KDBUS in FreeBSD

Things in the Linux world (e.g. GNOME, systemd) are increasingly moving towards requiring kdbus support from the kernel. This page contains notes on what a FreeBSD implementation will look like.

The FreeBSD implementation has the following basic requirements:

• Source compatibility with Linux kdbus
• Integration with Capsicum and other FreeBSD features (audit, MAC)
• Kernel changes only where required for performance
• Use existing UNIX APIs where possible (e.g. aio_read() for one-copy I/O).

Kdbus on Linux has two major components: IPC and namespace management. The IPC component allows:

• Support point-to-point and multicast messaging
• Fast one-copy messaging
• Message-oriented protocol
• Userspace and kernel endpoints
• Messages contain bytes and / or file descriptors

The namespace management is responsible for creating hierarchies (under /dev in Linux) containing the busses.

Endpoints should be represented by a new kind of file descriptor, which should support all of the capsicum restrictions. These should be either anonymous or present in the filesystem. Placing them in the filesystem allows a userspace component to manage the namespace. Anonymous endpoints allow integration with Capsicum by providing endpoints to sandboxed processes without ever placing them in a global namespace.