kproc_shutdown man page on FreeBSD

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KPROC(9)		 BSD 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 exisiting 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 argu‐
     ment specifies a set of flags as described in rfork(2).  The pages argu‐
     ment 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 argu‐
     ment is the name the new process should be given if it needs to be cre‐
     ated.  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.

BSD			       October 19, 2007				   BSD
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