| xf.li | bdd93d5 | 2023-05-12 07:10:14 -0700 | [diff] [blame^] | 1 | /* Threshold at which to diagnose ELOOP. Generic version. |
| 2 | Copyright (C) 2012-2016 Free Software Foundation, Inc. |
| 3 | This file is part of the GNU C Library. |
| 4 | |
| 5 | The GNU C Library is free software; you can redistribute it and/or |
| 6 | modify it under the terms of the GNU Lesser General Public |
| 7 | License as published by the Free Software Foundation; either |
| 8 | version 2.1 of the License, or (at your option) any later version. |
| 9 | |
| 10 | The GNU C Library is distributed in the hope that it will be useful, |
| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 13 | Lesser General Public License for more details. |
| 14 | |
| 15 | You should have received a copy of the GNU Lesser General Public |
| 16 | License along with the GNU C Library; if not, see |
| 17 | <http://www.gnu.org/licenses/>. */ |
| 18 | |
| 19 | #ifndef _ELOOP_THRESHOLD_H |
| 20 | #define _ELOOP_THRESHOLD_H 1 |
| 21 | |
| 22 | #include <limits.h> |
| 23 | #include <sys/param.h> |
| 24 | |
| 25 | /* POSIX specifies SYMLOOP_MAX as the "Maximum number of symbolic |
| 26 | links that can be reliably traversed in the resolution of a |
| 27 | pathname in the absence of a loop." This makes it a minimum that |
| 28 | we should certainly accept. But it leaves open the possibility |
| 29 | that more might sometimes work--just not "reliably". |
| 30 | |
| 31 | For example, Linux implements a complex policy whereby there is a |
| 32 | small limit on the number of direct symlink traversals (a symlink |
| 33 | to a symlink to a symlink), but larger limit on the total number of |
| 34 | symlink traversals overall. Hence the SYMLOOP_MAX number should be |
| 35 | the small one, but the limit library functions enforce on users |
| 36 | should be the larger one. |
| 37 | |
| 38 | So, we use the larger of the reported SYMLOOP_MAX (if any) and our |
| 39 | own constant MIN_ELOOP_THRESHOLD, below. This constant should be |
| 40 | large enough that it never rules out a file name and directory tree |
| 41 | that the underlying system (i.e. calls to 'open' et al) would |
| 42 | resolve successfully. It should be small enough that actual loops |
| 43 | are detected without a huge number of iterations. */ |
| 44 | |
| 45 | #ifndef MIN_ELOOP_THRESHOLD |
| 46 | # define MIN_ELOOP_THRESHOLD 40 |
| 47 | #endif |
| 48 | |
| 49 | /* Return the maximum number of symlink traversals to permit |
| 50 | before diagnosing ELOOP. */ |
| 51 | static inline unsigned int __attribute__ ((const)) |
| 52 | __eloop_threshold (void) |
| 53 | { |
| 54 | #ifdef SYMLOOP_MAX |
| 55 | const int symloop_max = SYMLOOP_MAX; |
| 56 | #else |
| 57 | /* The function is marked 'const' even though we use memory and |
| 58 | call a function, because sysconf is required to return the |
| 59 | same value in every call and so it must always be safe to |
| 60 | call __eloop_threshold exactly once and reuse the value. */ |
| 61 | static long int sysconf_symloop_max; |
| 62 | if (sysconf_symloop_max == 0) |
| 63 | sysconf_symloop_max = __sysconf (_SC_SYMLOOP_MAX); |
| 64 | const unsigned int symloop_max = (sysconf_symloop_max <= 0 |
| 65 | ? _POSIX_SYMLOOP_MAX |
| 66 | : sysconf_symloop_max); |
| 67 | #endif |
| 68 | |
| 69 | return MAX (symloop_max, MIN_ELOOP_THRESHOLD); |
| 70 | } |
| 71 | |
| 72 | #endif /* eloop-threshold.h */ |