GNU bug report logs - #56218
[PATCH] guix: inferior: Fix the behaviour of open-inferior #:error-port.

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Christopher Baines <mail <at> cbaines.net>
Subject: bug#56218: closed (Re: bug#56218: [PATCH] guix: inferior: Fix the
 behaviour of open-inferior #:error-port.)
Date: Fri, 08 Jul 2022 12:58:02 +0000

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Your bug report

#56218: [PATCH] guix: inferior: Fix the behaviour of open-inferior #:error-port.

which was filed against the guix-patches package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 56218 <at> debbugs.gnu.org.

-- 
56218: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=56218
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Christopher Baines <mail <at> cbaines.net>
To: Ludovic Courtès <ludo <at> gnu.org>
Cc: 56218-done <at> debbugs.gnu.org
Subject: Re: bug#56218: [PATCH] guix: inferior: Fix the behaviour of
 open-inferior #:error-port.
Date: Fri, 08 Jul 2022 13:54:24 +0100

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Ludovic Courtès <ludo <at> gnu.org> writes:

>>>> +            (dup2 (if (file-port? (current-error-port))
>>>> +                      (fileno (current-error-port))
>>>> +                      (open-fdes "/dev/null" O_WRONLY))
>>>> +                  2)
>>>
>>> If (current-error-port) wraps FD 2 when the function is called, then, by
>>> the time we reach (dup2 … 2), the FD behind (current-error-port) has be
>>> closed; we end up doing (dup2 2 2), but FD 2 is closed, so we get EBADF.
>>>
>>> Or am I misunderstanding?
>>
>> That sounds reasonable, I've only tested this change in the scenario
>> when the #:error-port isn't stderr, and I mostly adapted this from what
>> I thought open-pipe* did.
>>
>> Maxime suggested using move->fdes, so maybe this would be an improved
>> version:
>>
>>   ;; Mimic 'open-pipe*'.
>>   (if (file-port? (current-error-port))
>>       (unless (eq? (fileno (current-error-port)) 2)
>>         (move-fdes (current-error-port) 2))
>>       (move->fdes (open-file "/dev/null" O_WRONLY) 2))
>
> I prefer the original version: I find it clearer (it’s low-level) and
> probably more robust (thinking through the port/FD interaction needs is
> more demanding :-)).
>
>>> Perhaps we should add one test for each case (error port is a file port
>>> vs. error port is another kind of port) in ‘tests/inferior.scm’.
>>
>> Yep, sounds good.
>
> To sum up: I think it’s a welcome change, and it’s even more welcome
> with a couple of tests to make sure it behaves the way we think it does.

I've gone ahead and pushed a fix plus some tests as
a9fd06121240c78071a398dd1e0ddb47553f3809.

The tests probably aren't great, but I think the do cover the
#:error-port behaviour.

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From: Christopher Baines <mail <at> cbaines.net>
To: guix-patches <at> gnu.org
Subject: [PATCH] guix: inferior: Fix the behaviour of open-inferior
 #:error-port.
Date: Sat, 25 Jun 2022 18:18:47 +0100

This should be the error port used by the inferior process, but currently it's
either stderr if #:error-port is a file port, or /dev/null otherwise.

I'm looking at this as the Guix Data Service uses this behaviour to record and
display logs from inferior processes.

* guix/inferior.scm (open-bidirectional-pipe): Call dup2 for file descriptor
2, passing either the file number for the current error port, or a file
descriptor for /dev/null.
---
 guix/inferior.scm | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/guix/inferior.scm b/guix/inferior.scm
index 54200b75e4..e36806ac84 100644
--- a/guix/inferior.scm
+++ b/guix/inferior.scm
@@ -156,12 +156,14 @@ (define (open-bidirectional-pipe command . args)
             (close-port parent)
             (close-fdes 0)
             (close-fdes 1)
+            (close-fdes 2)
             (dup2 (fileno child) 0)
             (dup2 (fileno child) 1)
             ;; Mimic 'open-pipe*'.
-            (unless (file-port? (current-error-port))
-              (close-fdes 2)
-              (dup2 (open-fdes "/dev/null" O_WRONLY) 2))
+            (dup2 (if (file-port? (current-error-port))
+                      (fileno (current-error-port))
+                      (open-fdes "/dev/null" O_WRONLY))
+                  2)
             (apply execlp command command args))
           (lambda ()
             (primitive-_exit 127))))
-- 
2.36.1

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