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.