1Sections 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 8Introduction 9=== 10 11D-Bus is a simple system for interprocess communication and coordination. 12 13The "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 18See http://www.freedesktop.org/software/dbus/ for lots of documentation, 19mailing lists, etc. 20 21See also the file HACKING for notes of interest to developers working on D-Bus. 22 23If you're considering D-Bus for use in a project, you should be aware 24that D-Bus was designed for a couple of specific use cases, a "system 25bus" and a "desktop session bus." These are documented in more detail 26in the D-Bus specification and FAQ available on the web site. 27 28If your use-case isn't one of these, D-Bus may still be useful, but 29only by accident; so you should evaluate carefully whether D-Bus makes 30sense for your project. 31 32Note: low-level API vs. high-level binding APIs 33=== 34 35A core concept of the D-Bus implementation is that "libdbus" is 36intended to be a low-level API. Most programmers are intended to use 37the bindings to GLib, Qt, Python, Mono, Java, or whatever. These 38bindings have varying levels of completeness and are maintained as 39separate projects from the main D-Bus package. The main D-Bus package 40contains the low-level libdbus, the bus daemon, and a few command-line 41tools such as dbus-launch. 42 43If you use the low-level API directly, you're signing up for some 44pain. Think of the low-level API as analogous to Xlib or GDI, and the 45high-level API as analogous to Qt/GTK+/HTML. 46 47Version numbers 48=== 49 50D-Bus uses the common "Linux kernel" versioning system, where 51even-numbered minor versions are stable and odd-numbered minor 52versions are development snapshots. 53 54So for example, development snapshots: 1.1.1, 1.1.2, 1.1.3, 1.3.4 55Stable versions: 1.0, 1.0.1, 1.0.2, 1.2.1, 1.2.3 56 57All pre-1.0 versions were development snapshots. 58 59Development snapshots make no ABI stability guarantees for new ABI 60introduced since the last stable release. Development snapshots are 61likely to have more bugs than stable releases, obviously. 62 63Configuration flags 64=== 65 66These are the dbus-specific configuration flags that can be given to 67the ./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 94API/ABI Policy 95=== 96 97Now that D-Bus has reached version 1.0, the objective is that all 98applications dynamically linked to libdbus will continue working 99indefinitely 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 110Interfaces can and probably will be _added_. This means both new 111functions and types in libdbus, and new methods exported to 112applications by the bus daemon. 113 114The above policy is intended to make D-Bus as API-stable as other 115widely-used libraries (such as GTK+, Qt, Xlib, or your favorite 116example). If you have questions or concerns they are very welcome on 117the D-Bus mailing list. 118 119NOTE ABOUT DEVELOPMENT SNAPSHOTS AND VERSIONING 120 121Odd-numbered minor releases (1.1.x, 1.3.x, 2.1.x, etc. - 122major.minor.micro) are devel snapshots for testing, and any new ABI 123they introduce relative to the last stable version is subject to 124change during the development cycle. 125 126Any ABI found in a stable release, however, is frozen. 127 128ABI will not be added in a stable series if we can help it. i.e. the 129ABI of 1.2.0 and 1.2.5 you can expect to be the same, while the ABI of 1301.4.x may add more stuff not found in 1.2.x. 131 132NOTE ABOUT STATIC LINKING 133 134We are not yet firmly freezing all runtime dependencies of the libdbus 135library. For example, the library may read certain files as part of 136its implementation, and these files may move around between versions. 137 138As a result, we don't yet recommend statically linking to 139libdbus. Also, reimplementations of the protocol from scratch might 140have to work to stay in sync with how libdbus behaves. 141 142To lock things down and declare static linking and reimplementation to 143be safe, we'd like to see all the internal dependencies of libdbus 144(for example, files read) well-documented in the specification, and 145we'd like to have a high degree of confidence that these dependencies 146are supportable over the long term and extensible where required. 147 148NOTE ABOUT HIGH-LEVEL BINDINGS 149 150Note that the high-level bindings are _separate projects_ from the 151main D-Bus package, and have their own release cycles, levels of 152maturity, and ABI stability policies. Please consult the documentation 153for your binding. 154