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$FreeBSD: releng/10.2/share/man/man9/kthread.9 269935 2014-08-13 12:41:31Z gavin $
.Dd July 15, 2014 .Dt KTHREAD 9 .Os .Sh NAME .Nm kthread_start , .Nm kthread_shutdown , .Nm kthread_add , .Nm kthread_exit , .Nm kthread_resume , .Nm kthread_suspend , .Nm kthread_suspend_check .Nd "kernel threads" .Sh SYNOPSIS n sys/kthread.h .Ft void .Fn kthread_start "const void *udata" .Ft void .Fn kthread_shutdown "void *arg" "int howto" .Ft void .Fn kthread_exit "void" .Ft int .Fn kthread_resume "struct thread *td" .Ft int .Fn kthread_suspend "struct thread *td" "int timo" .Ft void .Fn kthread_suspend_check "void" n sys/unistd.h .Ft int .Fo kthread_add .Fa "void (*func)(void *)" "void *arg" "struct proc *procp" .Fa "struct thread **newtdpp" "int flags" "int pages" .Fa "const char *fmt" ... .Fc .Ft int .Fo kproc_kthread_add .Fa "void (*func)(void *)" "void *arg" .Fa "struct proc **procptr" "struct thread **tdptr" .Fa "int flags" "int pages" "char * procname" "const char *fmt" "..." .Fc .Sh DESCRIPTION In .Fx 8.0 , the older family of .Fn kthread_* 9 functions was renamed to be the .Fn kproc_* 9 family of functions, as they were previously misnamed and actually produced kernel processes. This new family of .Fn kthread_* 9 functions was added to produce .Em real kernel threads. See the .Xr kproc 9 man page for more information on the renamed calls. Also note that the .Fn kproc_kthread_add 9 function appears in both pages as its functionality is split.
p The function .Fn kthread_start is used to start .Dq internal daemons such as .Nm bufdaemon , pagedaemon , vmdaemon , and the .Nm syncer and is intended to be called from .Xr SYSINIT 9 . The .Fa udata argument is actually a pointer to a .Vt "struct kthread_desc" which describes the kernel thread that should be created: d -literal -offset indent struct kthread_desc { char *arg0; void (*func)(void); struct thread **global_threadpp; }; .Ed
p The structure members are used by .Fn kthread_start as follows: l -tag -width ".Va global_threadpp" -offset indent t Va arg0 String to be used for the name of the thread. This string will be copied into the .Va td_name member of the new threads' .Vt "struct thread" . t Va func The main function for this kernel thread to run. t Va global_threadpp A pointer to a .Vt "struct thread" pointer that should be updated to point to the newly created thread's .Vt thread structure. If this variable is .Dv NULL , then it is ignored. The thread will be a subthread of .Va proc0 (PID 0). .El
p The .Fn kthread_add function is used to create a kernel thread. The new thread runs in kernel mode only. It is added to the process specified by the .Fa procp argument, or if that is .Dv NULL , to .Va proc0 . 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 thread. The .Fa newtdpp pointer points to a .Vt "struct thread" pointer that is to be updated to point to the newly created thread. If this argument is .Dv NULL , then it is ignored. The .Fa flags argument may be set to .Dv RFSTOPPED to leave the thread in a stopped state. The caller must call .Fn sched_add to start the thread. 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 .Xr printf 9 argument list that is used to build the name of the new thread and is stored in the .Va td_name member of the new thread's .Vt "struct thread" .
p The .Fn kproc_kthread_add function is much like the .Fn kthread_add function above except that if the kproc does not already exist, it is created. This function is better documented in the .Xr kproc 9 manual page.
p
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.
XXX "int ecode" argument isn't documented.
p 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 in order to check if the it has been asked to suspend. If it has, it will .Xr msleep 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 td argument points to the .Vt "struct thread" 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.
p The .Fn kthread_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 . .Sh RETURN VALUES The .Fn kthread_add , .Fn kthread_resume , and .Fn kthread_suspend functions return zero on success and non-zero on failure. .Sh EXAMPLES This example demonstrates the use of a .Vt "struct kthread_desc" and the functions .Fn kthread_start , .Fn kthread_shutdown , and .Fn kthread_suspend_check to run the .Nm bufdaemon process. d -literal -offset indent static struct thread *bufdaemonthread; static struct kthread_desc buf_kp = { "bufdaemon", buf_daemon, &bufdaemonthread }; SYSINIT(bufdaemon, SI_SUB_KTHREAD_BUF, SI_ORDER_FIRST, kthread_start, &buf_kp) static void buf_daemon() { ... /* * This process needs to be suspended prior to shutdown sync. */ EVENTHANDLER_REGISTER(shutdown_pre_sync, kthread_shutdown, bufdaemonthread, SHUTDOWN_PRI_LAST); ... for (;;) { kthread_suspend_check(); ... } } .Ed .Sh ERRORS The .Fn kthread_resume and .Fn kthread_suspend functions will fail if: l -tag -width Er t Bq Er EINVAL The .Fa td argument does not reference a kernel thread. .El
p The .Fn kthread_add function will fail if: l -tag -width Er t Bq Er ENOMEM Memory for a thread's stack could not be allocated. .El .Sh SEE ALSO .Xr kproc 9 , .Xr SYSINIT 9 , .Xr wakeup 9 .Sh HISTORY The .Fn kthread_start function first appeared in .Fx 2.2 where it created a whole process. It was converted to create threads in .Fx 8.0 . The .Fn kthread_shutdown , .Fn kthread_exit , .Fn kthread_resume , .Fn kthread_suspend , and .Fn kthread_suspend_check functions were introduced in .Fx 4.0 and were converted to threads in .Fx 8.0 . The .Fn kthread_create call was renamed to .Fn kthread_add in .Fx 8.0 . The old functionality of creating a kernel process was renamed to .Xr kproc_create 9 . Prior to .Fx 5.0 , the .Fn kthread_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.