166 lines
3.7 KiB
Text
166 lines
3.7 KiB
Text
.TH FORK 2
|
|
.SH NAME
|
|
fork, rfork \- manipulate process resources
|
|
.SH SYNOPSIS
|
|
.B #include <u.h>
|
|
.br
|
|
.B #include <libc.h>
|
|
.PP
|
|
.nf
|
|
.B
|
|
int fork(void)
|
|
.PP
|
|
.B
|
|
int rfork(int flags)
|
|
.fi
|
|
.SH DESCRIPTION
|
|
Forking is the only way new processes are created.
|
|
The
|
|
.I flags
|
|
argument to
|
|
.I rfork
|
|
selects which resources of the
|
|
invoking process (parent) are shared
|
|
by the new process (child) or initialized to
|
|
their default values.
|
|
The resources include
|
|
the file name space,
|
|
the open file descriptor table (which, when shared, permits processes
|
|
to open and close files for other processes),
|
|
the set of environment variables
|
|
(see
|
|
.IR env (3)),
|
|
the note group
|
|
(the set of processes that receive notes written to a member's
|
|
.B notepg
|
|
file;
|
|
see
|
|
.IR proc (3)),
|
|
the set of rendezvous tags
|
|
(see
|
|
.IR rendezvous (2));
|
|
and open files.
|
|
.I Flags
|
|
is the logical OR of some subset of
|
|
.TF RFCNAMEG
|
|
.TP
|
|
.B RFPROC
|
|
If set a new process is created; otherwise changes affect the
|
|
current process.
|
|
.TP
|
|
.B RFNOWAIT
|
|
If set, the child process will be dissociated from the parent. Upon
|
|
exit the child will leave no
|
|
.B Waitmsg
|
|
(see
|
|
.IR wait (2))
|
|
for the parent to collect.
|
|
.TP
|
|
.B RFNAMEG
|
|
If set, the new process inherits a copy of the parent's name space;
|
|
otherwise the new process shares the parent's name space.
|
|
Is mutually exclusive with
|
|
.BR RFCNAMEG .
|
|
.TP
|
|
.B RFCNAMEG
|
|
If set, the new process starts with a clean name space. A new
|
|
name space must be built from a mount of an open file descriptor.
|
|
Is mutually exclusive with
|
|
.BR RFNAMEG .
|
|
.TP
|
|
.B RFNOMNT
|
|
If set, subsequent mounts into the new name space and dereferencing
|
|
of pathnames starting with
|
|
.B #
|
|
are disallowed.
|
|
.TP
|
|
.B RFENVG
|
|
If set, the environment variables are copied;
|
|
otherwise the two processes share environment variables.
|
|
Is mutually exclusive with
|
|
.BR RFCENVG .
|
|
.TP
|
|
.B RFCENVG
|
|
If set, the new process starts with an empty environment.
|
|
Is mutually exclusive with
|
|
.BR RFENVG .
|
|
.TP
|
|
.B RFNOTEG
|
|
Each process is a member of a group of processes that all
|
|
receive notes when a note is written to any of their
|
|
.B notepg
|
|
files (see
|
|
.IR proc (3)).
|
|
The group of a new process is by default the same as its parent, but if
|
|
.B RFNOTEG
|
|
is set (regardless of
|
|
.BR RFPROC ),
|
|
the process becomes the first in a new group, isolated from
|
|
previous processes.
|
|
.TP
|
|
.B RFFDG
|
|
If set, the invoker's file descriptor table (see
|
|
.IR intro (2))
|
|
is copied; otherwise the two processes share a
|
|
single table.
|
|
.TP
|
|
.B RFCFDG
|
|
If set, the new process starts with a clean file descriptor table.
|
|
Is mutually exclusive with
|
|
.BR RFFDG .
|
|
.TP
|
|
.B RFREND
|
|
If set, the process will be unable to
|
|
.IR rendezvous (2)
|
|
with any of its ancestors; its children will, however, be able to
|
|
.B rendezvous
|
|
with it. In effect,
|
|
.B RFREND
|
|
makes the process the first in a group of processes that share a space for
|
|
.B rendezvous
|
|
tags.
|
|
.TP
|
|
.B RFMEM
|
|
If set, the child and the parent will share
|
|
.B data
|
|
and
|
|
.B bss
|
|
segments.
|
|
Otherwise, the child inherits a copy of those segments.
|
|
Other segment types, in particular stack segments, will be unaffected.
|
|
May be set only with
|
|
.BR RFPROC .
|
|
.PD
|
|
.PP
|
|
File descriptors in a shared file descriptor table are kept
|
|
open until either they are explicitly closed
|
|
or all processes sharing the table exit.
|
|
.PP
|
|
If
|
|
.B RFPROC
|
|
is set, the
|
|
value returned in the parent process
|
|
is the process id
|
|
of the child process; the value returned in the child is zero.
|
|
Without
|
|
.BR RFPROC ,
|
|
the return value is zero.
|
|
Process ids range from 1 to the maximum positive integer
|
|
.RB ( int )
|
|
value.
|
|
.I Rfork
|
|
may also return -1 if process resources are exhausted.
|
|
.PP
|
|
.I Fork
|
|
is just a call of
|
|
.BR rfork(RFFDG|RFREND|RFPROC) .
|
|
.SH SOURCE
|
|
.B /sys/src/libc/9syscall
|
|
.br
|
|
.B /sys/src/libc/9sys/fork.c
|
|
.SH SEE ALSO
|
|
.IR intro (2),
|
|
.IR proc (3),
|
|
.SH DIAGNOSTICS
|
|
These functions set
|
|
.IR errstr .
|