FORK1(9) | Kernel Developer's Manual | FORK1(9) |
fork1
—
#include <sys/types.h>
#include <sys/proc.h>
int
fork1
(struct
lwp *l1, int flags,
int exitsig,
void *stack,
size_t stacksize,
void (*func)(void *),
void *arg,
register_t *retval);
fork1
() creates a new process out of the process behind
l1, which is assumed to be the current lwp. This
function is used primarily to implement the
fork(2) and
vfork(2) system calls, but is
versatile enough to be used as a backend for e.g. the
__clone(2) call.
The flags argument controls the semantics of the fork operation, and is made up of the bitwise-OR of the following values:
A flags value of 0 indicates a standard fork operation.
The exitsig argument controls the signal sent to the parent on child death. If normal operation desired, SIGCHLD should be supplied.
It is possible to specify the child userspace stack location and
size by using the stack and
stacksize arguments, respectively. Values
NULL
and 0, respectively, will give the child the
default values for the machine architecture in question.
The arguments func and
arg can be used to specify a kernel function to be
called when the child process returns instead of
child_return
(). These are used for example in
starting the init process and creating kernel threads.
The retval argument is provided for the use of system call stubs. If retval is not NULL, it will hold the following values after successful completion of the fork operation:
User level system call stubs typically subtract 1 from retval[1] and bitwise-AND it with retval[0], thus returning the pid to the parent process and 0 to the child.
fork1
() returns 0. Otherwise, the following error
values are returned:
EAGAIN
]RLIMIT_NPROC
on the total number of
processes under execution by this user id would be exceeded.April 16, 2018 | NetBSD 9.0 |