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From: "cquike at arcor dot de" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug libc/29147] New: Wrong values for symbolic constants defined in
 limits.h
Date: Sat, 14 May 2022 23:05:24 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D29147

            Bug ID: 29147
           Summary: Wrong values for symbolic constants defined in
                    limits.h
           Product: glibc
           Version: 2.34
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: cquike at arcor dot de
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Created attachment 14102
  --> https://sourceware.org/bugzilla/attachment.cgi?id=3D14102&action=3Ded=
it
Potential patch

I am trying to understand the output of some of the values in getconf and I
came to the conclusion that a number of symbolic constants defined in limit=
s.h
are not properly printed by getconf utility.

According to POSIX.1-2018
(https://pubs.opengroup.org/onlinepubs/9699919799/utilities/getconf.html), =
the
getconf utility shall print "the symbolic constants listed under the headin=
gs
``Maximum Values'' and ``Minimum Values'' in the description of the <limits=
.h>
header". Quoting the reference book "Advanced Programming in the UNIX
environment": "Those minimum values do not change from one system to anothe=
r.
They specify the most restrictive values for these features".

I realized first with the _POSIX_PIPE_BUF constant. According to POSIX.1-20=
18
(https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html) t=
he
value must be 512. However, on a Fedora 35 machine:

# getconf -a | grep  _POSIX_PIPE_BUF
_POSIX_PIPE_BUF                    4096

Looking at the sources it seems that _POSIX_PIPE_BUF (the minimum value for
_any_ POSIX implementation) is using pathconf(_PC_PIPE_BUF, ...) which is t=
he
value for _this_ specific implementation.

I have jot down a potential patch that fixes the problem (albeit only for
_POSIX_PIPE_BUF, not for the rest of the constants in limits.h) and have
attached it here.

--=20
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