It _is_ a hassle, and you should have a need for that level of synchronicity. We did it in our team for an in-vehicle network, with the vehicle GPS reciever as the network PTP time master and we figured how to access the ethernet PTP register both from userspace and from the kernel. Kernel for the system clock, user space to avoid latencies from kernel Userland interaction in some high precision real time task. It was a major effort and it required low level hackery way above my personal head.