Standards Update, IEEE 1003.4: Real-time Extensions

[Dan Bernstein]

Submitted-by: brnstnd at kramden.acf.nyu.edu (Dan Bernstein)

In article <529 at usenix.ORG> chip at tct.uucp (Chip Salzenberg) writes:
> According to fouts at bozeman.bozeman.ingr (Martin Fouts):
> >However, the presences of the proc file system is not a strong arguement
> >for the inclusion of othere features in the file system.
> I disagree.  I consider it an excellent example of how the designers
> of Unix realize that all named objects potentially visible to more
> than one process belong in the filesystem namespace.

I disagree. I consider it an excellent example of how the designers of
UNIX realize that all *reliable*, *static*, *local* (or virtually local)
I/O objects potentially visible to more than one process belong in the
filesystem namespace.

/dev/proc, for example, is reliable---there's no chance of arbitrary
failure. It's static---processes have inertia, and stick around until
they take the positive action of exit()ing. And it's local---you don't
have an arbitrary delay before seeing the information. So it's a
perfectly fine thing to include in the filesystem without hesitation.

Objects that aren't reliable, or aren't static, or aren't local, also
aren't necessarily sensible targets of an open(). Some of them might fit
well, but each has to be considered on its own merits.

> So, how do we program in such a system?  We use its elegant interface
> -- or should I say "interfaces"?  Plain files, devices, IPCs, and
> network connections each have a semantically accurate interface, which
> unfortunately makes it different from all others.

The single UNIX interface is the file descriptor. You can read() or
write() reasonable I/O objects through file descriptors. Very few
programs---the shell is a counterexample---need to worry about what it
takes to set up those file descriptors. Very few programs---stty is a
counterexample---need to know the ioctl()s or other functions that
control the I/O more precisely. What is your complaint?

---Dan

Volume-Number: Volume 21, Number 136