From: Zack Weinberg <zackw@panix.com>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: "Arsen Arsenović" <arsen@aarsen.me>,
"GNU C Library" <libc-alpha@sourceware.org>
Subject: Re: [PATCH v2] Ensure standard file descriptors are open on start
Date: Thu, 27 Aug 2020 11:56:47 -0400 [thread overview]
Message-ID: <CAKCAbMiGeimxoMQGdq5BRpkD7QOj8njcNM6g2FDGAv_dLffYDw@mail.gmail.com> (raw)
In-Reply-To: <e9402d52-f83c-b33d-120d-349214df7293@cs.ucla.edu>
On Thu, Aug 20, 2020 at 6:00 PM Paul Eggert <eggert@cs.ucla.edu> wrote:
> Arsen Arsenović wrote:
> > And considering the hint, and that the edge case of stdin being closed
> > seems to have been missed even by the autotools developers (I noticed this
> > when running autoconf-1.64s ./configure from an automation tool that closed
> > fd 0)
>
> If Autoconf doesn't operate well when file descriptor 0 is closed then it
> might be worth changing Autoconf, if it's not too much trouble.
I looked into making that change. However, it is very difficult to
detect and handle closed fds 0,1,2 reliably in a shell script. In C
it's easy (just call fcntl([012], F_GETFL, 0)) but shell programs
cannot make that system call directly, and all of the alternatives
have significant limitations (e.g. not being able to tell whether a fd
is open for *writing*), run foul of bugs (e.g. `exec 3>&0` will
succeed with Solaris /bin/sh, regardless of whether fd 0 was open), or
are not portable enough to use as the sole method (e.g. Linux's
/proc/<pid>/fdinfo/<fd> virtual files). If you're curious what I did,
see https://lists.gnu.org/archive/html/autoconf-patches/2020-08/msg00025.html
and msg00026.html, but right now I am inclined *not* to put those
changes into the upcoming Autoconf 2.70.
After the experience of writing those patches, I'm definitely in favor
of GNU libc making a guarantee that fds 0,1,2 are open when
application code starts executing, for all processes, regardless of
what POSIX does or does not say.
zw
next prev parent reply other threads:[~2020-08-27 15:57 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-19 12:41 Arsen Arsenović
2020-08-19 16:28 ` Joseph Myers
2020-08-19 17:46 ` Zack Weinberg
2020-08-19 17:50 ` Joseph Myers
2020-08-19 18:20 ` Adhemerval Zanella
2020-08-19 19:13 ` Florian Weimer
2020-08-19 19:25 ` Adhemerval Zanella
2020-08-19 19:27 ` Florian Weimer
2020-08-19 19:35 ` Adhemerval Zanella
2020-08-19 19:40 ` Arsen Arsenović
2020-08-19 21:04 ` Michael Morrell
2020-08-19 22:32 ` Joseph Myers
2020-08-19 23:45 ` Arsen Arsenović
2020-08-20 22:00 ` Paul Eggert
2020-08-20 23:25 ` Arsen Arsenović
2020-08-27 15:56 ` Zack Weinberg [this message]
2020-08-27 18:21 ` Paul Eggert
2020-08-28 0:12 ` Arsen Arsenović
2020-09-04 17:49 ` Arsen Arsenović
2020-09-11 7:47 ` ping^2 " Arsen Arsenović
2020-08-19 23:16 ` Rich Felker
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