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Date: Thu, 27 Dec 2001 16:49:26 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: Tim Van Holder <tim DOT van DOT holder AT pandora DOT be>
cc: djgpp-workers AT delorie DOT com, "'Charles Sandmann'" <sandmann AT clio DOT rice DOT edu>
Subject: RE: lfn from scratch...
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On Thu, 27 Dec 2001, Tim Van Holder wrote:

> Agreed.  A DOS 'cd' is impossible, as that never changes 'drives'.
> But an NT 'pushd' is possible.  Since our 'chdir' is supposed to be
> Unixy, 'chdir c:/foo' should be more like pushd (i.e. 'c:; cd /foo'),
> and so UNCs should be chdir()able.

The problem is, our chdir calls a DOS function to change drives, and that 
function needs a drive letter.

To do the equivalent of pushd, we need to know what system call to 
invoke, and how to compute its arguments.  Do you happen to know that?

> > It is also a misfeature in general to have a directory which cannot be
> > chdir'ed into.  We cannot expect to get away with that.
> 
> Well, I suppose we could have stat/fstat not set the 'executable' bit
> for UNC dirs; that indicates you can't chdir into them.

That won't help, I think: our chdir doesn't test that bit (and does not 
call stat).  The equivalent of "test -d" (IIRC, access(D_OK)) also 
doesn't check that.  These and other cases look at the directory 
attribute bit, not at the execute bit.

In any case, even if chdir knows in advance that it cannot chdir, all you 
get is perhaps a more intelligent error message.  Application code will 
still not expect such calamities.

> > Perhaps you could look into what Windows programs, such as COMMAND.COM
> > or CMD.EXE, do when you type "cd \\cws333\c$\djgpp".
> 
> cmd.exe maps a temporary drive letter
> to the UNC 'drive' and uses that

Perhaps we could do the same.  IIRC, the system call to map a drive is 
something we can issue.  Functions 5F03h and 5F04h of Int 21h seem like a 
good beginning.