sd_bus_get_fd() and related calls are useful for integrating a bus connection into arbitrary event loops. But sd_bus_set_fd() is quite a different beast, it's for using D-Bus over pre-initialized sockets or pairs of fifos or stuff, i.e. very advanced stuff. Let's split this man page in two, in order not to confuse things needlessly. And while we are at it, let's slightly extend the documentation.
System and Service Manager
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