kthread_create

KPROC(9)                    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 produced
     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
     created:

           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 specifies 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 suspended
     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 execution 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 argument 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 suspend 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 functions
     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
                        processes 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.

                                October 19, 2007