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Diffstat (limited to 'README')
| -rw-r--r-- | README | 129 |
1 files changed, 97 insertions, 32 deletions
@@ -1,17 +1,64 @@ -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. + +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 +=== + +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 + +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 flags === @@ -48,15 +95,9 @@ the ./configure program. API/ABI Policy === -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. - -Once we feel confident in the protocol and the API, we will release a -version 1.0. At that point, the intent is: +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 @@ -67,23 +108,47 @@ version 1.0. At that point, the intent is: 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. + +Any ABI found in a stable release, however, is frozen. + +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. + +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. -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. +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. -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. +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. -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 HIGH-LEVEL BINDINGS -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. +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. |