10564b1175
groff 1.23.0 added .MR to its -man macro package. The NEWS file states
that the inclusion of the macro "was prompted by its introduction to
Plan 9 from User Space's troff in August 2020." From d32deab it seems
that the name for Plan 9 from User Space's implementation was suggested
by groff maintainer G. Brandon Robinson.
Not sure if the intention was to make these definitions compatible, but
it would be nice if they were.
Currently, Plan 9 from User Space's .MR expects its second argument to
be parenthesized. groff's .MR does not. This results in extra
parentheses appearing in manual references when viewing Plan 9 from User
Space's manual pages on a system using groff.
164 lines
3.9 KiB
Groff
164 lines
3.9 KiB
Groff
.TH RFORK 3
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.SH NAME
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rfork \- manipulate process state
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.nf
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.B
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int rfork(int flags)
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.fi
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.SH DESCRIPTION
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.I Rfork
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is a partial implementation of the Plan 9 system call.
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It can be used to manipulate some process state and to create
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new processes a la
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.MR fork 2 .
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It cannot be used to create shared-memory processes
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(Plan 9's
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.B RFMEM
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flag); for that functionality use
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.I proccreate
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(see
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.MR thread 3 ).
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.PP
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The
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.I flags
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argument to
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.I rfork
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selects which resources of the
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invoking process (parent) are shared
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by the new process (child) or initialized to
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their default values.
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.I Flags
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is the logical OR of some subset of
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.TF RFCNAMEG
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.TP
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.B RFPROC
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If set a new process is created; otherwise changes affect the
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current process.
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.TP
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.B RFNOWAIT
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If set, the child process will be dissociated from the parent. Upon
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exit the child will leave no
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.B Waitmsg
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(see
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.MR wait 3 )
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for the parent to collect.
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.\" .TP
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.\" .B RFNAMEG
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.\" If set, the new process inherits a copy of the parent's name space;
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.\" otherwise the new process shares the parent's name space.
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.\" Is mutually exclusive with
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.\" .BR RFCNAMEG .
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.\" .TP
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.\" .B RFCNAMEG
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.\" If set, the new process starts with a clean name space. A new
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.\" name space must be built from a mount of an open file descriptor.
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.\" Is mutually exclusive with
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.\" .BR RFNAMEG .
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.\" .TP
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.\" .B RFNOMNT
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.\" If set, subsequent mounts into the new name space and dereferencing
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.\" of pathnames starting with
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.\" .B #
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.\" are disallowed.
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.\" .TP
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.\" .B RFENVG
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.\" If set, the environment variables are copied;
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.\" otherwise the two processes share environment variables.
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.\" Is mutually exclusive with
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.\" .BR RFCENVG .
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.\" .TP
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.\" .B RFCENVG
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.\" If set, the new process starts with an empty environment.
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.\" Is mutually exclusive with
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.\" .BR RFENVG .
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.TP
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.B RFNOTEG
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Each process is a member of a group of processes that all
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receive notes when a note is sent to the group
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(see
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.MR postnote 3
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and
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.MR signal 2 ).
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The group of a new process is by default the same as its parent, but if
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.B RFNOTEG
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is set (regardless of
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.BR RFPROC ),
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the process becomes the first in a new group, isolated from
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previous processes.
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In Plan 9, a process can call
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.B rfork(RFNOTEG)
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and then be sure that it will no longer receive console interrupts
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or other notes.
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Unix job-control shells put each command in its own process group
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and then relay notes to the current foreground command, making
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the idiom less useful.
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.TP
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.B RFFDG
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If set, the invoker's file descriptor table (see
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.IR intro ( ))
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is copied; otherwise the two processes share a
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single table.
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.\" .TP
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.\" .B RFCFDG
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.\" If set, the new process starts with a clean file descriptor table.
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.\" Is mutually exclusive with
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.\" .BR RFFDG .
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.\" .TP
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.\" .B RFREND
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.\" If set, the process will be unable to
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.\" .IR rendezvous (3)
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.\" with any of its ancestors; its children will, however, be able to
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.\" .B rendezvous
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.\" with it. In effect,
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.\" .B RFREND
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.\" makes the process the first in a group of processes that share a space for
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.\" .B rendezvous
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.\" tags.
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.\" .TP
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.\" .B RFMEM
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.\" If set, the child and the parent will share
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.\" .B data
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.\" and
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.\" .B bss
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.\" segments.
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.\" Otherwise, the child inherits a copy of those segments.
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.\" Other segment types, in particular stack segments, will be unaffected.
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.\" May be set only with
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.\" .BR RFPROC .
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.PD
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.PP
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File descriptors in a shared file descriptor table are kept
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open until either they are explicitly closed
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or all processes sharing the table exit.
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.PP
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If
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.B RFPROC
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is set, the
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value returned in the parent process
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is the process id
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of the child process; the value returned in the child is zero.
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Without
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.BR RFPROC ,
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the return value is zero.
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Process ids range from 1 to the maximum integer
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.RB ( int )
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value.
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.I Rfork
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will sleep, if necessary, until required process resources are available.
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.PP
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Calling
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.B rfork(RFFDG|RFPROC)
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is equivalent to calling
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.MR fork 2 .
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.SH SOURCE
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.B \*9/src/lib9/rfork.c
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.SH DIAGNOSTICS
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.I Rfork
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sets
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.IR errstr .
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