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 flags 64 === 65 66 These are the dbus-specific configuration flags that can be given to 67 the ./configure program. 68 69 --enable-tests enable unit test code 70 --enable-verbose-mode support verbose debug mode 71 --enable-asserts include assertion checks 72 --enable-checks include sanity checks on public API 73 --enable-xml-docs build XML documentation (requires xmlto) 74 --enable-doxygen-docs build DOXYGEN documentation (requires Doxygen) 75 --enable-gcov compile with coverage profiling instrumentation (gcc only) 76 --enable-abstract-sockets 77 use abstract socket namespace (linux only) 78 --enable-selinux build with SELinux support 79 --enable-dnotify build with dnotify support (linux only) 80 --enable-kqueue build with kqueue support (*BSD only) 81 --with-xml=libxml/expat XML library to use 82 --with-init-scripts=redhat Style of init scripts to install 83 --with-session-socket-dir=dirname Where to put sockets for the per-login-session message bus 84 --with-test-socket-dir=dirname Where to put sockets for make check 85 --with-system-pid-file=pidfile PID file for systemwide daemon 86 --with-system-socket=filename UNIX domain socket for systemwide daemon 87 --with-console-auth-dir=dirname directory to check for console ownerhip 88 --with-dbus-user=<user> User for running the DBUS daemon (messagebus) 89 --with-gnu-ld assume the C compiler uses GNU ld [default=no] 90 --with-tags[=TAGS] include additional configurations [automatic] 91 --with-x use the X Window System 92 93 94 API/ABI Policy 95 === 96 97 Now that D-Bus has reached version 1.0, the objective is that all 98 applications dynamically linked to libdbus will continue working 99 indefinitely with the most recent system and session bus daemons. 100 101 - The protocol will never be broken again; any message bus should 102 work with any client forever. However, extensions are possible 103 where the protocol is extensible. 104 105 - If the library API is modified incompatibly, we will rename it 106 as in http://ometer.com/parallel.html - in other words, 107 it will always be possible to compile against and use the older 108 API, and apps will always get the API they expect. 109 110 Interfaces can and probably will be _added_. This means both new 111 functions and types in libdbus, and new methods exported to 112 applications by the bus daemon. 113 114 The above policy is intended to make D-Bus as API-stable as other 115 widely-used libraries (such as GTK+, Qt, Xlib, or your favorite 116 example). If you have questions or concerns they are very welcome on 117 the D-Bus mailing list. 118 119 NOTE ABOUT DEVELOPMENT SNAPSHOTS AND VERSIONING 120 121 Odd-numbered minor releases (1.1.x, 1.3.x, 2.1.x, etc. - 122 major.minor.micro) are devel snapshots for testing, and any new ABI 123 they introduce relative to the last stable version is subject to 124 change during the development cycle. 125 126 Any ABI found in a stable release, however, is frozen. 127 128 ABI will not be added in a stable series if we can help it. i.e. the 129 ABI of 1.2.0 and 1.2.5 you can expect to be the same, while the ABI of 130 1.4.x may add more stuff not found in 1.2.x. 131 132 NOTE ABOUT STATIC LINKING 133 134 We are not yet firmly freezing all runtime dependencies of the libdbus 135 library. For example, the library may read certain files as part of 136 its implementation, and these files may move around between versions. 137 138 As a result, we don't yet recommend statically linking to 139 libdbus. Also, reimplementations of the protocol from scratch might 140 have to work to stay in sync with how libdbus behaves. 141 142 To lock things down and declare static linking and reimplementation to 143 be safe, we'd like to see all the internal dependencies of libdbus 144 (for example, files read) well-documented in the specification, and 145 we'd like to have a high degree of confidence that these dependencies 146 are supportable over the long term and extensible where required. 147 148 NOTE ABOUT HIGH-LEVEL BINDINGS 149 150 Note that the high-level bindings are _separate projects_ from the 151 main D-Bus package, and have their own release cycles, levels of 152 maturity, and ABI stability policies. Please consult the documentation 153 for your binding. 154
