Sender: vheyndri AT rug DOT ac DOT be
Message-Id: <3503D9F5.1D0E@rug.ac.be>
Date: Mon, 09 Mar 1998 13:00:53 +0100
From: Vik Heyndrickx <Vik DOT Heyndrickx AT rug DOT ac DOT be>
Mime-Version: 1.0
To: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
Cc: djgpp-workers AT delorie DOT com
Subject: Re: Temporary files considered unsafe
References: <Pine DOT SUN DOT 3 DOT 91 DOT 980309130555 DOT 23398A-100000 AT is>
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Eli Zaretskii wrote:
> On Mon, 9 Mar 1998, Vik Heyndrickx wrote:
> > The most
> > sensible mode precisely seems DENY_ALL, but I'll need to test that.
> 
> ``Sensible''?  Since when do we trust Microsoft to do sensible things?
:-)

> > The
> > importance for being able to open a file in a particular sharing mode
> > seems low.
> 
> It's another safeguard, that's all.

What other program could want to open our file for writing?

> > > and the place where DOS puts it (we want it to go to $TMPDIR, for
> > > example).
> >
> > IIRC this can be controlled through the DOS call.
> Which one is that?

The same I was referring to above, you pass a path and DOS appends the
filename for the newly created temp-file.

> > > Won't all first-level programs in different DOS boxes on Windows have the
> > > same PSP address?
> >
> > I though the DOS conventional memory was common to all DOS boxes, or am
> > I so wrong?
> 
> It is not common, it is mapped into all DOS boxes, but it is kept
> separate.  Windows twiddles the memory page directory when it multi-tasks
> DOS apps, so that each DOS app gets a separate address space, but the
> real-mode addresses are the same.

I don't understand "mapped into all DOS boxes" vs. "kept separate".
Either any DOS program has a different "below 640Kb + UMB" address
space, or it has the same.
You imply the first?

The same offsets, different linear addresses, but the same real-mode
addresses for conventional (mapped) memory. So, this means that any DOS
prg runs in the same "below 1Mb" address space? Meaning that a
PSP-segment IS unique?

> > If you are right, what about getpid()?
> 
> DJGPP's `getpid' doesn't use the PSP address.  It reads the BIOS clock
> tick count the first time it is invoked in the given program, then caches
> the value and returns it hence.

Then it most certainly not suits what I want as a unique value, since
two programs can be started in the same 1/18.2s period.

> > > AFAIK, this is the max number of unique names we can *potentially*
> > > generate.
> >
> > Meaning, in the example above 86400 * X ?
> 
> What's X?  Is it the total number of segments below 1MB mark?  

X was the counter value (equivalent to the current counter in
tempnam[e]). This value should prevent from different names to be
generated during the same second by one program.

Because a program cannot create more than X values during the same
second I feel like setting MAX_TEMPNAM = X, but the program potentially
can create 86400 * X in one day. That is why I am so careful about not
setting it to 24 * 60 * 60 * X.

> And how do you account for the truncation to 8+3 namespace?

I simply create filenames that ARE 8+3 (and don't contain '~' BTW), I
don't know why I should make things more complicated?

-- 
 \ Vik /-_-_-_-_-_-_/   
  \___/ Heyndrickx /          
   \ /-_-_-_-_-_-_/