GNU bug report logs - #36405
26.2.90; O_PATH problem on some versions of Cygwin

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Ken Brown <kbrown <at> cornell.edu>
To: "bug-gnu-emacs <at> gnu.org" <bug-gnu-emacs <at> gnu.org>
Subject: 26.2.90; O_PATH problem on some versions of Cygwin
Date: Thu, 27 Jun 2019 19:28:48 +0000

[Message part 1 (text/plain, inline)]

Cygwin supports the O_PATH flag starting with release 3.0.0, but it is buggy 
until release 3.0.8.  (Opening a FIFO with O_PATH causes a hang.)  The attached 
patches work around this problem.  The first patch (which still has a bug number 
that needs to be filled in) uses incorrect indentation for legibility.  The 
second patch fixes the indentation.

Ken

[0001-Avoid-O_PATH-on-versions-of-Cygwin-where-it-is-buggy.patch (text/plain, attachment)]

[0002-src-dired.c-file_attributes-Fix-indentation.patch (text/plain, attachment)]

Message #10 received at 36405-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Ken Brown <kbrown <at> cornell.edu>
Cc: 36405-done <at> debbugs.gnu.org
Subject: Re: 26.2.90; O_PATH problem on some versions of Cygwin
Date: Thu, 27 Jun 2019 13:47:27 -0700

[Message part 1 (text/plain, inline)]

Thanks, but that patch intrudes on the mainline code a bit. It's simpler 
to just disable O_PATH on Cygwin until the old Cygwin versions die out. 
Also, there's a similar issue in fileio.c. I installed the attached, 
which should work around the problem in both source files.

[0001-Work-around-Cygwin-bug-with-O_PATH.patch (text/x-patch, attachment)]

Message #13 received at 36405 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 36405 <at> debbugs.gnu.org, kbrown <at> cornell.edu, eggert <at> cs.ucla.edu
Subject: Re: bug#36405: 26.2.90; O_PATH problem on some versions of Cygwin
Date: Fri, 28 Jun 2019 09:25:02 +0300

> From: Paul Eggert <eggert <at> cs.ucla.edu>
> Date: Thu, 27 Jun 2019 13:47:27 -0700
> Cc: 36405-done <at> debbugs.gnu.org
> 
> Thanks, but that patch intrudes on the mainline code a bit. It's simpler 
> to just disable O_PATH on Cygwin until the old Cygwin versions die out. 

IMO, that's too drastic.  Cygwin 3 is quite new, AFAIK, so it will be
years and years before the old versions die out; no one will remember
this bit by then.

What problems did you see/envision on other platforms with the
original patch?

Message #16 received at 36405 <at> debbugs.gnu.org (full text, mbox):

From: Ken Brown <kbrown <at> cornell.edu>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: Eli Zaretskii <eliz <at> gnu.org>,
 "36405 <at> debbugs.gnu.org" <36405 <at> debbugs.gnu.org>
Subject: Re: 26.2.90; O_PATH problem on some versions of Cygwin
Date: Fri, 28 Jun 2019 17:57:04 +0000

On 6/27/2019 4:47 PM, Paul Eggert wrote:
> --- a/src/fileio.c
> +++ b/src/fileio.c
> @@ -61,6 +61,10 @@ Copyright (C) 1985-1988, 1993-2019 Free Software Foundation, Inc.
>   # include <linux/fs.h>
>   #endif
>   
> +#ifdef __CYGWIN__
> +# undef O_PATH /* Buggy in Cygwin 3.0.0 through 3.0.7.  */
> +#endif

This hunk is not necessary.  The only use of O_PATH in fileio.c is coupled with 
O_DIRECTORY, and this is not affected by the bug.

But, in any case, I agree with Eli's point that your patch is too drastic.  I 
don't see how my patch is intrusive.

Ken

Message #19 received at 36405 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Ken Brown <kbrown <at> cornell.edu>
Cc: Eli Zaretskii <eliz <at> gnu.org>,
 "36405 <at> debbugs.gnu.org" <36405 <at> debbugs.gnu.org>
Subject: Re: 26.2.90; O_PATH problem on some versions of Cygwin
Date: Fri, 28 Jun 2019 23:20:54 -0700

Ken Brown wrote:
> This hunk is not necessary.  The only use of O_PATH in fileio.c is coupled with
> O_DIRECTORY, and this is not affected by the bug.

Thanks, I reverted that part of the change. I'll also follow up to Eli's note.

Message #22 received at 36405 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 36405 <at> debbugs.gnu.org, kbrown <at> cornell.edu
Subject: Re: bug#36405: 26.2.90; O_PATH problem on some versions of Cygwin
Date: Fri, 28 Jun 2019 23:26:09 -0700

[Message part 1 (text/plain, inline)]

Eli Zaretskii wrote:
> What problems did you see/envision on other platforms with the
> original patch?

Mainly the hassle of maintaining code with a lot of hard-to-read ifdefs in it. 
It's better if system-specific stuff is kept to a minimum in mainline code. 
Also, this O_PATH stuff is not that high of a priority, as the code works quite 
well in practice without O_PATH. (Also, if Cygwin botched O_PATH on FIFOs 
there's a reasonable chance it botched O_PATH elsewhere too. :-)

How about something like the attached patch instead? It's simpler and should be 
a bit faster on Cygwin than the original patch. I haven't tested it.

[cygwin.diff (text/x-patch, attachment)]

Message #25 received at 36405 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 36405 <at> debbugs.gnu.org, kbrown <at> cornell.edu
Subject: Re: bug#36405: 26.2.90; O_PATH problem on some versions of Cygwin
Date: Sat, 29 Jun 2019 10:06:49 +0300

> Cc: 36405 <at> debbugs.gnu.org, kbrown <at> cornell.edu
> From: Paul Eggert <eggert <at> cs.ucla.edu>
> Date: Fri, 28 Jun 2019 23:26:09 -0700
> 
> Eli Zaretskii wrote:
> > What problems did you see/envision on other platforms with the
> > original patch?
> 
> Mainly the hassle of maintaining code with a lot of hard-to-read ifdefs in it. 
> It's better if system-specific stuff is kept to a minimum in mainline code. 

I agree, of course.  But in this case we are talking about adding 2
#ifdef's, so the situation is not much worse than it was before.

> Also, this O_PATH stuff is not that high of a priority, as the code works quite 
> well in practice without O_PATH.

It was evidently important enough for us to use it on platforms that
support it.

> How about something like the attached patch instead? It's simpler and should be 
> a bit faster on Cygwin than the original patch. I haven't tested it.

Thanks, this is fine with me if it does the job.  Ken?

Message #28 received at 36405 <at> debbugs.gnu.org (full text, mbox):

From: Ken Brown <kbrown <at> cornell.edu>
To: Eli Zaretskii <eliz <at> gnu.org>, Paul Eggert <eggert <at> cs.ucla.edu>
Cc: "36405 <at> debbugs.gnu.org" <36405 <at> debbugs.gnu.org>
Subject: Re: bug#36405: 26.2.90; O_PATH problem on some versions of Cygwin
Date: Sat, 29 Jun 2019 18:03:02 +0000

[Message part 1 (text/plain, inline)]

On 6/29/2019 3:06 AM, Eli Zaretskii wrote:
>> Cc: 36405 <at> debbugs.gnu.org, kbrown <at> cornell.edu
>> From: Paul Eggert <eggert <at> cs.ucla.edu>
>> Date: Fri, 28 Jun 2019 23:26:09 -0700
>>
>> Eli Zaretskii wrote:
>>> What problems did you see/envision on other platforms with the
>>> original patch?
>>
>> Mainly the hassle of maintaining code with a lot of hard-to-read ifdefs in it.
>> It's better if system-specific stuff is kept to a minimum in mainline code.
> 
> I agree, of course.  But in this case we are talking about adding 2
> #ifdef's, so the situation is not much worse than it was before.
> 
>> Also, this O_PATH stuff is not that high of a priority, as the code works quite
>> well in practice without O_PATH.
> 
> It was evidently important enough for us to use it on platforms that
> support it.
> 
>> How about something like the attached patch instead? It's simpler and should be
>> a bit faster on Cygwin than the original patch. I haven't tested it.
> 
> Thanks, this is fine with me if it does the job.  Ken?

Fine with me too, after a small tweak.  Revised patch attached.

Thanks, Paul.

Ken

[cygwin1.diff (text/plain, attachment)]

Message #31 received at 36405 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Ken Brown <kbrown <at> cornell.edu>
Cc: eggert <at> cs.ucla.edu, 36405 <at> debbugs.gnu.org
Subject: Re: bug#36405: 26.2.90; O_PATH problem on some versions of Cygwin
Date: Sat, 29 Jun 2019 21:19:11 +0300

> From: Ken Brown <kbrown <at> cornell.edu>
> CC: "36405 <at> debbugs.gnu.org" <36405 <at> debbugs.gnu.org>
> Date: Sat, 29 Jun 2019 18:03:02 +0000
> 
> > Thanks, this is fine with me if it does the job.  Ken?
> 
> Fine with me too, after a small tweak.  Revised patch attached.

Go ahead and push, then.

Thanks.

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