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KTHREAD(9) | Kernel Developer's Manual | KTHREAD(9) |
NAME¶
kthread_start, kthread_shutdown, kthread_add, kthread_exit, kthread_resume, kthread_suspend, kthread_suspend_check — kernel threadsSYNOPSIS¶
#include <sys/kthread.h> voidkthread_start(const void *udata); void
kthread_shutdown(void *arg, int howto); void
kthread_exit(void); int
kthread_resume(struct thread *td); int
kthread_suspend(struct thread *td, int timo); void
kthread_suspend_check(struct thread *td); #include <sys/unistd.h> int
kthread_add(void (*func)(void *), void *arg, struct proc *procp, struct thread **newtdpp, int flags, int pages, const char *fmt, ...); 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 older family of kthread_*(9) functions was renamed to be the kproc_*(9) family of functions, as they were previously misnamed and actually produced kernel processes. This new family of kthread_*(9) functions was added to produce real kernel threads. See the kproc(9) man page for more information on the renamed calls. Also note that the kproc_kthread_add(9) function appears in both pages as its functionality is split. The function kthread_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 kthread_desc which describes the kernel thread that should be created:struct kthread_desc { char *arg0; void (*func)(void); struct thread **global_threadpp; };
- arg0
- String to be used for the name of the thread. This string will be copied into the td_name member of the new threads' struct thread.
- func
- The main function for this kernel thread to run.
- global_threadpp
- A pointer to a struct thread pointer
that should be updated to point to the newly created thread's
thread structure. If this variable is
NULL
, then it is ignored. The thread will be a subthread of proc0 (PID 0).
NULL
, to proc0. 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 thread. The newtdpp pointer points
to a struct thread pointer that is to be updated to
point to the newly created thread. If this argument is
NULL
, then it is ignored. The
flags argument may be set to
RFSTOPPED
to leave the thread in a stopped state. The
caller must call sched_add() to start the thread. 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 td_name member of the new thread's
struct thread.
The kproc_kthread_add() function is much like the
kthread_add() function above except that if the kproc does
not already exist, it is created. This function is better documented in the
kproc(9) manual page.
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 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
curthread 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 td argument points to the
struct thread 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 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
kthread_suspend().
RETURN VALUES¶
The kthread_add(), kthread_resume(), and kthread_suspend() functions return zero on success and non-zero on failure.EXAMPLES¶
This example demonstrates the use of a struct kthread_desc and the functions kthread_start(), kthread_shutdown(), and kthread_suspend_check() to run the bufdaemon process.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(bufdaemonthread); ... } }
ERRORS¶
The kthread_resume() and kthread_suspend() functions will fail if:- [
EINVAL
] - The td argument does not reference a kernel thread.
- [
ENOMEM
] - Memory for a thread's stack could not be allocated.
SEE ALSO¶
kproc(9), SYSINIT(9), wakeup(9)HISTORY¶
The kthread_start() function first appeared in FreeBSD 2.2 where it created a whole process. It was converted to create threads in FreeBSD 8.0. The kthread_shutdown(), kthread_exit(), kthread_resume(), kthread_suspend(), and kthread_suspend_check() functions were introduced in FreeBSD 4.0 and were converted to threads in FreeBSD 8.0. The kthread_create() call was renamed to kthread_add() in FreeBSD 8.0. The old functionality of creating a kernel process was renamed to kproc_create(9). Prior to FreeBSD 5.0, the kthread_shutdown(), kthread_resume(), kthread_suspend(), and kthread_suspend_check() functions were named shutdown_kproc(), resume_kproc(), shutdown_kproc(), and kproc_suspend_loop(), respectively.January 26, 2009 | Debian |