NAME¶
kproc_start
,
kproc_shutdown
,
kproc_create
,
kproc_exit
,
kproc_resume
,
kproc_suspend
,
kproc_suspend_check
—
kernel processes
SYNOPSIS¶
#include
<sys/kthread.h>
void
kproc_start
(
const
void *udata);
void
kproc_shutdown
(
void
*arg,
int
howto);
int
kproc_create
(
void
(*func)(void *),
void *arg,
struct proc **newpp,
int flags,
int
pages,
const char *fmt,
...);
void
kproc_exit
(
int
ecode);
int
kproc_resume
(
struct
proc *p);
int
kproc_suspend
(
struct
proc *p,
int
timo);
void
kproc_suspend_check
(
struct
proc *p);
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
kthread*
(
9)
family of functions was renamed to be the
kproc*
(
9)
family of functions, as they were misnamed and actually produced kernel
processes. A new family of
different
kthread_*
(
9)
functions was added to produce
real kernel
threads. See the
kthread(9) man page for more information on those
calls. Also note that the
kproc_kthread_add
(
9)
function appears in both pages as its functionality is split.
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
process 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
kproc_create
() function is used to create
a kernel process. The new process shares its address space with process 0, the
swapper
process, and runs in kernel mode
only. The
func argument specifies the
function that the process 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 process'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 process and is stored in the
p_comm member of the new process's
struct proc.
The
kproc_exit
() function is used to
terminate kernel processes. It should be called by the main function of the
kernel process rather than letting the main function return to its caller. The
ecode argument specifies the exit status of
the process. While exiting, the function
exit1(9)
will initiate a call to
wakeup(9) on the process
handle.
The
kproc_resume
(),
kproc_suspend
(), and
kproc_suspend_check
() functions are used to
suspend and resume a kernel process. During the main loop of its execution, a
kernel process that wishes to allow itself to be suspended should call
kproc_suspend_check
() passing in
curproc as the only argument. This function
checks to see if the kernel process 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
process to continue. The other two functions are used to notify a kernel
process of a suspend or resume request. The
p
argument points to the
struct proc of the
kernel process to suspend or resume. For
kproc_suspend
(), the
timo argument specifies a timeout to wait for
the kernel process to acknowledge the suspend request and suspend itself.
The
kproc_shutdown
() function is meant to be
registered as a shutdown event for kernel processes that need to be suspended
voluntarily during system shutdown so as not to interfere with system shutdown
activities. The actual suspension of the kernel process is done with
kproc_suspend
().
The
kproc_kthread_add
() function is much like
the
kproc_create
() function above except
that if the kproc already exists, then only a new thread (see
kthread(9)) is created on the existing process.
The
func argument specifies the function that
the process 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
procptr pointer points to a
struct proc pointer that is the location to
be updated with the new proc pointer if a new process is created, or if not
NULL
, must contain the process pointer for
the already existing process. If this argument points to
NULL
, then a new process is created and the
field updated. If not NULL, the
tdptr pointer
points to a
struct thread pointer that is the
location to be updated with the new thread pointer. 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 procname argument is the name the new process should be given
if it needs to be created. It is
NOT a printf
style format specifier but a simple string. 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.
RETURN VALUES¶
The
kproc_create
(),
kproc_resume
(), and
kproc_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
kproc_start
(),
kproc_shutdown
(), and
kproc_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 (;;) {
kproc_suspend_check(bufdaemonproc);
...
}
}
ERRORS¶
The
kproc_resume
() and
kproc_suspend
() functions will fail if:
- [
EINVAL
]
- The p argument does not reference a
kernel process.
The
kproc_create
() function will fail if:
- [
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
.
- [
EINVAL
]
- The
RFCFDG
flag was specified in the
flags parameter.
SEE ALSO¶
rfork(2),
exit1(9),
kthread(9),
SYSINIT(9),
wakeup(9)
HISTORY¶
The
kproc_start
() function first appeared in
FreeBSD 2.2. The
kproc_shutdown
(),
kproc_create
(),
kproc_exit
(),
kproc_resume
(),
kproc_suspend
(), and
kproc_suspend_check
() functions were
introduced in
FreeBSD 4.0. Prior to
FreeBSD 5.0, the
kproc_shutdown
(),
kproc_resume
(),
kproc_suspend
(), and
kproc_suspend_check
() functions were named
shutdown_kproc
(),
resume_kproc
(),
shutdown_kproc
(), and
kproc_suspend_loop
(), respectively.
Originally they had the names
kthread_*
()
but were changed to
kproc_*
() when real
kthreads became available.