summaryrefslogtreecommitdiffstats
path: root/lib/eloop-threshold.h
diff options
context:
space:
mode:
Diffstat (limited to 'lib/eloop-threshold.h')
-rw-r--r--lib/eloop-threshold.h83
1 files changed, 83 insertions, 0 deletions
diff --git a/lib/eloop-threshold.h b/lib/eloop-threshold.h
new file mode 100644
index 0000000..8b31457
--- /dev/null
+++ b/lib/eloop-threshold.h
@@ -0,0 +1,83 @@
+/* Threshold at which to diagnose ELOOP. Generic version.
+ Copyright (C) 2012-2022 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
+ <https://www.gnu.org/licenses/>. */
+
+#ifndef _ELOOP_THRESHOLD_H
+#define _ELOOP_THRESHOLD_H 1
+
+#include <limits.h>
+#ifdef _LIBC
+# include <sys/param.h>
+# define _GL_ATTRIBUTE_CONST __attribute__ ((const))
+#else
+# include <unistd.h>
+# include "minmax.h"
+# define __sysconf sysconf
+# if (!defined SYMLOOP_MAX \
+ && ! (defined _SC_SYMLOOP_MAX && defined _POSIX_SYMLOOP_MAX))
+# define SYMLOOP_MAX 8
+# endif
+#endif
+
+/* 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 _GL_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 */