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.Dd $Mdocdate: December 29 2022 $
.Dt FORK1 9
.Os
.Sh NAME
.Nm fork1
.Nd create a new process
.Sh SYNOPSIS
.In sys/types.h
.In sys/proc.h
.Ft int
.Fo fork1
.Fa "struct proc *p1"
.Fa "int flags"
.Fa "void (*func)(void *)"
.Fa "void *arg"
.Fa "register_t *retval"
.Fa "struct proc **rnewprocp"
.Fc
.Sh DESCRIPTION
.Fn fork1
creates a new process out of
.Ar p1 ,
which should be the current thread.
This function is used primarily to implement the
.Xr fork 2
and
.Xr vfork 2
system calls, as well as the
.Xr kthread_create 9
function.
.Pp
The
.Ar flags
argument is used to control the behavior of the fork and is created by
a bitwise-OR of the following values:
.Bl -tag -width FORK_SHAREFILES
.It Dv FORK_FORK
The call is done by the
.Xr fork 2
system call.
Used only for statistics.
.It Dv FORK_VFORK
The call is done by the
.Xr vfork 2
system call.
Used only for statistics.
.It Dv FORK_PPWAIT
Suspend the parent process until the child is terminated (by calling
.Xr _exit 2
or abnormally), or makes a call to
.Xr execve 2 .
.It Dv FORK_SHAREFILES
Let the child share the file descriptor table with the parent through
.Fn fdshare .
The default behavior is to copy the table through
.Fn fdcopy .
.It Dv FORK_IDLE
The new thread will be left in the
.Dv SIDL
state.
The default behavior is to make it runnable and add it to the run queue.
.It Dv FORK_NOZOMBIE
The child will be dissociated from the parent and will not leave a status
for the parent to collect.
See
.Xr wait 2 .
.It Dv 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.
.It Dv FORK_SYSTEM
The child will be marked as a system process.
.It Dv FORK_PTRACE
The child will start with tracing enabled, as if
ptrace(PT_TRACE_ME, 0, 0, 0) had been invoked in the child.
.El
.Pp
The new thread will begin execution by calling
.Fa func ,
which must not be
.Dv NULL .
If
.Fa arg
is not
.Dv NULL ,
it is passed as the argument to
.Fa func .
Otherwise, a pointer to the new process's only thread is passed.
.Pp
If
.Fa retval
is not
.Dv NULL ,
the PID of the child process will be stored in
.Fa *retval
on successful completion.
.Pp
If
.Fa rnewprocp
is not
.Dv NULL ,
the newly created thread is stored in
.Fa *rnewprocp
on successful completion.
.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 system limits on the total number of threads or 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.
.It Bq Er ENOMEM
There is insufficient swap space for the new thread.
.El
.Sh SEE ALSO
.Xr execve 2 ,
.Xr fork 2 ,
.Xr vfork 2 ,
.Xr kthread_create 9 ,
.Xr psignal 9 ,
.Xr tfind 9
.Sh CAVEATS
The
.Nm
function semantics are specific to
.Ox .
Other
.Bx
systems have different semantics.