL ,
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then it is ignored.
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The
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.Fa flags
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argument specifies a set of flags as described in
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.Xr rfork 2 .
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The
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.Fa pages
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argument specifies the size of the new kernel thread's stack in pages.
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If 0 is used, the default kernel stack size is allocated.
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The rest of the arguments form a
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.Xr printf 9
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argument list that is used to build the name of the new thread and is stored
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in the
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.Va td_name
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member of the new thread's
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.Vt "struct thread" .
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.Pp
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The
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.Fn kthread_exit
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function is used to terminate kernel threads.
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It should be called by the main function of the kernel thread rather than
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letting the main function return to its caller.
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.\" XXX "int ecode" argument isn't documented.
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.Pp
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The
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.Fn kthread_resume ,
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.Fn kthread_suspend ,
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and
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.Fn kthread_suspend_check
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functions are used to suspend and resume a kernel thread.
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During the main loop of its execution, a kernel thread that wishes to allow
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itself to be suspended should call
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.Fn kthread_suspend_check
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passing in
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.Va curthread
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as the only argument.
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This function checks to see if the kernel thread has been asked to suspend.
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If it has, it will
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.Xr tsleep 9
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until it is told to resume.
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Once it has been told to resume it will return allowing execution of the
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kernel thread to continue.
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The other two functions are used to notify a kernel thread of a suspend or
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resume request.
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The
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.Fa td
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argument points to the
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.Vt "struct thread"
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of the kernel thread to suspend or resume.
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For
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.Fn kthread_suspend ,
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the
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.Fa timo
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argument specifies a timeout to wait for the kernel thread to acknowledge the
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suspend request and suspend itself.
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.Pp
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The
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.Fn kthread_shutdown
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function is meant to be registered as a shutdown event for kernel threads that
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need to be suspended voluntarily during system shutdown so as not to interfere
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with system shutdown activities.
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The actual suspension of the kernel thread is done with
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.Fn kthread_suspend .
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.Sh RETURN VALUES
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The
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.Fn kthread_add ,
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.Fn kthread_resume ,
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and
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.Fn kthread_suspend
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functions return zero on success and non-zero on failure.
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.Sh EXAMPLES
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This example demonstrates the use of a
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.Vt "struct kthread_desc"
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and the functions
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.Fn kthread_start ,
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.Fn kthread_shutdown ,
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and
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.Fn kthread_suspend_check
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to run the
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.Nm bufdaemon
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process.
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.Bd -literal -offset indent
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static struct thread *bufdaemonthread;
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static struct kthread_desc buf_kp = {
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"bufdaemon",
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buf_daemon,
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&bufdaemonthread
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};
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SYSINIT(bufdaemon, SI_SUB_KTHREAD_BUF, SI_ORDER_FIRST, kthread_start,
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&buf_kp)
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static void
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buf_daemon()
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{
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...
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/*
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* This process needs to be suspended prior to shutdown sync.
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*/
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EVENTHANDLER_REGISTER(shutdown_pre_sync, kthread_shutdown,
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bufdaemonthread, SHUTDOWN_PRI_LAST);
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...
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for (;;) {
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kthread_suspend_check(bufdaemonthread);
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...
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}
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}
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.Ed
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.Sh ERRORS
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The
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.Fn kthread_resume
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and
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.Fn kthread_suspend
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functions will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa td
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argument does not reference a kernel thread.
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.El
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.Pp
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The
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.Fn kthread_add
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The system-imposed limit on the total
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number of processes under execution would be exceeded.
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The limit is given by the
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.Xr sysctl 3
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MIB variable
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.Dv KERN_MAXPROC .
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.It Bq Er EINVAL
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The
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.Dv RFCFDG
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flag was specified in the
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.Fa flags
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parameter.
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.El
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.Sh SEE ALSO
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.Xr rfork 2 ,
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.Xr exit1 9 ,
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.Xr kproc 9 ,
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.Xr SYSINIT 9 ,
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.Xr wakeup 9
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.Sh HISTORY
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The
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.Fn kthread_start
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function first appeared in
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.Fx 2.2
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where it created a whole process.
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It was converted to create threads in
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.Fx 8.0 .
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The
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.Fn kthread_shutdown ,
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.Fn kthread_exit ,
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.Fn kthread_resume ,
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.Fn kthread_suspend ,
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and
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.Fn kthread_suspend_check
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functions were introduced in
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.Fx 4.0
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and were converted to threads in
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.Fx 8.0 .
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The
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.Fn kthread_create
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call was renamed to
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.Fn kthread_add
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in
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.Fx 8.0 .
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The old functionality of creating a kernel process was renamed
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to
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.Xr kproc_create 9 .
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Prior to
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.Fx 5.0 ,
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the
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.Fn kthread_shutdown ,
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.Fn kthread_resume ,
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.Fn kthread_suspend ,
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and
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.Fn kthread_suspend_check
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functions were named
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.Fn shutdown_kproc ,
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.Fn resume_kproc ,
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.Fn shutdown_kproc ,
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and
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.Fn kproc_suspend_loop ,
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respectively.
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