Ron Natalie: It's a violation of the network layering concept to require or even allow the user to bind the application data streams to a physical device. ===== Oh, come on. If you mean an applications programmer shouldn't have to wallow in low-level network details, I agree. That's one of the reasons I think the socket interface now standard in nearly every UNIX is an abomination. It reminds me of the binary data structures you had to assemble just to open a file in TOPS-10, only ten times worse. But if you mean it's a violation of layering for the kernel to expose the pieces and let user-mode code to the work, I strongly disagree. By that argument, the very idea of inetd is an abomination. Possibly even the ifconfig command. And don't even get the hypothetical you started on microkernels. User-mode code for device drivers or file systems? Outrageous violation of layering! Send in the New Jersey Inquisition!! Or perhaps you misunderstand how it all works. Device files for Ethernet devices, /dev/ip*, and so on are like those for disk devices: you could allow anyone to read and write them, but in practice you probably wouldn't: you'd restrict access to the super-user and perhaps a special group to admit some sort of privilege reduction (like the group allowed to read disks on some systems, or to read /dev/kmem). That parts of the stack are assembled in user mode is a feature, not a bug. The one glaring flaw, as I said, is that no permissions are checked when pushing a stream line discipline onto a file. I think that happened because when Dennis first wrote the code, he was thinking about modules to implement canonical-tty semantics, or to invoke the very-different Datakit networking model. It's a fundamental flaw, though. I have had thoughts about fixing it, but never enough time nor enough motivation. (My technical mind is pretty much filled up by what I am paid to do these days; I haven't done much hobby computing in years.) Norman Wilson Toronto ON