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KPROC(9)	       FreeBSD Kernel Developer's Manual	      KPROC(9)

NAME
     kproc_start, kproc_shutdown, kproc_create,	kproc_exit, kproc_resume,
     kproc_suspend, kproc_suspend_check	-- kernel processes

SYNOPSIS
     #include <sys/kthread.h>

     void
     kproc_start(const void *udata);

     void
     kproc_shutdown(void *arg, int howto);

     int
     kproc_create(void (*func)(void *),	void *arg, struct proc **newpp,
	 int flags, int	pages, const char *fmt,	...);

     void
     kproc_exit(int ecode);

     int
     kproc_resume(struct proc *p);

     int
     kproc_suspend(struct proc *p, int timo);

     void
     kproc_suspend_check(struct	proc *p);

     int
     kproc_kthread_add(void (*func)(void *), void *arg,	struct proc **procptr,
	 struct	thread **tdptr,	int flags, int pages, char * procname,
	 const char *fmt, ...);

DESCRIPTION
     In	FreeBSD	8.0, the kthread*(9) family of functions was renamed to	be the
     kproc*(9) family of functions, as they were misnamed and actually pro-
     duced kernel processes.  A	new family of different	kthread_*(9) functions
     was added to produce real kernel threads.	See the	kthread(9) man page
     for more information on those calls.  Also	note that the
     kproc_kthread_add(9) function appears in both pages as its	functionality
     is	split.

     The function kproc_start()	is used	to start ``internal'' daemons such as
     bufdaemon,	pagedaemon, vmdaemon, and the syncer and is intended to	be
     called from SYSINIT(9).  The udata	argument is actually a pointer to a
     struct kproc_desc which describes the kernel process that should be cre-
     ated:

	   struct kproc_desc {
		   char		   *arg0;
		   void		   (*func)(void);
		   struct proc	   **global_procpp;
	   };

     The structure members are used by kproc_start() as	follows:

	   arg0		  String to be used for	the name of the	process.  This
			  string will be copied	into the p_comm	member of the
			  new process' struct proc.

	   func		  The main function for	this kernel process to run.

	   global_procpp  A pointer to a struct	proc pointer that should be
			  updated to point to the newly	created	process'
			  process structure.  If this variable is NULL,	then
			  it is	ignored.

     The kproc_create()	function is used to create a kernel process.  The new
     process shares its	address	space with process 0, the swapper process, and
     runs in kernel mode only.	The func argument specifies the	function that
     the process should	execute.  The arg argument is an arbitrary pointer
     that is passed in as the only argument to func when it is called by the
     new process.  The newpp pointer points to a struct	proc pointer that is
     to	be updated to point to the newly created process.  If this argument is
     NULL, then	it is ignored.	The flags argument specifies a set of flags as
     described in rfork(2).  The pages argument	specifies the size of the new
     kernel process's stack in pages.  If 0 is used, the default kernel	stack
     size is allocated.	 The rest of the arguments form	a printf(9) argument
     list that is used to build	the name of the	new process and	is stored in
     the p_comm	member of the new process's struct proc.

     The kproc_exit() function is used to terminate kernel processes.  It
     should be called by the main function of the kernel process rather	than
     letting the main function return to its caller.  The ecode	argument spec-
     ifies the exit status of the process.  While exiting, the function
     exit1(9) will initiate a call to wakeup(9)	on the process handle.

     The kproc_resume(), kproc_suspend(), and kproc_suspend_check() functions
     are used to suspend and resume a kernel process.  During the main loop of
     its execution, a kernel process that wishes to allow itself to be sus-
     pended should call	kproc_suspend_check() passing in curproc as the	only
     argument.	This function checks to	see if the kernel process has been
     asked to suspend.	If it has, it will tsleep(9) until it is told to
     resume.  Once it has been told to resume it will return allowing execu-
     tion of the kernel	process	to continue.  The other	two functions are used
     to	notify a kernel	process	of a suspend or	resume request.	 The p argu-
     ment points to the	struct proc of the kernel process to suspend or
     resume.  For kproc_suspend(), the timo argument specifies a timeout to
     wait for the kernel process to acknowledge	the suspend request and	sus-
     pend itself.

     The kproc_shutdown() function is meant to be registered as	a shutdown
     event for kernel processes	that need to be	suspended voluntarily during
     system shutdown so	as not to interfere with system	shutdown activities.
     The actual	suspension of the kernel process is done with kproc_suspend().

     The kproc_kthread_add() function is much like the kproc_create() function
     above except that if the kproc already exists, then only a	new thread
     (see kthread(9)) is created on the	existing process.  The func argument
     specifies the function that the process should execute.  The arg argument
     is	an arbitrary pointer that is passed in as the only argument to func
     when it is	called by the new process.  The	procptr	pointer	points to a
     struct proc pointer that is the location to be updated with the new proc
     pointer if	a new process is created, or if	not NULL, must contain the
     process pointer for the already existing process.	If this	argument
     points to NULL, then a new	process	is created and the field updated.  If
     not NULL, the tdptr pointer points	to a struct thread pointer that	is the
     location to be updated with the new thread	pointer.  The flags argument
     specifies a set of	flags as described in rfork(2).	 The pages argument
     specifies the size	of the new kernel thread's stack in pages.  If 0 is
     used, the default kernel stack size is allocated.	The procname argument
     is	the name the new process should	be given if it needs to	be created.
     It	is NOT a printf	style format specifier but a simple string.  The rest
     of	the arguments form a printf(9) argument	list that is used to build the
     name of the new thread and	is stored in the td_name member	of the new
     thread's struct thread.

RETURN VALUES
     The kproc_create(), kproc_resume(), and kproc_suspend() functions return
     zero on success and non-zero on failure.

EXAMPLES
     This example demonstrates the use of a struct kproc_desc and the func-
     tions kproc_start(), kproc_shutdown(), and	kproc_suspend_check() to run
     the bufdaemon process.

	   static struct proc *bufdaemonproc;

	   static struct kproc_desc buf_kp = {
		   "bufdaemon",
		   buf_daemon,
		   &bufdaemonproc
	   };
	   SYSINIT(bufdaemon, SI_SUB_KTHREAD_BUF, SI_ORDER_FIRST, kproc_start,
	       &buf_kp)

	   static void
	   buf_daemon()
	   {
		   ...
		   /*
		    * This process needs to be suspended prior to shutdown sync.
		    */
		   EVENTHANDLER_REGISTER(shutdown_pre_sync, kproc_shutdown,
		       bufdaemonproc, SHUTDOWN_PRI_LAST);
		   ...
		   for (;;) {
			   kproc_suspend_check(bufdaemonproc);
			   ...
		   }
	   }

ERRORS
     The kproc_resume()	and kproc_suspend() functions will fail	if:

     [EINVAL]		The p argument does not	reference a kernel process.

     The kproc_create()	function will fail if:

     [EAGAIN]		The system-imposed limit on the	total number of	pro-
			cesses under execution would be	exceeded.  The limit
			is given by the	sysctl(3) MIB variable KERN_MAXPROC.

     [EINVAL]		The RFCFDG flag	was specified in the flags parameter.

SEE ALSO
     rfork(2), exit1(9), kthread(9), SYSINIT(9), wakeup(9)

HISTORY
     The kproc_start() function	first appeared in FreeBSD 2.2.	The
     kproc_shutdown(), kproc_create(), kproc_exit(), kproc_resume(),
     kproc_suspend(), and kproc_suspend_check()	functions were introduced in
     FreeBSD 4.0.  Prior to FreeBSD 5.0, the kproc_shutdown(), kproc_resume(),
     kproc_suspend(), and kproc_suspend_check()	functions were named
     shutdown_kproc(), resume_kproc(), shutdown_kproc(), and
     kproc_suspend_loop(), respectively.  Originally they had the names
     kthread_*() but were changed to kproc_*() when real kthreads became
     available.

FreeBSD	10.1		       October 19, 2007			  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | ERRORS | SEE ALSO | HISTORY

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