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KTHREAD (9) | Kernel routines | Unix Manual Pages | :man


kproc_start, kproc_shutdown, kthread_create, kthread_exit, kthread_resume, kthread_suspend, kthread_suspend_check - kernel threads


Return Values
See Also


.In sys/kthread.h void kproc_start "const void *udata" void kproc_shutdown "void *arg" "int howto" int kthread_create "void (*func)(void *)" "void *arg" "struct proc **newpp" "int flags" "int pages" "const char *fmt" "..." void kthread_exit "int ecode" int kthread_resume "struct proc *p" int kthread_suspend "struct proc *p" "int timo" void kthread_suspend_check "struct proc *p"


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 thread 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 kthread_create function is used to create a kernel thread. The new thread shares its address space with process 0, the swapper process, and runs in kernel mode only. The func argument specifies the function that the thread 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 thread’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 thread and is stored in the p_comm member of the new thread’s struct proc.

The kthread_exit function is used to terminate kernel threads. It should be called by the main function of the kernel thread rather than letting the main function return to its caller. The ecode argument specifies the exit status of the thread. While exiting, the function exit1(9) will initiate a call to wakeup(9) on the thread handle.

The kthread_resume, kthread_suspend, and kthread_suspend_check functions are used to suspend and resume a kernel thread. During the main loop of its execution, a kernel thread that wishes to allow itself to be suspended should call kthread_suspend_check passing in curproc as the only argument. This function checks to see if the kernel thread 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 thread to continue. The other two functions are used to notify a kernel thread of a suspend or resume request. The p argument points to the struct proc of the kernel thread to suspend or resume. For kthread_suspend, the timo argument specifies a timeout to wait for the kernel thread to acknowledge the suspend request and suspend itself.

The kproc_shutdown function is meant to be registered as a shutdown event for kernel threads that need to be suspended voluntarily during system shutdown so as not to interfere with system shutdown activities. The actual suspension of the kernel thread is done with kthread_suspend.


The kthread_create, kthread_resume, and kthread_suspend functions return zero on success and non-zero on failure.


This example demonstrates the use of a struct kproc_desc and the functions kproc_start, kproc_shutdown, and kthread_suspend_check to run the "bufdaemon" process.
static struct proc *bufdaemonproc;

static struct kproc_desc buf_kp = {

static void
* This process needs to be suspended prior to shutdown sync.
EVENTHANDLER_REGISTER(shutdown_pre_sync, kproc_shutdown,
bufdaemonproc, SHUTDOWN_PRI_LAST);
for (;;) {


The kthread_resume and kthread_suspend functions will fail if:
The p argument does not reference a kernel thread.

The kthread_create function will fail if:

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.
The RFCFDG flag was specified in the flags parameter.


rfork(2), exit1(9), SYSINIT(9), wakeup(9)


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