About: D-Bus is an inter-process communication (IPC) system, allowing multiple, concurrently-running applications to communicate with one another. D-Bus supplies both a system daemon and a per-user-login-session daemon. Development version.
Fossies Dox: dbus-1.11.4.tar.gz ("inofficial" and yet experimental doxygen-generated source code documentation)
This manual documents the low-level D-Bus C API. If you use this low-level API directly, you're signing up for some pain.
There are several other places to look for D-Bus information, such as the tutorial and the specification; those can be found at the D-Bus website. If you're interested in a sysadmin or package maintainer's perspective on the dbus-daemon itself and its configuration, be sure to check out the man pages as well.
The low-level API documented in this manual deliberately lacks most convenience functions - those are left up to higher-level libraries based on frameworks such as GLib, Qt, Python, Mono, Java, etc. These higher-level libraries (often called "D-Bus bindings") have features such as object systems and main loops that allow a much more convenient API.
The low-level API also contains plenty of clutter to support integration with arbitrary object systems, languages, main loops, and so forth. These features add a lot of noise to the API that you probably don't care about unless you're coding a binding.
This manual also contains docs for D-Bus internals, so you can use it to get oriented to the D-Bus source code if you're interested in patching the code. You should also read the file HACKING which comes with the source code if you plan to contribute to D-Bus.
As you read the code, you can identify internal D-Bus functions because they start with an underscore ('_') character. Also, any identifier or macro that lacks a DBus, dbus_, or DBUS_ namepace prefix is internal, with a couple of exceptions such as NULL, TRUE, and FALSE.