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DESCRIPTION

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:

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.

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);
		...
	}
}