1 Sections in this file describe: 2 - introduction and overview 3 - low-level vs. high-level API 4 - version numbers 5 - options to the configure script 6 - ABI stability policy 7 8 Introduction 9 === 10 11 D-Bus is a simple system for interprocess communication and coordination. 12 13 The "and coordination" part is important; D-Bus provides a bus daemon that does things like: 14 - notify applications when other apps exit 15 - start services on demand 16 - support single-instance applications 17 18 See http://www.freedesktop.org/software/dbus/ for lots of documentation, 19 mailing lists, etc. 20 21 See also the file HACKING for notes of interest to developers working on D-Bus. 22 23 If you're considering D-Bus for use in a project, you should be aware 24 that D-Bus was designed for a couple of specific use cases, a "system 25 bus" and a "desktop session bus." These are documented in more detail 26 in the D-Bus specification and FAQ available on the web site. 27 28 If your use-case isn't one of these, D-Bus may still be useful, but 29 only by accident; so you should evaluate carefully whether D-Bus makes 30 sense for your project. 31 32 Note: low-level API vs. high-level binding APIs 33 === 34 35 A core concept of the D-Bus implementation is that "libdbus" is 36 intended to be a low-level API. Most programmers are intended to use 37 the bindings to GLib, Qt, Python, Mono, Java, or whatever. These 38 bindings have varying levels of completeness and are maintained as 39 separate projects from the main D-Bus package. The main D-Bus package 40 contains the low-level libdbus, the bus daemon, and a few command-line 41 tools such as dbus-launch. 42 43 If you use the low-level API directly, you're signing up for some 44 pain. Think of the low-level API as analogous to Xlib or GDI, and the 45 high-level API as analogous to Qt/GTK+/HTML. 46 47 Version numbers 48 === 49 50 D-Bus uses the common "Linux kernel" versioning system, where 51 even-numbered minor versions are stable and odd-numbered minor 52 versions are development snapshots. 53 54 So for example, development snapshots: 1.1.1, 1.1.2, 1.1.3, 1.3.4 55 Stable versions: 1.0, 1.0.1, 1.0.2, 1.2.1, 1.2.3 56 57 All pre-1.0 versions were development snapshots. 58 59 Development snapshots make no ABI stability guarantees for new ABI 60 introduced since the last stable release. Development snapshots are 61 likely to have more bugs than stable releases, obviously. 62 63 Configuration 64 === 65 66 dbus could be build by using autotools or cmake. 67 68 When using autotools the configure step is initiated by running ./configure 69 with our without additional configuration flags. 70 71 When using cmake the configure step is initiated by running the cmake 72 program with our without additional configuration flags. 73 74 Configuration flags 75 === 76 77 When using autools the dbus-specific configuration flags that can be given to 78 the ./configure program are these 79 80 --enable-tests enable unit test code 81 --enable-verbose-mode support verbose debug mode 82 --enable-asserts include assertion checks 83 --enable-checks include sanity checks on public API 84 --enable-xml-docs build XML documentation (requires xmlto) 85 --enable-doxygen-docs build DOXYGEN documentation (requires Doxygen) 86 --enable-gcov compile with coverage profiling instrumentation (gcc only) 87 --enable-abstract-sockets use abstract socket namespace (linux only) 88 --enable-selinux build with SELinux support 89 --enable-dnotify build with dnotify support (linux only) 90 --enable-kqueue build with kqueue support (*BSD only) 91 --with-xml=libxml/expat XML library to use 92 --with-init-scripts=redhat Style of init scripts to install 93 --with-session-socket-dir=dirname Where to put sockets for the per-login-session message bus 94 --with-test-socket-dir=dirname Where to put sockets for make check 95 --with-system-pid-file=pidfile PID file for systemwide daemon 96 --with-system-socket=filename UNIX domain socket for systemwide daemon 97 --with-console-auth-dir=dirname directory to check for console ownerhip 98 --with-dbus-user=<user> User for running the DBUS daemon (messagebus) 99 --with-gnu-ld assume the C compiler uses GNU ld [default=no] 100 --with-tags[=TAGS] include additional configurations [automatic] 101 --with-x use the X Window System 102 103 When using the cmake build system the dbus-specific configuration flags that can be given 104 to the cmake program are these (use -D<key>=<value> on command line) 105 106 CMAKE_BUILD_TYPE set dbus build mode - one of Debug|Release|RelWithDebInfo|MinSizeRel 107 DBUS_BUILD_TESTS enable unit test code default=ON 108 DBUS_BUILD_X11 Build X11-dependent code default=ON 109 HAVE_CONSOLE_OWNER_FILE enable console owner file (solaris only) ) default=ON 110 DBUS_DISABLE_ASSERTS Disable assertion checking default=OFF 111 DBUS_DISABLE_CHECKS Disable public API sanity checking default=OFF 112 DBUS_ENABLE_ABSTRACT_SOCKETS enable support for abstract sockets (linux only) default=ON 113 DBUS_ENABLE_ANSI enable -ansi -pedantic gcc flags default=OFF 114 DBUS_ENABLE_DNOTIFY build with dnotify support (linux only) default=ON 115 DBUS_ENABLE_VERBOSE_MODE support verbose debug mode default=ON 116 DBUS_ENABLE_DOXYGEN_DOCS build DOXYGEN documentation (requires Doxygen) default=ON 117 DBUS_GCOV_ENABLED compile with coverage profiling instrumentation (gcc only) default=OFF 118 DBUS_INSTALL_SYSTEM_LIBS install required system libraries default (windows only) =OFF 119 DBUS_USE_EXPAT Use expat (== ON) or libxml2 (==OFF) default=ON [1] 120 DBUS_USE_NONCE_TCP_DEFAULT_ADDRESS Use nonce tcp default address default=OFF 121 DBUS_USE_OUTPUT_DEBUG_STRING enable win32 debug port for message output default=OFF 122 123 [1] requires installed development package of the related dependency 124 125 126 API/ABI Policy 127 === 128 129 Now that D-Bus has reached version 1.0, the objective is that all 130 applications dynamically linked to libdbus will continue working 131 indefinitely with the most recent system and session bus daemons. 132 133 - The protocol will never be broken again; any message bus should 134 work with any client forever. However, extensions are possible 135 where the protocol is extensible. 136 137 - If the library API is modified incompatibly, we will rename it 138 as in http://ometer.com/parallel.html - in other words, 139 it will always be possible to compile against and use the older 140 API, and apps will always get the API they expect. 141 142 Interfaces can and probably will be _added_. This means both new 143 functions and types in libdbus, and new methods exported to 144 applications by the bus daemon. 145 146 The above policy is intended to make D-Bus as API-stable as other 147 widely-used libraries (such as GTK+, Qt, Xlib, or your favorite 148 example). If you have questions or concerns they are very welcome on 149 the D-Bus mailing list. 150 151 NOTE ABOUT DEVELOPMENT SNAPSHOTS AND VERSIONING 152 153 Odd-numbered minor releases (1.1.x, 1.3.x, 2.1.x, etc. - 154 major.minor.micro) are devel snapshots for testing, and any new ABI 155 they introduce relative to the last stable version is subject to 156 change during the development cycle. 157 158 Any ABI found in a stable release, however, is frozen. 159 160 ABI will not be added in a stable series if we can help it. i.e. the 161 ABI of 1.2.0 and 1.2.5 you can expect to be the same, while the ABI of 162 1.4.x may add more stuff not found in 1.2.x. 163 164 NOTE ABOUT STATIC LINKING 165 166 We are not yet firmly freezing all runtime dependencies of the libdbus 167 library. For example, the library may read certain files as part of 168 its implementation, and these files may move around between versions. 169 170 As a result, we don't yet recommend statically linking to 171 libdbus. Also, reimplementations of the protocol from scratch might 172 have to work to stay in sync with how libdbus behaves. 173 174 To lock things down and declare static linking and reimplementation to 175 be safe, we'd like to see all the internal dependencies of libdbus 176 (for example, files read) well-documented in the specification, and 177 we'd like to have a high degree of confidence that these dependencies 178 are supportable over the long term and extensible where required. 179 180 NOTE ABOUT HIGH-LEVEL BINDINGS 181 182 Note that the high-level bindings are _separate projects_ from the 183 main D-Bus package, and have their own release cycles, levels of 184 maturity, and ABI stability policies. Please consult the documentation 185 for your binding. 186
