KDBUS To Be Included In The Linux 4.1 Kernel
KDBUS is effectively D-Bus in the Linux kernel for high-performance and secure IPC with the kernel. KDBUS has been especially sought after by systemd developers, is being used for new Linux sandboxing of apps, and PulseAudio will likely end up using it for data transmission, among many other potential use-cases.
With KDBUS in the kernel, there's better performance than if it were in user-space, the security model is better, it takes care of some race conditions than dealing with it in user-space, and various other benefits. The positives of KDBUS are outlined in the KDBUS pull request for Linux 4.1.
Originally KDBUS was planned for the mainline kernel in 2014 but it didn't make it and ended up going through four versions of the patches that were evaluated by other kernel developers. Greg KH noted in the pull request, "There has been a few complaints about the code, notably from people who don't like the use of metadata in the bus messages. That is actually one of the main features here, as we can get this data in a secure and reliable way, and it's something that userspace requires today. So while it does look 'odd' to people who are not familiar with dbus, this is something that finally fixes a number of almost unfixable races in the current dbus implementations."
KDBUS amounts to over 34,000 lines of new code in the Linux kernel.