DMARC-Filter: OpenDMARC Filter v1.4.2 delorie.com 5795g6du4154679
Authentication-Results: delorie.com; dmarc=pass (p=none dis=none) header.from=cygwin.com
Authentication-Results: delorie.com; spf=pass smtp.mailfrom=cygwin.com
DKIM-Filter: OpenDKIM Filter v2.11.0 delorie.com 5795g6du4154679
Authentication-Results: delorie.com;
	dkim=pass (1024-bit key, unprotected) header.d=cygwin.com header.i=@cygwin.com header.a=rsa-sha256 header.s=default header.b=yaOKKyX9
X-Recipient: archive-cygwin AT delorie DOT com
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 96E4D3857032
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1754718124;
	bh=cuHGbV/spz/UnIUkDiKJyUeKT+V/51509k8ImLNZe88=;
	h=Date:To:cc:Subject:In-Reply-To:References:List-Id:
	 List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe:
	 From:Reply-To:From;
	b=yaOKKyX9GacXjrYe3JUH1a3X/m+BxyIx0wzDxYJQ57Ke+OC2TZKMAqu0aSVqLLRS+
	 GcPNgmw58i//HiVXWcnlXDv1KCl7OmvGx83kJntGrLU+5TyZGVPmc2dcAKylt9YIz2
	 TnERK/9tBlbkxnqjOaaMSdr7AVmplYZOYsMUDypo=
X-Original-To: cygwin AT cygwin DOT com
Delivered-To: cygwin AT cygwin DOT com
DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 53C473858D29
ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 53C473858D29
ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1754718063; cv=none;
 b=GVozUATxw6QcU/5IP1GRR2vkycbsVHr0JGkLqGeNyLMeh+eMkEJEnc4PoD0SbrZyj0ZmDCmOMtw78c73swxspM5nu9Lq5HzEb9Fk4mOXru/gDnMjmWaKEeXzzpKVAl3AQa17PQ2Lo40tKQx1impkJO/+coG0RJHTJHsUGofUVhg=
ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key;
 t=1754718063; c=relaxed/simple;
 bh=kq3OTNTcVnLR7F+g8VqNr16ZLvHE1H/3LaUvryoCZks=;
 h=DKIM-Signature:Date:From:To:Subject:Message-ID:MIME-Version;
 b=UDKxaXf5yy5jREATqp4k+qMk6ZPLa1Nijt9vDuuc59KlhAwyeKD6f3luG/M+Gg/t0hH6e1plZQXUpzHdR8pbnaPSItyUr05ymtzf+mfD0uVoxwOGvqNhF0zQaPdtDk3v01CzJnl+Tj5hhU6wdku4lNrZgDCve/ka3JhQvq2Oc4g=
ARC-Authentication-Results: i=1; server2.sourceware.org
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 53C473858D29
Date: Fri, 8 Aug 2025 22:33:25 -0700 (PDT)
X-X-Sender: jeremyd AT resin DOT csoft DOT net
To: Brian Inglis via Cygwin <cygwin AT cygwin DOT com>
cc: brian DOT inglis AT systematicsw DOT ab DOT ca
Subject: Re: getting the on-disk case for a path
In-Reply-To: <585f65a8-a675-4a1e-a774-5dc4ff2337f8@systematicsw.ab.ca>
Message-ID: <81c4de12-856c-2d1d-d6bf-ee0fe96f3429@jdrake.com>
References: <36a0093c-fc8b-f268-9cbf-71c1c1268ef7 AT jdrake DOT com>
 <11a5bd41-e977-4f25-9bf8-4917f1c65934 AT towo DOT net>
 <585f65a8-a675-4a1e-a774-5dc4ff2337f8 AT systematicsw DOT ab DOT ca>
MIME-Version: 1.0
X-Content-Filtered-By: Mailman/MimeDel 2.1.30
X-BeenThere: cygwin AT cygwin DOT com
X-Mailman-Version: 2.1.30
Precedence: list
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe: <https://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive: <https://cygwin.com/pipermail/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe: <https://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From: Jeremy Drake via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Jeremy Drake <cygwin AT jdrake DOT com>
Content-Type: text/plain; charset="utf-8"
Errors-To: cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com
Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from base64 to 8bit by delorie.com id 5795g6du4154679

On Fri, 8 Aug 2025, Brian Inglis via Cygwin wrote:

> On 2025-08-08 00:53, Thomas Wolff via Cygwin wrote:
> > Am 08.08.2025 um 02:31 schrieb Jeremy Drake via Cygwin:
> >> On a case-insensitive but case-preserving filesystem, is there a Cygwin
> >> API to get the on-disk case for a given path?  It seems like `realpath`
> >> ought to do it but running
> >> $ touch case-test
> >> $ realpath CASE-TEST
> >> returns CASE-TEST.
> > On the command line, you could use
> > ls | grep -i
> >
> >> Regardless, canonicalize_file_name or realpath may not
> >> be what I want because it would dereference symlinks.
> >>
> >> Background: I'm trying to debug some test failures in Clang, due to a
> >> warning that's supposed to be issued when you #include "foo.h" but the
> >> file on disk that it opened is "Foo.h".
>
> Looks like if you use wildcards, it should work correctly:
>
> $ lsattr -dl .
> .                            ---
> $ l *_exit*
> _Exit.2  _exit.3
> $ l _exit.?
> _Exit.2  _exit.3
> $ l _exit.[23]
> _Exit.2  _exit.3
> $ l *EXIT-TEST*
> exit-test
> $ l *exit*
> _Exit.2  _exit.3  EXIT  exit-test
>
> also, you could just opendir(3)/readdir(3)/closedir(3) and strcasecmp(3).
>

Yeah, globbing is opendir/readdir/closedir, but it'd have to be done on
each path component to recover the on-disk case for a path.  I'll explain
now that I have a better idea what clang is doing under the hood.

llvm has an API that opens a file with an out parameter for the "real"
path.  On Windows, it uses GetFinalPathNameByHandleW
(FILE_NAME_NORMALIZED|VOLUME_NAME_DOS), with some massaging for UNC.  On
Unix, it first would prefer fcntl with F_GETPATH.  It doesn't look like
Cygwin provides that.  If that's not available, available, it tries
readlink on /proc/self/fd/%d.  If that's not available, it falls back to
realpath on the name input.  I had a breakpoint on realpath that was not
hit, so it appears that readlink is what it's doing.

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple