From 4f75b7a09a57e0d33ee0741c18114ce8ac5d6c3f Mon Sep 17 00:00:00 2001 From: Roland McGrath Date: Wed, 1 Aug 2012 10:33:11 -0700 Subject: Distinguish ELOOP diagnosis threshold from SYMLOOP_MAX. --- sysdeps/generic/eloop-threshold.h | 72 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 72 insertions(+) create mode 100644 sysdeps/generic/eloop-threshold.h (limited to 'sysdeps/generic/eloop-threshold.h') diff --git a/sysdeps/generic/eloop-threshold.h b/sysdeps/generic/eloop-threshold.h new file mode 100644 index 0000000000..2342d29a23 --- /dev/null +++ b/sysdeps/generic/eloop-threshold.h @@ -0,0 +1,72 @@ +/* Threshold at which to diagnose ELOOP. Generic version. + Copyright (C) 2012 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#ifndef _ELOOP_THRESHOLD_H +#define _ELOOP_THRESHOLD_H 1 + +#include +#include + +/* POSIX specifies SYMLOOP_MAX as the "Maximum number of symbolic + links that can be reliably traversed in the resolution of a + pathname in the absence of a loop." This makes it a minimum that + we should certainly accept. But it leaves open the possibility + that more might sometimes work--just not "reliably". + + For example, Linux implements a complex policy whereby there is a + small limit on the number of direct symlink traversals (a symlink + to a symlink to a symlink), but larger limit on the total number of + symlink traversals overall. Hence the SYMLOOP_MAX number should be + the small one, but the limit library functions enforce on users + should be the larger one. + + So, we use the larger of the reported SYMLOOP_MAX (if any) and our + own constant MIN_ELOOP_THRESHOLD, below. This constant should be + large enough that it never rules out a file name and directory tree + that the underlying system (i.e. calls to 'open' et al) would + resolve successfully. It should be small enough that actual loops + are detected without a huge number of iterations. */ + +#ifndef MIN_ELOOP_THRESHOLD +# define MIN_ELOOP_THRESHOLD 40 +#endif + +/* Return the maximum number of symlink traversals to permit + before diagnosing ELOOP. */ +static inline unsigned int __attribute__ ((const)) +__eloop_threshold (void) +{ +#ifdef SYMLOOP_MAX + const int symloop_max = SYMLOOP_MAX; +#else + /* The function is marked 'const' even though we use memory and + call a function, because sysconf is required to return the + same value in every call and so it must always be safe to + call __eloop_threshold exactly once and reuse the value. */ + static long int sysconf_symloop_max; + if (sysconf_symloop_max == 0) + sysconf_symloop_max = __sysconf (_SC_SYMLOOP_MAX); + const unsigned int symloop_max = (sysconf_symloop_max <= 0 + ? _POSIX_SYMLOOP_MAX + : sysconf_symloop_max); +#endif + + return MAX (symloop_max, MIN_ELOOP_THRESHOLD); +} + +#endif /* eloop-threshold.h */ -- cgit 1.4.1