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kthread_create.9freebsd

BSD mandoc

NAME

kproc_start kproc_shutdown kthread_create kthread_exit kthread_resume kthread_suspend kthread_suspend_check - kernel threads

SYNOPSIS

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

DESCRIPTION

The function Fn 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 Fa 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 Fn 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 Fn 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 Fa func argument specifies the function that the thread should execute. The Fa arg argument is an arbitrary pointer that is passed in as the only argument to Fa func when it is called by the new process. The Fa 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 Fa flags argument specifies a set of flags as described in rfork(2). The Fa 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 Fn 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 Fa 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 Fn kthread_resume , Fn kthread_suspend , and Fn 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 Fn 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 Fa p argument points to the struct proc of the kernel thread to suspend or resume. For Fn kthread_suspend , the Fa timo argument specifies a timeout to wait for the kernel thread to acknowledge the suspend request and suspend itself.

The Fn 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 Fn kthread_suspend .

RETURN VALUES

The Fn kthread_create , Fn kthread_resume , and Fn kthread_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 Fn kproc_start , Fn kproc_shutdown , and Fn kthread_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 (;;) {
                 kthread_suspend_check(bufdaemonproc);
                 ...
         }
 }
 

ERRORS

The Fn kthread_resume and Fn kthread_suspend functions will fail if:

Bq Er EINVAL

The Fa p argument does not reference a kernel thread.

The Fn kthread_create function will fail if:

Bq Er 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

Bq Er EINVAL

The RFCFDG flag was specified in the Fa flags parameter.

SEE ALSO

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

HISTORY

The Fn kproc_start function first appeared in Fx 2.2 . The Fn kproc_shutdown , Fn kthread_create , Fn kthread_exit , Fn kthread_resume , Fn kthread_suspend , and Fn kthread_suspend_check functions were introduced in Fx 4.0 . Prior to Fx 5.0 , the Fn kproc_shutdown , Fn kthread_resume , Fn kthread_suspend , and Fn kthread_suspend_check functions were named Fn shutdown_kproc , Fn resume_kproc , Fn shutdown_kproc , and Fn kproc_suspend_loop , respectively.