NetBSD/share/man/man9/fork1.9

.\"	$NetBSD: fork1.9,v 1.5 2002/02/13 08:18:41 ross Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
.\" NASA Ames Research Center.
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.Dd January 6, 1998
.Dt FORK1 9
.Os
.Sh NAME
.Nm fork1
.Nd create a new process
.Sh SYNOPSIS
.Fd #include \*[Lt]sys/types.h\*[Gt]
.Fd #include \*[Lt]sys/proc.h\*[Gt]
.Ft int
.Fn "fork1" "struct proc *p1" "int flags" "register_t *retval" "struct proc **rnewprocp"
.Sh DESCRIPTION
.Fn fork1
creates a new process out of
.Ar p1 ,
which is assumed to be the current process.  This function is used primarily
to implement the
.Xr fork 2
and
.Xr vfork 2
system calls.
.Pp
The
.Ar flags
argument controls the semantics of the fork operation, and is made up of
the bitwise-OR of the following values:
.Bl -tag -width FORK_SHAREVM
.It FORK_PPWAIT
The parent process will sleep until the child process successfully calls
.Xr execve 2
or exits (either by a call to
.Xr _exit 2
or abnormally).
.It FORK_SHAREVM
The child process will share the parent's virtual address space.  If this
flag is not specified, the child will get a copy-on-write snapshot of the
parent's address space.
.El
.Pp
A
.Ar flags
value of 0 indicates a standard fork operation.
.Pp
The
.Ar retval
argument is provided for the use of system call stubs.  If
.Ar retval
is not NULL, it will hold the following values after successful completion
of the fork operation:
.Bl -tag -width retval[0]
.It Ar retval[0]
This will contain the pid of the child process.
.It Ar retval[1]
In the parent process, this will contain the value 0.  In the child process,
this will contain 1.
.El
.Pp
User level system call stubs typically subtract 1 from
.Ar retval[1]
and bitwise-AND it with
.Ar retval[0] ,
thus returning the pid to the parent process and 0 to the child.
.Pp
If
.Ar rnewprocp
is not NULL,
.Ar *rnewprocp
will point to the newly created process upon successful completion of
the fork operation.
.Sh RETURN VALUES
Upon successful completion of the fork operation,
.Fn fork1
returns 0.  Otherwise, the following error values are returned:
.Bl -tag -width [EAGAIN]
.It Bq Er EAGAIN
The limit on the total number of system processes would be exceeded.
.It Bq Er EAGAIN
The limit
.Dv RLIMIT_NPROC
on the total number of processes under execution by this
user id would be exceeded.
.El
.Sh SEE ALSO
.Xr execve 2 ,
.Xr fork 2 ,
.Xr vfork 2