Provided by:
freebsd-manpages_6.2-1_all 
NAME
kproc_start, kproc_shutdown, kthread_create, kthread_exit,
kthread_resume, kthread_suspend, kthread_suspend_check - kernel threads
SYNOPSIS
#include <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);
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 thread that should be cre‐
ated:
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’ pro‐
cess 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 spec‐
ifies 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 execu‐
tion 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.
EXAMPLES
This example demonstrates the use of a struct kproc_desc and the func‐
tions kproc_start(), kproc_shutdown(), and 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 kthread_resume() and kthread_suspend() functions will fail if:
[EINVAL] The p argument does not reference a kernel thread.
The kthread_create() function will fail if:
[EAGAIN] The system-imposed limit on the total number of pro‐
cesses under execution would be exceeded. The limit
is given by the sysctl(3) MIB variable KERN_MAXPROC.
[EINVAL] The RFCFDG flag was specified in the flags parameter.
rfork(2), exit1(9), SYSINIT(9), wakeup(9)
HISTORY
The kproc_start() function first appeared in FreeBSD 2.2. The
kproc_shutdown(), kthread_create(), kthread_exit(), kthread_resume(),
kthread_suspend(), and kthread_suspend_check() functions were introduced
in FreeBSD 4.0. Prior to FreeBSD 5.0, the kproc_shutdown(),
kthread_resume(), kthread_suspend(), and kthread_suspend_check() func‐
tions were named shutdown_kproc(), resume_kproc(), shutdown_kproc(), and
kproc_suspend_loop(), respectively.