[TUHS] Ethernet in /dev (was Re: Were all of you.. Hippies?)

Norman Wilson norman at oclsc.org
Fri Mar 31 05:24:25 AEST 2017


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


More information about the TUHS mailing list