Heh.. Hopefully someone else will pitch in here, as the programming I do rarely, if ever, uses libraries other than standard libc.

But for hotplug events, the kernel can feed them to userspace using whatever command is echoed into /proc/sys/kernel/hotplug (that's the old method) and/or via a netlink interface.

The advantage of netlink is that the events will generally arrive in time sequence, which cannot be said of the other method.

Libraries like libhal, and daemons like udevd, presumably sit on top of one or both of those.

Cheers