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diff --git a/bus.texinfo b/bus.texinfo new file mode 100644 index 0000000..be50cea --- /dev/null +++ b/bus.texinfo @@ -0,0 +1,2079 @@ +\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 + |