Provided by: freebsd-manpages_8.2-1_all bug

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 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
     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.