Kernel space: udev rules, but whose?
Once upon a time, a Linux distribution would be installed with a /dev directory fully populated with device files. Most of them represented hardware which would never be present on the installed system, but they needed to be there just in case. Toward the end of this era, it was not uncommon to find systems with around 20,000 special files in /dev, and the number continued to grow. This scheme was unwieldy at best, and the growing number of hotpluggable devices (and devices in general) threatened to make the whole structure collapse under its own weight. Something, clearly, needed to be done.