-D-BUS is a simple IPC library based on messages.
+Sections in this file describe:
+ - introduction and overview
+ - low-level vs. high-level API
+ - version numbers
+ - options to the configure script
+ - ABI stability policy
+
+Introduction
+===
+
+D-Bus is a simple system for interprocess communication and coordination.
-See also the file HACKING for notes of interest to developers working on D-BUS.
+The "and coordination" part is important; D-Bus provides a bus daemon that does things like:
+ - notify applications when other apps exit
+ - start services on demand
+ - support single-instance applications
See http://www.freedesktop.org/software/dbus/ for lots of documentation,
mailing lists, etc.
-Note
+See also the file HACKING for notes of interest to developers working on D-Bus.
+
+If you're considering D-Bus for use in a project, you should be aware
+that D-Bus was designed for a couple of specific use cases, a "system
+bus" and a "desktop session bus." These are documented in more detail
+in the D-Bus specification and FAQ available on the web site.
+
+If your use-case isn't one of these, D-Bus may still be useful, but
+only by accident; so you should evaluate carefully whether D-Bus makes
+sense for your project.
+
+Note: low-level API vs. high-level binding APIs
===
-A core concept of the D-BUS implementation is that "libdbus" is
-intended to be a low-level API, similar to Xlib. Most programmers are
-intended to use the bindings to GLib, Qt, Python, Mono, Java, or
-whatever. These bindings have varying levels of completeness.
+A core concept of the D-Bus implementation is that "libdbus" is
+intended to be a low-level API. Most programmers are intended to use
+the bindings to GLib, Qt, Python, Mono, Java, or whatever. These
+bindings have varying levels of completeness and are maintained as
+separate projects from the main D-Bus package. The main D-Bus package
+contains the low-level libdbus, the bus daemon, and a few command-line
+tools such as dbus-launch.
-Configuration flags
+If you use the low-level API directly, you're signing up for some
+pain. Think of the low-level API as analogous to Xlib or GDI, and the
+high-level API as analogous to Qt/GTK+/HTML.
+
+Version numbers
===
-These are the dbus-specific configuration flags that can be given to
-the ./configure program.
-
- --enable-qt enable Qt-friendly client library (note: Qt4)
- --enable-qt-debug enable Qt-friendly client library, linked to debug
- Qt libraries
- --enable-qt3 enable Qt3-friendly client library
- --enable-glib enable GLib-friendly client library
- --enable-gtk enable GTK-requiring executables
- --enable-tests enable unit test code
- --enable-ansi enable -ansi -pedantic gcc flags
- --enable-verbose-mode support verbose debug mode
- --enable-asserts include assertion checks
- --enable-checks include sanity checks on public API
- --enable-xml-docs build XML documentation (requires xmlto)
- --enable-doxygen-docs build DOXYGEN documentation (requires Doxygen)
- --enable-gcov compile with coverage profiling instrumentation (gcc only)
- --enable-abstract-sockets
- use abstract socket namespace (linux only)
- --enable-gcj build gcj bindings
- --enable-mono build mono bindings
- --enable-mono-docs build mono docs
- --enable-python build python bindings
- --enable-selinux build with SELinux support
- --enable-dnotify build with dnotify support (linux only)
-
- --with-qt-moc=<path> moc for Qt
- --with-qt3-moc=<path> moc for Qt3
- --with-xml=libxml/expat XML library to use
- --with-init-scripts=redhat Style of init scripts to install
- --with-session-socket-dir=dirname Where to put sockets for the per-login-session message bus
- --with-test-socket-dir=dirname Where to put sockets for make check
- --with-system-pid-file=pidfile PID file for systemwide daemon
- --with-system-socket=filename UNIX domain socket for systemwide daemon
- --with-console-auth-dir=dirname directory to check for console ownerhip
- --with-dbus-user=<user> User for running the DBUS daemon (messagebus)
- --with-gnu-ld assume the C compiler uses GNU ld [default=no]
- --with-tags[=TAGS] include additional configurations [automatic]
- --with-x use the X Window System
+D-Bus uses the common "Linux kernel" versioning system, where
+even-numbered minor versions are stable and odd-numbered minor
+versions are development snapshots.
+So for example, development snapshots: 1.1.1, 1.1.2, 1.1.3, 1.3.4
+Stable versions: 1.0, 1.0.1, 1.0.2, 1.2.1, 1.2.3
-API/ABI Policy
+All pre-1.0 versions were development snapshots.
+
+Development snapshots make no ABI stability guarantees for new ABI
+introduced since the last stable release. Development snapshots are
+likely to have more bugs than stable releases, obviously.
+
+Configuration
===
-D-BUS API/ABI and protocol necessarily remain in flux until we are
-sure it will meet the various needs it's intended to meet. This means
-we need to see some significant sample usage in the contexts of GNOME,
-KDE, desktop applications, and systemwide uses such as print queue
-monitoring, hotplug events, or whatever. We need the flexibility to
-incorporate feedback from this sample usage.
+dbus could be build by using autotools or cmake.
+
+When using autotools the configure step is initiated by running ./configure
+with or without additional configuration flags.
+
+When using cmake the configure step is initiated by running the cmake
+program with or without additional configuration flags.
+
+Configuration flags
+===
-Once we feel confident in the protocol and the API, we will release a
-version 1.0. At that point, the intent is:
+When using autotools, run "./configure --help" to see the possible
+configuration options and environment variables.
+
+When using cmake, inspect README.cmake to see the possible
+configuration options and environment variables.
+
+API/ABI Policy
+===
+
+Now that D-Bus has reached version 1.0, the objective is that all
+applications dynamically linked to libdbus will continue working
+indefinitely with the most recent system and session bus daemons.
- The protocol will never be broken again; any message bus should
work with any client forever. However, extensions are possible
it will always be possible to compile against and use the older
API, and apps will always get the API they expect.
-Until 1.0 is released, feedback that requires API changes may be
-incorporated into D-BUS. This may break the API, the ABI, the
-protocol, or all three.
+Interfaces can and probably will be _added_. This means both new
+functions and types in libdbus, and new methods exported to
+applications by the bus daemon.
+
+The above policy is intended to make D-Bus as API-stable as other
+widely-used libraries (such as GTK+, Qt, Xlib, or your favorite
+example). If you have questions or concerns they are very welcome on
+the D-Bus mailing list.
+
+NOTE ABOUT DEVELOPMENT SNAPSHOTS AND VERSIONING
+
+Odd-numbered minor releases (1.1.x, 1.3.x, 2.1.x, etc. -
+major.minor.micro) are devel snapshots for testing, and any new ABI
+they introduce relative to the last stable version is subject to
+change during the development cycle.
-To avoid a huge soname, the plan is to increment the soname only
-between official stable releases, not with every development snapshot.
-Versions numbered 0.x are considered development snapshots.
+Any ABI found in a stable release, however, is frozen.
-Until 1.0 is released, you have to define -DDBUS_API_SUBJECT_TO_CHANGE
-just as a safety check to be sure everyone is aware of this API/ABI
-policy and has the right expectations.
+ABI will not be added in a stable series if we can help it. i.e. the
+ABI of 1.2.0 and 1.2.5 you can expect to be the same, while the ABI of
+1.4.x may add more stuff not found in 1.2.x.
-We do need people to test the APIs, so please do use the development
-snapshots of D-BUS. They are intended to work and we do actively
-address bugs.
+NOTE ABOUT STATIC LINKING
+
+We are not yet firmly freezing all runtime dependencies of the libdbus
+library. For example, the library may read certain files as part of
+its implementation, and these files may move around between versions.
+
+As a result, we don't yet recommend statically linking to
+libdbus. Also, reimplementations of the protocol from scratch might
+have to work to stay in sync with how libdbus behaves.
+
+To lock things down and declare static linking and reimplementation to
+be safe, we'd like to see all the internal dependencies of libdbus
+(for example, files read) well-documented in the specification, and
+we'd like to have a high degree of confidence that these dependencies
+are supportable over the long term and extensible where required.
+
+NOTE ABOUT HIGH-LEVEL BINDINGS
+
+Note that the high-level bindings are _separate projects_ from the
+main D-Bus package, and have their own release cycles, levels of
+maturity, and ABI stability policies. Please consult the documentation
+for your binding.
+
+Bootstrapping D-Bus on new platforms
+===
-However, if you're shipping a commercial binary-only application that
-needs to keep running on M future versions of N operating systems, you
-might want to include your own copy of D-BUS rather than relying on
-the installed copy, for example.
+A full build of D-Bus, with all regression tests enabled and run, has some
+dependencies which themselves depend on D-Bus, either for compilation or
+for some of *their* regression tests: GLib, dbus-glib and dbus-python are
+currently affected.
+
+To avoid circular dependencies, when bootstrapping D-Bus for the first time
+on a new OS or CPU architecture, you can either cross-compile some of
+those components, or choose the build order and options carefully:
+
+* build and install D-Bus without tests
+ - do not use the --enable-modular-tests=yes configure option
+ - do not use the --enable-tests=yes configure option
+* build and install GLib, again without tests
+* use those versions of libdbus and GLib to build and install dbus-glib
+* ... and use those to install dbus-python
+* rebuild libdbus; this time you can run all of the tests
+* rebuild GLib; this time you can run all of the tests
projects / platform / upstream / dbus.git / blobdiff