NAME

fork1 — create a new process

SYNOPSIS

#include <sys/types.h>
#include <sys/proc.h>

int
fork1(struct proc *p1, int flags, void (*func)(void *), void *arg, register_t *retval, struct proc **rnewprocp);

DESCRIPTION

fork1() creates a new process out of p1, which should be the current thread. This function is used primarily to implement the fork(2) and vfork(2) system calls, as well as the kthread_create(9) function.

The flags argument is used to control the behavior of the fork and is created by a bitwise-OR of the following values:

FORK_FORK

The call is done by the fork(2) system call. Used only for statistics.

FORK_VFORK

The call is done by the vfork(2) system call. Used only for statistics.

FORK_PPWAIT

Suspend the parent process until the child is terminated (by calling _exit(2) or abnormally), or makes a call to execve(2).

FORK_SHAREFILES

Let the child share the file descriptor table with the parent through fdshare(). The default behavior is to copy the table through fdcopy().

FORK_IDLE

The new thread will be left in the SIDL state. The default behavior is to make it runnable and add it to the run queue.

FORK_NOZOMBIE

The child will be dissociated from the parent and will not leave a status for the parent to collect. See wait(2).

FORK_SHAREVM

The child will share the parent's address space. The default behavior is that the child gets a copy-on-write copy of the address space.

FORK_SYSTEM

The child will be marked as a system process.

FORK_PTRACE

The child will start with tracing enabled, as if ptrace(PT_TRACE_ME, 0, 0, 0) had been invoked in the child.

The new thread will begin execution by calling func, which must not be NULL. If arg is not NULL, it is passed as the argument to func. Otherwise, a pointer to the new process's only thread is passed.

If retval is not NULL, the PID of the child process will be stored in *retval on successful completion.

If rnewprocp is not NULL, the newly created thread is stored in *rnewprocp on successful completion.

RETURN VALUES

Upon successful completion of the fork operation, fork1() returns 0. Otherwise, the following error values are returned:

[EAGAIN]

The system limits on the total number of threads or processes would be exceeded.

[EAGAIN]

The limit RLIMIT_NPROC on the total number of processes under execution by this user id would be exceeded.

[ENOMEM]

There is insufficient swap space for the new thread.

SEE ALSO

execve(2), fork(2), vfork(2), kthread_create(9), psignal(9), tfind(9)

CAVEATS

The fork1 function semantics are specific to OpenBSD. Other BSD systems have different semantics.