Simplify, do not install examples or info manual, and change license3.1.7

Signed-off-by: Mattias Andrée <maandree@kth.se>

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-\input texinfo   @c -*-texinfo-*-
-
-@c %**start of header
-@setfilename bus.info
-@settitle bus
-@afourpaper
-@documentencoding UTF-8
-@documentlanguage en
-@finalout
-@c %**end of header
-
-
-@dircategory Interprorcess Communication
-@direntry
-* bus: (bus).                        A simple daemonless system for broadcasting messages locally
-@end direntry
-
-
-@copying
-Copyright @copyright{} 2015 Mattias Andrée
-
-@quotation
-Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.3 or
-any later version published by the Free Software Foundation; with no
-Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
-Texts. A copy of the license is included in the section entitled
-``GNU Free Documentation License''.
-@end quotation
-@end copying
-
-@ifnottex
-@node Top
-@top bus -- A simple daemonless system for broadcasting messages locally
-@insertcopying
-@end ifnottex
-
-@titlepage
-@title bus
-@subtitle A simple daemonless system for broadcasting messages locally
-@author by Mattias Andrée (maandree)
-
-@page
-@vskip 0pt plus 1filll
-@insertcopying
-@page
-@end titlepage
-
-@contents
-
-
-@iftex
-@macro xrm{}
-@rm{}
-@end macro
-@macro xtt{}
-@tt{}
-@end macro
-@end iftex
-
-@ifnottex
-@macro xrm{}
-@end macro
-@macro xtt{}
-@end macro
-@end ifnottex
-
-@menu
-* Overview::                        Brief overview of @command{bus}.
-* Standard::                        How to use @command{bus} properly.
-* Invoking::                        Executing @command{bus}.
-* Interface::                       Using @command{libbus}.
-* Protocol::                        How communication over @command{bus} works internally.
-* Rationale::                       Why @command{bus}?
-* Examples::                        Usecase examples and API-demonstration.
-* GNU Free Documentation License::  Copying and sharing this manual.
-
-@detailmenu
- --- The Detailed Node Listing ---
-
-Invoking
-
-* bus create::                      Create a bus.
-* bus remove::                      Remove a bus.
-* bus listen::                      Listen for new message on a bus.
-* bus wait::                        Listen for one new message only on a bus.
-* bus broadcast::                   Broadcast a message on a bus.
-* bus chmod::                       Change permissions on a bus.
-* bus chown::                       Change ownership of a bus.
-* bus chgrp::                       Change group ownership of a bus.
-
-Examples
-
-* Audio-volume control::
-* Telephony and music::
-* Timed::
-* Nonblocking::
-* Daemon-dependencies::
-
-@end detailmenu
-@end menu
-
-
-
-@node Overview
-@chapter Overview
-
-@command{bus} is a stupid-simple, thrilless, daemonless interprocess
-communication system for broadcasting messages. It is a lightweight
-alternative to a two-phase interprocess flexible barrier.
-
-@command{bus} uses a System V semaphore array and System V shared
-memory. Buses are named; the key of the semaphore array and the
-shared memory is stored in a regular file.
-
-The shared memory used by @command{bus} is always 2048 bytes.
-Additionally all messages should be encoded in UTF-8 and not contain
-any NULL characters, except they @emph{must} always end with a NULL
-byte. Furthermore messages should be prefixed with the process
-identifer of the process whence the message originated, followed
-by a space. If the process is ephemeral@footnote{The process exits
-after the broadcast, or shortly thereafter.}, 0 should be used
-instead of the process identifier.
-
-Communication over @command{bus} is synchronous. The broadcast call
-does not return until all listeners have received (and copied) the
-message. A malfunctioning program can lock the bus.
-
-This software package contains a C library and a command line
-utility. The package python-bus provides a Python 3 module.
-
-
-
-@node Standard
-@chapter Standard
-
-The command @command{bus create} can be used to create new buses. By
-convention, buses should be stored in @file{$XDG_RUNTIME_DIR/bus},
-this is what @command{bus create} does if no pathname is given. The
-pathname of the bus should be tracked using @env{BUS_X}, where @env{X}
-is replaced with either:
-
-@table @env
-@item GENERIC
-For the bus used in generic cases. That is all but the cases
-of the buses listed below.
-@item AUDIO
-For the bus used in with the audio subsystem is involved.
-@item VIDEO
-For the bus used in with the video subsystem is involved.
-@item INPUT
-For the bus used in with the input subsystem is involved.
-@item FILES
-For the bus used in with the storage subsystem is involved.
-@end table
-
-This list may be extended in the future. Therefore, and for
-other conventions, project-private buses should be tracked
-using @env{X_BUS}, where @env{X} is the project name.
-
-Messages broadcasted on a bus cannot be longer than 2047 bytes,
-excluding NUL termination. Message should be encoded in UTF-8,
-and most not contain the NUL character.
-
-Broadcasted message should start with the process ID whence
-the message originated, followed by a single regular space.
-If the process is ephemeral@footnote{The process exits after
-the broadcast, or shortly thereafter.}, 0 should be used instead
-of the process identifier.
-
-
-
-@node Invoking
-@chapter Invoking
-
-@command{bus} includes the following commands:
-
-@table @command
-@item create
-Create a bus.
-See @ref{bus create} for more information.
-@item remove
-Remove a bus.
-See @ref{bus remove} for more information.
-@item listen
-Listen for new message on a bus.
-See @ref{bus listen} for more information.
-@item wait
-Listen for one new message only on a bus.
-See @ref{bus wait} for more information.
-@item broadcast
-Broadcast a message on a bus.
-See @ref{bus broadcast} for more information.
-@item chmod
-Change permissions on a bus.
-See @ref{bus chmod} for more information.
-@item chown
-Change ownership of a bus.
-See @ref{bus chown} for more information.
-@item chgrp
-Change group ownership of a bus.
-See @ref{bus chgrp} for more information.
-@end table
-
-Upon successful completion, these commands exit with the value
-0. On failure, they exit with the value 1. If the command is
-not recognised the exit value is 2.
-
-@menu
-* bus create::                      Create a bus.
-* bus remove::                      Remove a bus.
-* bus listen::                      Listen for new message on a bus.
-* bus wait::                        Listen for one new message only on a bus.
-* bus broadcast::                   Broadcast a message on a bus.
-* bus chmod::                       Change permissions on a bus.
-* bus chown::                       Change ownership of a bus.
-* bus chgrp::                       Change group ownership of a bus.
-@end menu
-
-
-
-@node bus create
-@section @command{bus create}
-
-The syntax for invocation of @command{bus create} is
-@example
-bus create [-x] [--] [@var{PATHNAME}]
-@end example
-
-The command creates a bus and stores the key to it in the
-file @var{PATHNAME}. If @var{PATHNAME} is omitted, a
-random pathname in @file{$XDG_RUNTIME_DIR/bus} will be
-used and printed to stdout.
-
-If @option{-x} is used, the command will fail if
-the file @var{PATHNAME} already exists.
-
-
-
-
-@node bus remove
-@section @command{bus remove}
-
-The syntax for invocation of @command{bus remove} is
-@example
-bus remove [--] @var{PATHNAME}
-@end example
-
-The command removes the bus whose key is stored in
-the file @var{PATHNAME}.  The file holding the
-key is also unlinked.
-
-
-
-@node bus listen
-@section @command{bus listen}
-
-The syntax for invocation of @command{bus command} is
-@example
-bus listen [--] @var{PATHNAME} @var{COMMAND}
-@end example
-
-The command listens for new messages on the bus whose
-key is stored in the file @var{PATHNAME}. Once a message
-is received, @var{COMMAND} will be spawned with the
-environment variable @env{msg} (lowercased) set to the
-received message. @sc{POSIX} shell syntax applies to
-@var{COMMAND}.
-
-
-@node bus wait
-@section @command{bus wait}
-
-The syntax for invocation of @command{bus wait} is
-@example
-bus wait [--] @var{PATHNAME} @var{COMMAND}
-@end example
-
-The command listens for a new message on the bus whose
-key is stored in the file @var{PATHNAME}. Once a message
-is received, the process will stop listening for more
-messages and @var{COMMAND} will be spawned with the
-environment variable @env{msg} (lowercased) set to the
-received message. @sc{POSIX} shell syntax applies to
-@var{COMMAND}.
-
-
-
-@node bus broadcast
-@section @command{bus broadcast}
-
-The syntax for invocation of @command{bus broadcast} is
-@example
-bus broadcast [-n] [--] @var{PATHNAME} @var{MESSAGE}
-@end example
-
-The command broadcasts the message @var{MESSAGE} on the
-bus whose key is stored in the file @var{PATHNAME}.
-
-
-
-@node bus chmod
-@section @command{bus chmod}
-
-The syntax for invocation of @command{bus chmod} is
-@example
-bus chmod [--] @var{PERMISSIONS} @var{PATHNAME}
-@end example
-
-This command changes who have access to the bus whose key
-is stored in the file @var{PATHNAME}. In the permissions,
-the owner, the group, and others (not in tgroup) are
-represented by the symbols @code{u}@footnote{@code{u}
-stands for `user'.}, @code{g}, and @code{o}, respectively.
-The permissions string is imagined to have always be
-prefixed with an @code{=}. This symbols means that all user
-classes list after it, and only those classes, as permission
-to use the bus. Similarly the symbols @code{+} and @code{-}
-can be used to grant and revoke access, respectively. The
-symbols @code{=}, @code{+}, and @code{-} can be mixed, and
-are interpreted from left to right. Alternatively the
-permissions string can be a octal number, where the  owner
-is represented by any bit in 700 (100, 200, or 400, or any
-combination thereof), the group is represented by any bit
-in 70, and others (not in the group) is represented by any
-bit in 7.
-
-The current permission of the bus can be retrieved by
-running @command{stat} over the file @var{PATHNAME}.
-
-
-
-@node bus chown
-@section @command{bus chown}
-
-The syntax for invocation of @command{bus chown} is
-@example
-bus chown [--] @var{OWNER}[:@var{GROUP}] @var{PATHNAME}
-@end example
-
-This command changes the owner, that owns the bus whose
-key is stored in the file @var{PATHNAME}, to the specified
-owner. The owner can be specified either with a numerical
-user identifier or with a user name. If a group is
-specified, the bus's owner-group will be set to that group,
-otherwise the group will remain unchanged (not changed
-to the group of the new owner.) The group can be specified
-either with a numerical group identifier or with a group
-name.
-
-The current ownership of the bus can be retrieved by
-running @command{stat} over the file @var{PATHNAME}.
-
-
-
-@node bus chgrp
-@section @command{bus chgrp}
-
-The syntax for invocation of @command{bus chgrp} is
-@example
-bus chgrp [--] @var{GROUP} @var{PATHNAME}
-@end example
-
-This command changes the group, that owns the bus whose
-key is stored in the file @var{PATHNAME}, to the specified
-group. The group can be specified either with a numerical
-group identifier or with a group name.
-
-The current ownership of the bus can be retrieved by
-running @command{stat} over the file @var{PATHNAME}.
-
-
-
-@node Interface
-@chapter Interface
-
-To use @command{libbus} in your C program, include the
-header file @file{<bus.h>} and link with the flag
-@option{-lbus}.
-
-With exception to @code{bus_poll} and @code{bus_poll_timed},
-all functions return @code{0} upon successful completion,
-and @code{-1} in case of failure. @code{bus_poll} and
-@code{bus_poll_timed} return @code{NULL} on failure.
-On failure on all functions set @code{errno} to indicate
-what went wrong.
-
-@file{<bus.h>} defines the following functions:
-
-@table @code
-@item int bus_create(const char *file, int flags, char **out_file)
-This function creates a bus with the asscoiated pathname
-specifed by the value of the parameter @code{file}. If
-@code{file} is @code{NULL} a random pathname is selected.
-This pathname adheres to the convention set forth by
-in @ref{Standard}.
-
-If @code{file} is not @code{NULL} the function fails if the
-file already exists if @code{flags} contains @code{BUS_EXCL}.
-Otherwise if @code{file} is not @code{NULL}, the function
-does nothing if the file already exists.
-
-If @code{flags} contains @code{BUS_INTR}, the function fails
-if it is interrupted.
-
-Unless @code{out_file} is NULL, the pathname of the bus
-should be stored in a new char array stored in @code{*out_file}.
-The caller must free the allocated stored in @code{*out_file}.
-
-If the processes cannot allocate enough memory to perform
-the action, the function sets @code{errno} to @code{ENOMEM}
-and fails. It may also fail and set @code{errno} to any of
-the errors specified for the system calls @code{open} and
-@code{write}.
-
-@item int bus_unlink(const char *file)
-This function removes the bus assoicated with the pathname
-stored in the parameter @code{file}. The function also
-unlinks the file.
-
-The function may set @code{errno} to any of the following
-values and fail for the specified reasons:
-@table @code
-@item EINVAL
-The bus does not exist.
-@item EACCES
-Operation permission is denied to the calling process.
-@item EPERM
-The user does not have permission to remove the bus.
-@end table
-@noindent
-It may also fail and set @code{errno} to any of the errors
-specified for the system calls @code{unlink} and @code{open},
-and the functions @code{semget} and @code{shmget}.
-
-@item int bus_open(bus_t *bus, const char *file, int flags)
-This function acquires resources required for the process
-to use the bus associated with the filename stored in the
-parameter @code{file}. The function also stores the resources
-in @code{bus} for use by other @command{bus} functions.
-
-Values for @code{flags} are constructed by a bitwise
-inclusive @sc{or} of flags from the following list.
-@table @code
-@item BUS_RDONLY
-The process will only be using the bus for receiving messages.
-@item BUS_WRONLY
-The process will only be using the bus for sending messages.
-@item BUS_RDWR
-The process will use the bus for both receiving and sending
-messages.
-@end table
-
-The function may set @code{errno} to any of the following
-values and fail for the specified reasons:
-@table @code
-@item ENOMEM
-The process cannot allocate enough memory to perform the
-action.
-@item EACCES
-Operation permission is denied to the calling process.
-@item EINVAL
-The described bus does not exist.
-@end table
-@noindent
-It may also fail and set @code{errno} to any of the errors
-specified for the system call @code{open}.
-
-@item int bus_close(bus_t *bus)
-This function disposes of resources allocated to the
-process, as referenced in the parameter @code{bus}.
-
-The function fails and sets @code{errno} to @code{EINVAL}
-if the bus does not exist.
-
-@item int bus_write(const bus_t *bus, const char *message, int flags)
-This function broadcasts a message on the bus whose
-information is stored in the parameter @code{bus}. The
-message read by the function is stored in the parameter
-@code{message}. It may not exceeed 2048 bytes, including
-NUL termination.
-
-The function shall fail, and set @code{errno} to
-@code{EAGAIN}, if the call would suspend the process and
-@code{flags} contains @code{BUS_NOWAIT}.
-
-The function may fail and set @code{errno} to any of the
-errors specified for the function @code{semop}.
-
-@item int bus_write_timed(const bus_t *bus, const char *message, const struct timespec *timeout, clockid_t clockid)
-This function behaves like @code{bus_write}, except if it
-is not able to write the message within the specified time,
-it will fail and set @code{errno} to @code{EAGAIN}. The
-time is specified as an absolute time using the parameter
-@code{timeout}. The behaviour is unspecified if @code{timeout}
-is @code{NULL}. @code{timeout} is measured with the clock whose
-identifier is specified by the parameter @code{clockid}. This
-clock must be a predicitable clock@footnote{There are probably
-other, undocumented, seemingly arbitrary restrictions too.}.
-
-The function may fail and set @code{errno} to any of the
-errors specified for the functions @code{semop} and
-@code{clock_gettime}.
-
-@item int bus_read(const bus_t *bus, int (*callback)(const char *message, void *user_data), void *user_data)
-This function waits for new message to be sent on the bus
-specified in the @code{bus} parameter, as provieded by a
-previous call to the function @code{bus_open}. Once a
-message is received, the parameter-function @code{callback}
-is invoked. The parameter @code{message} in @code{callback}
-is the received message, and @code{user_data} in
-@code{callback} should be @code{user_data} from @code{bus_read}.
-However, once the function [@code{bus_read}] has ensured
-that it will receive any message sent on the bus, it shall
-invoke the parameter-function @code{callback} with
-@code{message} set to @code{NULL}, to notify the process that
-it can perform any action that requires that it is listening
-on the bus.
-
-After @code{callback} returns, @code{message} may be override.
-Therefore @code{callback} should copy message and start a new
-thread that uses the copy of @code{message}. @code{callback}
-shall return @code{-1} on failure, @code{0} if the function
-[@code{bus_read}] should stop listening, or @code{1} if
-the function should continue listening.
-
-The function may fail and set @code{errno} to any of the
-errors specified for the function @code{semop}.
-
-@item int bus_read_timed(const bus_t *bus, int (*callback)(const char *message, void *user_data), void *user_data, const struct timespec *timeout, clockid_t clockid)
-This function behaves like @code{bus_read}, except it will
-automatically fail and set @code{errno} to @code{EAGAIN} when
-the specified time has passed. The time is specified as an
-absolute time using the parameter @code{timeout}. The
-behaviour is unspecified if @code{timeout} is @code{NULL}.
-@code{timeout} is measured with the clock whose identifier
-is specified by the parameter @code{clockid}. This clock
-must be a predicitable clock@footnote{There are probably
-other, undocumented, seemingly arbitrary restrictions too.}.
-
-The function may fail and set @code{errno} to any of the
-errors specified for the functions @code{semop} and
-@code{clock_gettime}.
-
-@item int bus_poll_start(bus_t *bus)
-@itemx int bus_poll_stop(const bus_t *bus)
-@itemx const char *bus_poll(bus_t *bus, int flags)
-@itemx const char *bus_poll_timed(bus_t *bus, const struct timespec *timeout, clockid_t clockid)
-The function @code{bus_poll} waits for a message to be
-broadcasted on the bus, and return the message it receives.
-The function fails if @code{flags} contains @code{BUS_NOWAIT}
-and there is not already a message waiting on the bus.
-Received messages shall be copied and parsed, and acted
-upon, in a separate thread, and the function @code{bus_poll}
-or the function @code{bus_poll_stop} called again as soon
-as possible.
-
-The funcion @code{bus_poll_start} must be called before
-@code{bus_poll} is called for the first time. When the
-process is done listening on the bus, it must call the
-function @code{bus_poll_stop}.
-
-The function @code{bus_poll_timed} behaves like the function
-@code{bus_poll}, except if it is not able to read a message
-within the specified time, it will fail and set @code{errno}
-to @code{EAGAIN}. The time is specified as an absolute time
-using the parameter @code{timeout}. The behaviour is
-unspecified if @code{timeout} is @code{NULL}. @code{timeout}
-is measured with the clock whose identifier is specified by
-the parameter @code{clockid}. This clock must be a predicitable
-clock@footnote{There are probably other, undocumented,
-seemingly arbitrary restrictions too.}.
-
-Upon successful completion, the functions @code{bus_poll} and
-@code{bus_poll_timed} returns the received message.
-
-These functions may fail and set @code{errno} to any of the
-errors specified for the function @code{semop}. The function
-@code{bus_poll_timed} may also set @code{errno} to any of
-the errors specified for @code{clock_gettime}.
-
-@item int bus_chown(const char *file, uid_t owner, gid_t group)
-This function changes the owner and the group of the bus,
-associated with the file whose pathname is stored in the
-parameter @code{file}, to the owner and group specified by
-the parameters @code{owner} and @code{group}, respectively.
-
-The current ownership of a bus can be retrieved by calling
-@code{stat} over the pathname of the bus.
-
-The function may fail and set @code{errno} to any of the
-errors specified for the functions @code{bus_open},
-@code{chown}, @code{semget}, @code{shmget}, and @code{shmctl}
-as well as any errors specified for the commands
-@code{IPC_STAT} and @code{IPC_SET} for the function
-@code{semctl}.
-
-@item int bus_chmod(const char *file, mode_t mode)
-This function gives access to the bus associated with the
-file whose pathname is stored in the parameter @code{file}
-according to the following rules:
-
-@itemize @bullet{}
-@item
-If @code{mode} contains any of the bits @code{S_IRWXU}
-contains, the owner should be given full access to the
-bus. Otherwise the owner should have no access.
-@item
-If @code{mode} contains any of the bits @code{S_IRWXG}
-contains, the group should be given read and write
-access to the bus. Otherwise the group should have no
-access.
-@item
-If @code{mode} contains any of the bits @code{S_IRWXO}
-contains, users that are neither the owner nor member
-of the group should be given read and write access to
-the bus. Otherwise they should have no access.
-@end itemize
-
-The current permissions of a bus can be retrieved by calling
-@code{stat} over the pathname of the bus.
-
-The function may fail and set @code{errno} to any of the
-errors specified for the functions @code{bus_open},
-@code{chmode}, @code{semget}, @code{shmget}, and @code{shmctl}
-as well as any errors specified for the commands
-@code{IPC_STAT} and @code{IPC_SET} for the function
-@code{semctl}.
-@end table
-
-There is not reason for poking around in @code{bus_t}
-(@code{struct bus}). It should be considered opaque.
-You can read the documentation in @file{<bus.h>} if
-you want to know what is in it.
-
-
-
-
-@node Protocol
-@chapter Protocol
-
-@command{bus} is built upon following three procedures.
-
-@noindent
-@code{create}
-@example
-@w{@xrm{}Select a filename.@xtt{}}
-
-@w{@xrm{}Create XSI semaphore array @{@code{S} = 0, @code{W} = 0, @code{X} = 1, @code{Q} = 0, @code{N} = 0@}@xtt{}}
-@w{@xrm{}with random key. Store the semaphore array's key in decimal form@xtt{}}
-@w{@xrm{}on the first line in the selected file.@xtt{}}
-
-@w{@xrm{}Create XSI shared memory, with an allocation of 2048 bytes, with@xtt{}}
-@w{@xrm{}a random key. Store the shared memory's key in decimal form on@xtt{}}
-@w{@xrm{}the second line in the selected file.@xtt{}}
-@end example
-
-@noindent
-@code{broadcast}
-@example
-with P(X):
-  Z(W)
-  @w{@xrm{}Write NUL-terminate message to shared memory@xtt{}}
-  with V(N): -- (1)
-    Q := 0
-    Z(S)
-
--- (1) @w{@xrm{}may be omitted if semaphores are known that@xtt{}}
-   @w{P()@xrm{}, @xtt{}Z()@xrm{}, @xtt{}V()@xrm{} cannot create a race condition@xtt{}}
-   @w{@xrm{}with a processes running @xtt{}Z()@xrm{}.@xtt{}}
-@end example
-
-@noindent
-@code{listen}
-@example
-with V(S):
-  forever:
-    V(Q)
-    Z(Q)
-    @w{@xrm{}Read NUL-terminated message from shared memory@xtt{}}
-    if breaking:
-      break
-    with V(W):
-      with P(S):
-        Z(S)
-        Z(N)
-@end example
-
-@noindent
-@code{V(a)} means that semaphore a is released.@*
-@code{P(a)} means that semaphore a is acquired.@*
-@code{Z(a)} means that the process waits for semaphore a to become 0.@*
-@code{with P(a)} that @code{P(a)} is done before the entering the scope,
-and @code{V(a)} is done when exiting the scope. It also means that
-these actions [@code{P(a)} and @code{V(a)}] are undone when the process
-exits, or if the call fails.@*
-@code{with V(a)} is to @code{V(a)} as @code{with P(a)} is to @code{P(a)}.
-
-
-
-@node Rationale
-@chapter Rationale
-
-We need an interprocess communication system similar
-to message queues. But we need broadcasting rather than
-anycasting, so we have a fast, simple and daemonless
-system for announcing events to any processes that
-might be interested.
-
-
-
-@node Examples
-@chapter Examples
-
-This chapter contains usecase examples and
-API-demonstrations. You will find that they are (on
-a standard installation) installed on your system.
-
-@menu
-* Audio-volume control::
-* Telephony and music::
-* Timed::
-* Nonblocking::
-* Daemon-dependencies::
-@end menu
-
-
-
-
-@node Audio-volume control
-@section Audio-volume control
-
-Assume you have program that display the audio volume.
-This program checks every second third if the volume
-have changed.
-
-Also assume that you use @command{amixer} to change the
-volume, most often by using keybindings via @command{xbindkeys}.
-
-To reduce the delay, you want to send a signal to the
-monitor program that the volume have changed. For this
-more primitive IPC is sufficient, but lets assume there
-are other programs interested in this information too.
-
-To accomplish this, you create a wrapper for @command{amixer}
-that broadcasts updates on a bus. This wrapper is
-installed as @command{~/.local/bin/amixer}, and
-@command{~/.local/bin/} is included in @env{$PATH}
-before @command{/usr/bin}.
-@*
-
-@noindent
-Before starting run @command{./init}, this code is
-should be run from your profile file if you want to
-implement this on your system. After running
-@command{./init}, you can start one or more listeners
-by running @command{./alsa-monitor}.
-
-To change the volume run
-@code{./amixer -c 0 -- set Master 5%+} or similar.
-
-When you are done run @command{./cleanup}.
-
-
-@subsubheading @file{./amixer}
-@example
-#!/bin/sh
-/usr/bin/amixer "$@@"
-for arg in "$@@"; do
-  if [ "$@{arg@}" = "set" ]  || \
-     [ "$@{arg@}" = "sset" ] || \
-     [ "$@{arg@}" = "cset" ]; then
-    exec bus broadcast "/tmp/example-bus" '0 volume-changed *'
-  fi
-done
-@end example
-
-
-@subsubheading @file{./cleanup}
-@example
-#!/bin/sh
-exec bus remove "/tmp/example-bus"
-@end example
-
-
-@subsubheading @file{./init}
-@example
-#!/bin/sh
-bus create "/tmp/example-bus"
-
-# @w{@xrm{}The following code is more suitable in the real world,@xtt{}}
-# @w{@xrm{}if used, the other files should use @xtt{}"$@{BUS_AUDIO@}"}
-# @w{@xrm{}instead of @xtt{}"/tmp/example-bus"@xrm{}.@xtt{}}
-# 
-# export BUS_AUDIO="$@{XDG_RUNTIME_DIR@}/bus/audio"
-# if [ ! -f "$@{BUS_AUDIO@}" ]; then
-#   bus create "$@{BUS_AUDIO@}"
-# fi
-@end example
-
-
-@subsubheading @file{./monitor}
-@example
-#!/bin/sh
-if [ $# = 1 ]; then
-  if [ "$(echo "$@{1@}" | cut -d ' ' -f 2)" = "volume-changed" ]; then
-    printf '\e[H\e[2J'
-    amixer get Master
-  fi
-  exit 0
-fi
-
-exec 2>/dev/null
-
-printf '\e[?1049h\e[H\e[2J'
-trap -- "printf '\e[?1049l'" SIGINT
-bus listen "/tmp/example-bus" \'"$@{0/\'/\'\\\'\'@}"\'' "$@{msg@}"'
-@end example
-
-
-
-@node Telephony and music
-@section Telephony and music
-
-Assume you have a music player and a telephony program.
-You might like it if the music player pauses whenever
-you make or receive a call. You may also like it, if
-the music resumed when the call ended.
-
-In this example we will assume you the have @command{mocp}
-(@command{moc} package) running. And we will use the shell to
-simulate a telephony program.
-@*
-
-@noindent
-First of, run make to build this example. Before
-starting run @command{./init}. And when you are
-done run @command{./cleanup}.
-
-In one terminal run @command{./monitor}. This program
-will pause @command{mocp} when you make or receive a call,
-it will also resume @command{mocp} when all calls have
-ended if it did pause @command{mocp}.
-
-Then start any positive number of terminals.
-We will pretend that each of them are telephony
-programs. To make or receive a call, run
-@command{./receive-or-make-call}, when you want to
-end the pretend call, run @command{./end-call} from
-the terminal (or more accurately, from the same
-process.)
-
-
-@subsubheading @file{./Makefile}
-@example
-COMMANDS = init cleanup monitor end-call receive-or-make-call
-
-all: $@{COMMANDS@}
-%: %.c
-        $@{CC@} -Wall -Wextra -pedantic -std=c99 -lbus -o $@@ $<
-clean:
-        -rm $@{COMMANDS@}
-
-.PHONY: all clean
-@end example
-
-
-@subsubheading @file{./cleanup.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-
-int main()
-@{
-  return bus_unlink("/tmp/example-bus") && (perror("cleanup"), 1);
-@}
-@end example
-
-
-@subsubheading @file{./end-call.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <stdint.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static char message[BUS_MEMORY_SIZE];
-
-int main()
-@{
-  bus_t bus;
-  sprintf(message, "%ji unforce-pause", (intmax_t)getppid());
-  /* @w{@xrm{}Yes, PPID; in this example we pretend the shell is the telephony process.@xtt{}} */
-  t (bus_open(&bus, "/tmp/example-bus", BUS_WRONLY));
-  t (bus_write(&bus, message, 0));
-  bus_close(&bus);
-  return 0;
-
-fail:
-  perror("end-call");
-  bus_close(&bus);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./init.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-
-int main()
-@{
-  return bus_create("/tmp/example-bus", 0, NULL) && (perror("init"), 1);
-@}
-@end example
-
-
-@subsubheading @file{./monitor.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-
-static size_t pauser_count = 0;
-static size_t pausers_size = 0;
-static char* pausers = NULL;
-
-static int is_moc_playing(void)
-@{
-  return !WEXITSTATUS(system("env LANG=C mocp -i 2>/dev/null |"
-                             "grep 'State: PLAY' >/dev/null"));
-@}
-
-/* @w{@xrm{}In a proper implementation, message whould be copyied, and then@xtt{}}
- * @w{@xrm{}a new thread would be created that parsed the copy. But that is@xtt{}}
- * @w{@xrm{}too much for an example, especially since it would also require@xtt{}}
- * @w{@xrm{}a mutex to make sure two threads do not modify data at the same@xtt{}}
- * @w{@xrm{}time, causing chaos.@xtt{}} */
-static int callback(const char *message, void *user_data)
-@{
-  char *msg = NULL;
-  size_t len = 0;
-  if (message == 0)
-    return 1;
-  while ((len < 2047) && message[len])
-    len++;
-  msg = malloc((len + 1) * sizeof(char));
-  t (msg == NULL);
-  memcpy(msg, message, len * sizeof(char));
-  msg[len] = 0;
-  /* @w{@xrm{}BEGIN run as in a separate thread@xtt{}} */
-  if (pauser_count || is_moc_playing()) @{
-    char *begin = strchr(msg, ' ');
-    ssize_t pid;
-    int requests_pause;
-    if (begin == NULL)
-      goto done;
-    *begin++ = 0;
-    pid = (ssize_t)atoll(msg);
-    if (pid < 1) /* @w{@xrm{}We need a real PID, too bad there is@xtt{}}
-                  * @w{@xrm{}no convient way to detect if it dies.@xtt{}} */
-      goto done;
-    if ((strstr(begin, "force-pause ") == begin) ||
-        !strcmp(begin, "force-pause"))
-      requests_pause = 1;
-    else if ((strstr(begin, "unforce-pause ") == begin) ||
-             !strcmp(begin, "unforce-pause"))
-      requests_pause = 0;
-    else
-      goto done;
-    if ((size_t)pid >= pausers_size) @{
-      pausers = realloc(pausers, (size_t)(pid + 1) * sizeof(char));
-      t (pausers == NULL); /* @w{@xrm{}Let's ignore the memory leak.@xtt{}} */
-      memset(pausers + pausers_size, 0,
-             ((size_t)(pid + 1) - pausers_size) * sizeof(char));
-      pausers_size = (size_t)(pid + 1);
-    @}
-    if (pausers[pid] ^ requests_pause) @{
-      pauser_count += requests_pause ? 1 : -1;
-      pausers[pid] = requests_pause;
-      if (pauser_count == (size_t)requests_pause)
-        system(requests_pause ? "mocp -P" : "mocp -U");
-    @}
-  @}
-  /* @w{@xrm{}END run as in a separate thread@xtt{}} */
-  goto done;
-  (void) user_data;
-
-fail:
-  perror("monitor");
-  return -1;
-
-done:
-  free(msg);
-  return 1;
-@}
-
-int main()
-@{
-  bus_t bus;
-  t (bus_open(&bus, "/tmp/example-bus", BUS_RDONLY));
-  t (bus_read(&bus, callback, NULL));
-  bus_close(&bus);
-  free(pausers);
-  return 0;
-
-fail:
-  perror("monitor");
-  bus_close(&bus);
-  free(pausers);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./receive-or-make-call.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <stdint.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static char message[BUS_MEMORY_SIZE];
-
-int main()
-@{
-  bus_t bus;
-  sprintf(message, "%ji force-pause", (intmax_t)getppid());
-  /* @w{@xrm{}Yes, PPID; in this example we pretend the shell is the telephony process.@xtt{}} */
-  t (bus_open(&bus, "/tmp/example-bus", BUS_WRONLY));
-  t (bus_write(&bus, message, 0));
-  bus_close(&bus);
-  return 0;
-
-fail:
-  perror("receive-or-make-call");
-  bus_close(&bus);
-  return 1;
-@}
-@end example
-
-
-
-@node Timed
-@section Timed
-
-This example shows how to use timed operations.
-
-First of, run make to build this example.
-
-To start the example run @command{./init}. When you are
-done run @command{./cleanup}.
-
-Running instances of @command{./poll} will wait for new
-messages continuously, but with one second timeouts.
-
-@command{./slow-poll} works like @command{./poll}, except
-it will sleep for one second every time it receives
-a message.
-
-Running instances of @command{./read} will read for ten
-seconds and then time out.
-
-@command{./poll}, @command{./read}, and @command{./slow-poll}
-will stop if the message "stop" is broadcasted.
-
-@command{./write} will wait for atmost a tenth of a
-seconds before failing. This means that if two instances
-of @command{./write} is started at the same time one of
-them will fail if @command{./slow-poll} is running.
-
-@command{./poll}, @command{./read}, @command{./init} and
-@command{./cleanup} are run without any additional
-arguments. @command{./write} is run with the message
-as the second argument.
-
-
-@subsubheading @file{./Makefile}
-@example
-COMMANDS = init cleanup write poll read slow-poll
-
-all: $@{COMMANDS@}
-%: %.c
-        $@{CC@} -Wall -Wextra -pedantic -std=c99 -lbus -o $@@ $<
-clean:
-        -rm $@{COMMANDS@}
-
-.PHONY: all clean
-@end example
-
-
-@subsubheading @file{./cleanup.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-
-int main()
-@{
-  return bus_unlink("/tmp/example-bus") && (perror("cleanup"), 1);
-@}
-@end example
-
-
-@subsubheading @file{./init.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-
-int main()
-@{
-  return bus_create("/tmp/example-bus", 0, NULL) && (perror("init"), 1);
-@}
-@end example
-
-
-@subsubheading @file{./poll.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <string.h>
-#include <errno.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-int main()
-@{
-  bus_t bus;
-  const char *message;
-  long long tick = 0;
-  struct timespec timeout;
-  t (bus_open(&bus, "/tmp/example-bus", BUS_RDONLY));
-  t (bus_poll_start(&bus));
-  for (;;) @{
-    t (clock_gettime(CLOCK_MONOTONIC, &timeout));
-    timeout.tv_sec += 1;
-    message = bus_poll_timed(&bus, &timeout, CLOCK_MONOTONIC);
-    if (message == NULL) @{
-      t (errno != EAGAIN);
-      printf("waiting... %lli\n", ++tick);
-      continue;
-    @}
-    tick = 0;
-    message = strchr(message, ' ') + 1;
-    if (!strcmp(message, "stop"))
-      break;
-    printf("\033[01m%s\033[21m\n", message);
-  @}
-  t (bus_poll_stop(&bus));
-  bus_close(&bus);
-  return 0;
-
-fail:
-  perror("poll");
-  bus_poll_stop(&bus);
-  bus_close(&bus);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./read.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <string.h>
-#include <errno.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static int callback(const char *message, void *user_data)
-@{
-  (void) user_data;
-
-  if (message == NULL)
-    return 1;
-
-  message = strchr(message, ' ') + 1;
-  if (!strcmp(message, "stop"))
-    return 0;
-  printf("%s\n", message);
-  return 1;
-@}
-
-int main()
-@{
-  bus_t bus;
-  struct timespec timeout;
-  t (bus_open(&bus, "/tmp/example-bus", BUS_RDONLY));
-  t (clock_gettime(CLOCK_MONOTONIC, &timeout));
-  timeout.tv_sec += 10;
-  t (bus_read_timed(&bus, callback, NULL, &timeout, CLOCK_MONOTONIC));
-  bus_close(&bus);
-  return 0;
-
-fail:
-  perror("poll");
-  bus_poll_stop(&bus);
-  bus_close(&bus);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./slow-poll.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <string.h>
-#include <errno.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-int main()
-@{
-  bus_t bus;
-  const char *message;
-  long long tick = 0;
-  struct timespec timeout;
-  t (bus_open(&bus, "/tmp/example-bus", BUS_RDONLY));
-  t (bus_poll_start(&bus));
-  for (;;) @{
-    t (clock_gettime(CLOCK_MONOTONIC, &timeout));
-    timeout.tv_sec += 1;
-    message = bus_poll_timed(&bus, &timeout, CLOCK_MONOTONIC);
-    if (message == NULL) @{
-      t (errno != EAGAIN);
-      printf("waiting... %lli\n", ++tick);
-      continue;
-    @}
-    tick = 0;
-    message = strchr(message, ' ') + 1;
-    if (!strcmp(message, "stop"))
-      break;
-    printf("\033[01m%s\033[21m\n", message);
-    sleep(1);
-  @}
-  t (bus_poll_stop(&bus));
-  bus_close(&bus);
-  return 0;
-
-fail:
-  perror("poll");
-  bus_poll_stop(&bus);
-  bus_close(&bus);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./write.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <stdint.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static char message[BUS_MEMORY_SIZE];
-
-int main(int argc, char *argv[])
-@{
-  bus_t bus;
-  struct timespec timeout;
-  if (argc < 2) @{
-    fprintf(stderr, "%s: USAGE: %s message\n", argv[0], argv[0]);
-    return 2;
-  @}
-  sprintf(message, "0 %s", argv[1]);
-  t (bus_open(&bus, "/tmp/example-bus", BUS_WRONLY));
-  t (clock_gettime(CLOCK_MONOTONIC, &timeout));
-  timeout.tv_nsec += 100000000L;
-  t (bus_write_timed(&bus, message, &timeout, CLOCK_MONOTONIC));
-  bus_close(&bus);
-  return 0;
-
-fail:
-  perror("write");
-  bus_close(&bus);
-  return 1;
-@}
-@end example
-
-
-
-@node Nonblocking
-@section Nonblocking
-
-This example shows how to use bus_poll instead of bus_read,
-and how to do non-blocking polling and non-blocking writing.
-
-First of, run make to build this example.
-
-To start the example run @command{./init}. When you are done
-run @command{./cleanup}.
-
-Running instances of @command{./poll} will check every second
-if there is a new inbound message. Between these checks
-@command{./write} will wait for all @command{./poll}:s to
-receive the message. This means that @command{./write} blocks
-while @command{./poll} sleeps. If two or more instances of
-@command{./write} is started at approximately the same time,
-only one will continue to write a message on the bus, the
-others will fail.
-
-@command{./poll} will stop if the message ``stop'' is
-broadcasted.
-
-@command{./poll}, @command{./init} and @command{./cleanup}
-are run without any additional arguments. @command{./write}
-is run with the message as the second argument.
-
-
-@subsubheading @file{./Makefile}
-@example
-COMMANDS = init cleanup write poll
-
-all: $@{COMMANDS@}
-%: %.c
-        $@{CC@} -Wall -Wextra -pedantic -std=c99 -lbus -o $@@ $<
-clean:
-        -rm $@{COMMANDS@}
-
-.PHONY: all clean
-@end example
-
-
-@subsubheading @file{./cleanup.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-
-int main()
-@{
-  return bus_unlink("/tmp/example-bus") && (perror("cleanup"), 1);
-@}
-@end example
-
-
-@subsubheading @file{./init.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-
-int main()
-@{
-  return bus_create("/tmp/example-bus", 0, NULL) && (perror("init"), 1);
-@}
-@end example
-
-
-@subsubheading @file{./poll.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <string.h>
-#include <errno.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-int main()
-@{
-  bus_t bus;
-  const char *message;
-  long long tick = 0;
-  t (bus_open(&bus, "/tmp/example-bus", BUS_RDONLY));
-  t (bus_poll_start(&bus));
-  for (;;) @{
-    message = bus_poll(&bus, BUS_NOWAIT);
-    if (message == NULL) @{
-      t (errno != EAGAIN);
-      printf("waiting... %lli\n", ++tick);
-      sleep(1);
-      continue;
-    @}
-    tick = 0;
-    message = strchr(message, ' ') + 1;
-    if (!strcmp(message, "stop"))
-      break;
-    printf("\033[01m%s\033[21m\n", message);
-  @}
-  t (bus_poll_stop(&bus));
-  bus_close(&bus);
-  return 0;
-
-fail:
-  perror("poll");
-  bus_poll_stop(&bus);
-  bus_close(&bus);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./write.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <stdint.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static char message[BUS_MEMORY_SIZE];
-
-int main(int argc, char *argv[])
-@{
-  bus_t bus;
-  if (argc < 2) @{
-    fprintf(stderr, "%s: USAGE: %s message\n", argv[0], argv[0]);
-    return 2;
-  @}
-  sprintf(message, "0 %s", argv[1]);
-  t (bus_open(&bus, "/tmp/example-bus", BUS_WRONLY));
-  t (bus_write(&bus, message, BUS_NOWAIT));
-  bus_close(&bus);
-  return 0;
-
-fail:
-  perror("write");
-  bus_close(&bus);
-  return 1;
-@}
-@end example
-
-
-
-@node Daemon-dependencies
-@section Daemon-dependencies
-
-This example shows how bus can be used in an init system
-to provide ``aggressivly'' parallel startup of daemons.
-
-First of, run make to build this example.
-
-To start the example run @command{./init}. It will print in
-red export-statement you may want to run i other terminals.
-You will need to select at least one daemon, for example
-you can run @code{./init d-ntp}. The available pretend
-daemons are: @command{d-network}, @command{d-ntp}, and
-@command{d-ssh}.
-
-When you are done run @command{./cleanup} with @env{BUS_INIT}
-exported with the value printed by @command{./init}.
-
-
-@subsubheading @file{./Makefile}
-@example
-COMMANDS = announce await-ready await-started cleanup  \
-           init require start-daemon test-daemon
-
-all: $@{COMMANDS@}
-%: %.c
-        $@{CC@} -Wall -Wextra -pedantic -std=c99 -lbus -o $@@ $<
-clean:
-        -rm $@{COMMANDS@}
-        -rm -r run
-
-.PHONY: all clean
-@end example
-
-
-@subsubheading @file{./announce.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <stdint.h>
-#include <unistd.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static char arg[4098];
-
-int main(int argc, char *argv[])
-@{
-  bus_t bus;
-  if (argc < 3)
-    return fprintf(stderr, "USAGE: %s state daemon", *argv), 2;
-  t (bus_open(&bus, getenv("BUS_INIT"), BUS_WRONLY));
-  sprintf(arg, "%ji %s %s", (intmax_t)getppid(), argv[1], argv[2]);
-  t (bus_write(&bus, arg, 0));
-  t (bus_close(&bus));
-  return 0;
-
-fail:
-  perror("announce");
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./await-ready.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <stdint.h>
-#include <unistd.h>
-#include <string.h>
-#include <sys/wait.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static char arg[4098];
-static int argc;
-static char **argv;
-static int remaining = 0;
-static char *started = NULL;
-static char msg[BUS_MEMORY_SIZE];
-
-static void announce_wait(pid_t pid)
-@{
-  bus_t bus;
-  int i;
-  t (bus_open(&bus, getenv("BUS_INIT"), BUS_WRONLY));
-  for (i = 1; i < argc; i++) @{
-    if (!started[i]) @{
-      sprintf(arg, "%ji awaiting-ready %s", (intmax_t)pid, argv[i]);
-      t (bus_write(&bus, arg, 0));
-    @}
-  @}
-  t (bus_close(&bus));
-  return;
-
-fail:
-  perror("await-ready");
-@}
-
-static int callback(const char *message, void *user_data)
-@{
-  int i;
-  char *arg2;
-  char *arg3;
-  pid_t pid;
-  pid_t ppid;
-
-  if (!message) @{
-    ppid = getppid();
-    pid = fork();
-    if (pid == 0) @{
-      if (fork() == 0)
-        announce_wait(ppid);
-      exit(0);
-    @} else @{
-      (void) waitpid(pid, NULL, 0);
-      /* @w{@xrm{}Let's pretend everything will go swimmingly.@xtt{}} */
-    @}
-    return 1;
-  @}
-
-  strncpy(msg, message, BUS_MEMORY_SIZE - 1);
-  msg[BUS_MEMORY_SIZE - 1] = 0;
-
-  arg2 = strchr(msg, ' ');
-  if (!arg2)
-    return 1;
-  arg3 = strchr(++arg2, ' ');
-  if (!arg3)
-    return 1;
-  *arg3++ = 0;
-
-  if (strcmp(arg2, "ready"))
-    return 1;
-
-  for (i = 1; i < argc; i++)
-    if (!started[i] && !strcmp(argv[i], arg3))
-      started[i] = 1, remaining--;
-
-  return !!remaining;
-  (void) user_data;
-@}
-
-int main(int argc_, char *argv_[])
-@{
-  bus_t bus;
-  int i;
-
-  argc = argc_;
-  argv = argv_;
-
-  if (argc < 2)
-    return fprintf(stderr, "USAGE: %s daemon...", *argv), 2;
-  t (bus_open(&bus, getenv("BUS_INIT"), BUS_RDONLY));
-  started = calloc(argc, sizeof(char));
-  t (started == NULL);
-
-  started[0] = 1;
-  for (i = 1; i < argc; i++) @{
-    sprintf(arg, "grep '^%s$'"
-                 " <\"$@{XDG_RUNTIME_DIR@}/ready-daemons\""
-                 " >/dev/null",
-            argv[i]);
-    if (!WEXITSTATUS(system(arg)))
-      started[i] = 1;
-    else
-      remaining++;
-  @}
-
-  if (remaining)
-    bus_read(&bus, callback, NULL);
-
-  bus_close(&bus);
-  free(started);
-  return 0;
-
-fail:
-  perror("await-ready");
-  bus_close(&bus);
-  free(started);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./await-started.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <stdint.h>
-#include <unistd.h>
-#include <string.h>
-#include <sys/wait.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static char arg[4098];
-static int argc;
-static char **argv;
-static int remaining = 0;
-static char *started = NULL;
-static char msg[BUS_MEMORY_SIZE];
-
-static void announce_wait(pid_t pid)
-@{
-  bus_t bus;
-  int i;
-  t (bus_open(&bus, getenv("BUS_INIT"), BUS_WRONLY));
-  for (i = 1; i < argc; i++) @{
-    if (!started[i]) @{
-      sprintf(arg, "%ji awaiting-started %s", (intmax_t)pid, argv[i]);
-      t (bus_write(&bus, arg, 0));
-    @}
-  @}
-  t (bus_close(&bus));
-  return;
-
-fail:
-  perror("await-started");
-@}
-
-static int callback(const char *message, void *user_data)
-@{
-  int i;
-  char *arg2;
-  char *arg3;
-  pid_t pid;
-  pid_t ppid;
-
-  if (!message) @{
-    ppid = getppid();
-    pid = fork();
-    if (pid == 0) @{
-      if (fork() == 0)
-        announce_wait(ppid);
-      exit(0);
-    @} else @{
-      (void) waitpid(pid, NULL, 0);
-      /* @w{@xrm{}Let's pretend everything will go swimmingly.@xtt{}} */
-    @}
-    return 1;
-  @}
-
-  strncpy(msg, message, BUS_MEMORY_SIZE - 1);
-  msg[BUS_MEMORY_SIZE - 1] = 0;
-
-  arg2 = strchr(msg, ' ');
-  if (!arg2)
-    return 1;
-  arg3 = strchr(++arg2, ' ');
-  if (!arg3)
-    return 1;
-  *arg3++ = 0;
-
-  if (strcmp(arg2, "started") && strcmp(arg2, "ready"))
-    return 1;
-
-  for (i = 1; i < argc; i++)
-    if (!started[i] && !strcmp(argv[i], arg3))
-      started[i] = 1, remaining--;
-
-  return !!remaining;
-  (void) user_data;
-@}
-
-int main(int argc_, char *argv_[])
-@{
-  bus_t bus;
-  int i;
-
-  argc = argc_;
-  argv = argv_;
-
-  if (argc < 2)
-    return fprintf(stderr, "USAGE: %s daemon...", *argv), 2;
-  t (bus_open(&bus, getenv("BUS_INIT"), BUS_RDONLY));
-  started = calloc(argc, sizeof(char));
-  t (started == NULL);
-
-  started[0] = 1;
-  for (i = 1; i < argc; i++) @{
-    sprintf(arg, "grep '^%s$'"
-                 " <\"$@{XDG_RUNTIME_DIR@}/started-daemons\""
-                 " >/dev/null",
-            argv[i]);
-    if (!WEXITSTATUS(system(arg))) @{
-      started[i] = 1;
-    @} else @{
-      sprintf(arg, "grep '^%s$'"
-                   " <\"$@{XDG_RUNTIME_DIR@}/ready-daemons\""
-                   " >/dev/null",
-              argv[i]);
-      if (!WEXITSTATUS(system(arg)))
-        started[i] = 1;
-      else
-        remaining++;
-    @}
-  @}
-
-  if (remaining)
-    bus_read(&bus, callback, NULL);
-
-  bus_close(&bus);
-  free(started);
-  return 0;
-
-fail:
-  perror("await-started");
-  bus_close(&bus);
-  free(started);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./cleanup.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <stdlib.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-int main()
-@{
-  char *bus_address = getenv("BUS_INIT");
-  if (!bus_address || !*bus_address) @{
-    fprintf(stderr, "$BUS_INIT has not been set, its export statement "
-                    "should have been printed in bold red by ./init\n");
-    return 1;
-  @}
-  t (bus_unlink(bus_address));
-  return 0;
-
-fail:
-  perror("cleanup");
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./d-network}
-@example
-#!/bin/sh
-PATH=.:$PATH
-d=d-network
-
-echo $d: starting
-sleep 2
-echo $d: ready
-announce ready $d
-@end example
-
-
-@subsubheading @file{./d-ntp}
-@example
-#!/bin/sh
-PATH=.:$PATH
-d=d-ntp
-
-require d-network
-echo $d: started
-announce started $d
-await-ready d-network
-echo $d: ready
-announce ready $d
-@end example
-
-
-@subsubheading @file{./d-ssh}
-@example
-#!/bin/sh
-PATH=.:$PATH
-d=d-ssh
-
-require d-network
-echo $d: starting
-sleep 1
-echo $d: started
-announce started $d
-sleep 1
-echo $d: ready
-announce ready $d
-@end example
-
-
-@subsubheading @file{./init.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-#include <sys/wait.h>
-
-#define t(stmt)  if (stmt) goto fail
-#define _2(...)  __VA_ARGS__, __VA_ARGS__
-
-static char msg[BUS_MEMORY_SIZE];
-static int argc;
-static char **argv;
-static char arg[4098];
-
-static void start_daemons()
-@{
-  int i;
-  for (i = 1; i < argc; i++)
-    if (fork() == 0)
-      execl("./start-daemon", "./start-daemon", argv[i], NULL); 
-@}
-
-static int callback(const char *message, void *user_data)
-@{
-  pid_t pid;
-  char *arg2;
-  char *arg3;
-  if (!message) @{
-    pid = fork();
-    t (pid == -1);
-    if (pid == 0) @{
-      if (fork() == 0) @{
-        start_daemons();
-      @}
-      exit(0);
-    @} else @{
-      (void) waitpid(pid, NULL, 0);
-      /* @w{@xrm{}Let's pretend everything will go swimmingly.@xtt{}} */
-    @}
-    return 1;
-  @}
-
-  strncpy(msg, message, BUS_MEMORY_SIZE - 1);
-  msg[BUS_MEMORY_SIZE - 1] = 0;
-
-  pid = fork();
-  t (pid == -1);
-
-  if (pid == 0) @{
-    if (fork() == 0) @{
-      arg2 = strchr(msg, ' ');
-      if (arg2 == NULL)
-        exit(0);
-      arg3 = strchr(++arg2, ' ');
-      if (arg3 == NULL)
-        exit(0);
-      *arg3++ = 0;
-      if (!strcmp(arg2, "require")) @{
-        execl(_2("./start-daemon"), arg3, NULL);
-      @} else if (!strcmp(arg2, "awaiting-started")) @{
-        execl(_2("./test-daemon"), arg3, "started", NULL);
-      @} else if (!strcmp(arg2, "awaiting-ready") ||
-                  !strcmp(arg2, "awaiting")) @{
-        execl(_2("./test-daemon"), arg3, "ready", NULL);
-      @} else if (!strcmp(arg2, "started")) @{
-        sprintf(arg,
-          "grep '^%s\\$' < \"%s\" >/dev/null || echo %s >> \"%s\"",
-          _2(arg3, "$@{XDG_RUNTIME_DIR@}/started-daemons"));
-        execlp(_2("sh"), "-c", arg, NULL);
-      @} else if (!strcmp(arg2, "ready")) @{
-        sprintf(arg,
-          "grep '^%s\\$' < \"%s\" >/dev/null || echo %s >> \"%s\"",
-          _2(arg3, "$@{XDG_RUNTIME_DIR@}/ready-daemons"));
-        execlp(_2("sh"), "-c", arg, NULL);
-      @}
-    @}
-    exit(0);
-  @} else @{
-    (void) waitpid(pid, NULL, 0);
-    /* @w{@xrm{}Let's pretend everything will go swimmingly.@xtt{}} */
-  @}
-
-  return 1;
-  (void) user_data;
-
-fail:
-  perror("init");
-  return -1;
-@}
-
-int main(int argc_, char *argv_[])
-@{
-  char *bus_address = NULL;
-  bus_t bus;
-  argv = argv_;
-  argc = argc_;
-  if (argc < 2) @{
-    fprintf(stderr, "USAGE: %s daemon...\n", *argv);
-    return 1;
-  @}
-  t (setenv("XDG_RUNTIME_DIR", "./run", 1));
-  /* @w{@xrm{}Real init systems with not have the period.@xtt{}} */
-  system("mkdir -p -- \"$@{XDG_RUNTIME_DIR@}\"");
-  system("truncate -s 0 -- \"$@{XDG_RUNTIME_DIR@}/started-daemons\"");
-  system("truncate -s 0 -- \"$@{XDG_RUNTIME_DIR@}/ready-daemons\"");
-  t (bus_create(NULL, 1, &bus_address));
-  fprintf(stderr, "\033[00;01;31mexport BUS_INIT=%s\033[00m\n",
-          bus_address);
-  fprintf(stderr, "\033[00;31mexport XDG_RUNTIME_DIR=./run\033[00m\n");
-  t (setenv("BUS_INIT", bus_address, 1));
-  t (bus_open(&bus, bus_address, BUS_RDONLY));
-  t (bus_read(&bus, callback, NULL));
-  bus_close(&bus);
-  free(bus_address);
-  return 0;
-
-fail:
-  perror("init");
-  bus_close(&bus);
-  free(bus_address);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./require.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <stdint.h>
-#include <unistd.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static char arg[4098];
-
-int main(int argc, char *argv[])
-@{
-  bus_t bus;
-  int i;
-  if (argc < 2)
-    return fprintf(stderr, "USAGE: %s daemon...", *argv), 2;
-  t (bus_open(&bus, getenv("BUS_INIT"), BUS_WRONLY));
-
-  for (i = 1; i < argc; i++) @{
-    sprintf(arg, "grep '^%s$' <\"%s\" >/dev/null",
-            argv[i], "$@{XDG_RUNTIME_DIR@}/started-daemons");
-    if (WEXITSTATUS(system(arg))) @{
-      sprintf(arg, "%ji require %s", (intmax_t)getppid(), argv[i]);
-      t (bus_write(&bus, arg, 0));
-    @}
-  @}
-
-  bus_close(&bus);
-  return 0;
-
-fail:
-  perror("require");
-  bus_close(&bus);
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./start-daemon.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-
-static char arg[4098];
-
-int main(int argc, char *argv[])
-@{
-  if (argc != 2) @{
-    fprintf(stderr, "This program should be called from ./init\n");
-    return 2;
-  @}
-
-  sprintf(arg, "grep '^%s$' <\"%s\" >/dev/null",
-          argv[1], "$@{XDG_RUNTIME_DIR@}/started-daemons");
-  if (!WEXITSTATUS(system(arg)))
-    return 0;
-  sprintf(arg, "grep '^%s$' <\"%s\" >/dev/null",
-          argv[1], "$@{XDG_RUNTIME_DIR@}/ready-daemons");
-  if (!WEXITSTATUS(system(arg)))
-    return 0;
-
-  sprintf(arg, "./%s", argv[1]);
-  execlp(arg, arg, NULL);
-  perror("start-daemon");
-  return 1;
-@}
-@end example
-
-
-@subsubheading @file{./test-daemon.c}
-@example
-#include <bus.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-
-#define t(stmt)  if (stmt) goto fail
-
-static char arg[4098];
-
-int main(int argc, char *argv[])
-@{
-  bus_t bus;
-  if (argc != 3) @{
-    fprintf(stderr, "This program should be called from ./init\n");
-    return 2;
-  @}
-
-retry:
-  sprintf(arg, "grep '^%s$'"
-               " <\"$@{XDG_RUNTIME_DIR@}/%s-daemons\""
-               " >/dev/null",
-          argv[1], argv[2]);
-  if (!WEXITSTATUS(system(arg))) @{
-    t (bus_open(&bus, getenv("BUS_INIT"), BUS_WRONLY));
-    sprintf(arg, "0 %s %s", argv[2], argv[1]);
-    t (bus_write(&bus, arg, 0));
-    bus_close(&bus);
-  @} else if (!strcmp(argv[2], "started")) @{
-    argv[2] = "ready";
-    goto retry;
-  @}
-  return 0;
-
-fail:
-  perror("test-daemon");
-  return 1;
-@}
-@end example
-
-
-
-@node GNU Free Documentation License
-@appendix GNU Free Documentation License
-@include fdl.texinfo
-
-@bye
-