>>132
Instead of speculating.... actually, you're a troll. I fell for it.
Instead of speculating about what? Here's the source for cat:
http://swtch.com/usr/local/plan9/src/cmd/cat.c, here's one for read:
http://swtch.com/usr/local/plan9/src/cmd/read.c
There's nothing special the OS does directly, rather it's all handled by the device. The device writes the code in a suitable way, depending on its nature.
So if the device does not preserve the guarantees made in the documentation, then documentation ends up being wrong, the retardation you can see in the read(1) code ends up being pointless, and all userspace programs written by naive morons who trusted the documentation are broken.
I don't quite follow what you're trying to prove.