Re: Why side-effects on open(2) are evil. (was Re: [RFD w/info-PATCH]device arguments from lookup)

Daniel Phillips
2001-05-22T20:21:57Z

On Tuesday 22 May 2001 19:49, Oliver Xymoron wrote:
> On Tue, 22 May 2001, Daniel Phillips wrote:
> > > I don't think it's likely to be even workable. Just consider the
> > > directory entry for a moment - is it going to be marked d or
> > > [cb]?
> >
> > It's going to be marked 'd', it's a directory, not a file.
>
> Are we talking about the same proposal? The one where I can open
> /dev/dsp and /dev/dsp/ctl? But I can still do 'cat /dev/hda >
> /dev/dsp'?

We already support read/write on directories in the VFS, that's not a
problem.

> It's still a file. If it's not a file anymore, it ain't UNIX.

It's a file with the directory bit set, I believe that's UNIX.

> > > If it doesn't have the directory bit set, Midnight commander
> > > won't let me look at it, and I wouldn't blame cd or ls for
> > > complaining. If it does have the 'd' bit set, I wouldn't blame
> > > cp, tar, find, or a million other programs if they did the wrong
> > > thing. They've had 30 years to expect that files aren't
> > > directories. They're going to act weird.
> >
> > No problem, it's a directory.
> >
> > > Linus has been kicking this idea around for a couple years now
> > > and it's still a cute solution looking for a problem. It just
> > > doesn't belong in UNIX.
> >
> > Hmm, ok, do we still have any *technical* reasons?
>
> If you define *technical* to not include design, sure.

Sorry, I don't see what you mean, do you mean the design is
difficult?

> Oh, did I mention unnecessary, solvable in userspace?

That's exactly the point: the generic filesystem allows all the
funny-shaped stuff to be dealt with in user space. The
filesystem itself is lovely and clean.

BTW, I didn't realize I was reinventing Linus's wheel, this just
seemed very obvious and natural to me. So I had to believe
there's a technical obstacle somewhere.

Has anyone written code to demonstrate the idea?

--
Daniel