[TUHS] Ideas for a Unix paper I'm writing

Nick Downing downing.nick+tuhs at gmail.com
Tue Jun 28 10:32:58 AEST 2011

I think you definitely need to say that the idea of file descriptors
in the unix API anticipated the current style (fad?) of
object-oriented programming by about 20 years, languages like
Smalltalk/C++, more recently java/ruby, use opaque objects with
polymorphism to provide services, which is exactly what unix does, an
object hierarchy would look something like:
- read/write capable (file descriptor) objects
  - seek capable (storage) objects
    - truncate capable (file) objects
    - non truncate capable (block) objects
  - non seek capable (stream) objects
    - pipes
    - sockets
      - stream oriented sockets
      - datagram oriented sockets
    - terminals
For terminals, the extension to the API over the basic read/write
capable object is via an ioctl, whereas for sockets it is via its own
API (connect/accept/listen/etc), but conceptually there is no reason
why read/write/lseek/etc couldn't be ioctls as well, since the mapping
from userspace calls (such as lseek or stty/gtty) to syscalls is up to
the standard library.  pipe() is a java-style constructor, whereas
socket() or open() is conceptually a static factory as it can return
different types of objects depending on the request, the constructors
for the corresponding objects are conceptually private constructors.
An errno is basically a checked exception that can be thrown, each
syscall effectively has a java style "throws ..." clause and well
designed userland code catches or rethrows these.
cheers, Nick

On Tue, Jun 28, 2011 at 10:11 AM, Warren Toomey <wkt at tuhs.org> wrote:
> All, IEEE Spectrum have asked me to write a paper on Unix to celebrate the
> 40th anniversary of the release of 1st Edition in November 1971. I'm after
> ideas & suggestions!
> I think my general thrust is that Unix is an elegant design, and the
> design elements are still relevant today. The implementation is mostly
> irrelevant (consider how much the code has changed from assembly -> C,
> from the simple data structures in V7 through to current BSD), but the
> original API is classic. Note that about 28 of the 1st Ed syscalls are
> retained in current BSDs and Linux, and with the same syscall numbers.
> I'm having some trouble thinking of the right way to explain what is
> an elegant design at the OS/syscall level, so any inspirations/ideas
> would be most welcome. I might highlight a couple of syscall groups:
> open/close/read/write, and fork/exec/exit/wait.
> If you have any references/URLs you think I should look at, please
> pass them on to me.
> I'm also trying to chase down some quotes; my memory seems to be failing me
> but I'm sure I've seen these somewhere:
>  - in a paper, I think by Thompson & Ritchie, where they assert that the
>   kernel should provide no more than the most minimal services to the
>   userland programs. I thought this was the CACM paper, but I can't spot
>   this bit. Maybe it's in Thompson's preface to the Lions Commentary,
>   of which my copy is elsewere at present.
>  - I'm sure I remember someome (Kernighan?) say that Ritchie encouraged
>   them to espouse the use of processes as context switching was cheap,
>   but later measurements showed that in fact it wasn't that cheap in
>   the early versions of Unix.
> Anyway, if you can think of good ideas/references about the elegance of
> Unix, especially from the design perspective, I would much appreciate them.
> Cheers,
>        Warren
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