/* help detect directory cycles efficiently Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. This program 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 General Public License for more details. You should have received a copy of the GNU General Public License along with this program; see the file COPYING. If not, write to the Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ /* Written by Jim Meyering */ #ifdef HAVE_CONFIG_H # include <config.h> #endif #include <sys/types.h> #include <sys/stat.h> #include <stdio.h> #include <assert.h> #include <stdlib.h> #include <stdbool.h> #include "cycle-check.h" #define SAME_INODE(Stat_buf_1, Stat_buf_2) \ ((Stat_buf_1).st_ino == (Stat_buf_2).st_ino \ && (Stat_buf_1).st_dev == (Stat_buf_2).st_dev) #define CC_MAGIC 9827862 /* Return true if I is a power of 2, or is zero. */ static inline bool is_zero_or_power_of_two (uintmax_t i) { return (i & (i - 1)) == 0; } void cycle_check_init (struct cycle_check_state *state) { state->chdir_counter = 0; state->magic = CC_MAGIC; } /* In traversing a directory hierarchy, call this function once for each descending chdir call, with SB corresponding to the chdir operand. If SB corresponds to a directory that has already been seen, return true to indicate that there is a directory cycle. Note that this is done `lazily', which means that some of the directories in the cycle may be processed twice before the cycle is detected. */ bool cycle_check (struct cycle_check_state *state, struct stat const *sb) { assert (state->magic == CC_MAGIC); /* If the current directory ever happens to be the same as the one we last recorded for the cycle detection, then it's obviously part of a cycle. */ if (state->chdir_counter && SAME_INODE (*sb, state->dev_ino)) return true; /* If the number of `descending' chdir calls is a power of two, record the dev/ino of the current directory. */ if (is_zero_or_power_of_two (++(state->chdir_counter))) { /* On all architectures that we know about, if the counter overflows then there is a directory cycle here somewhere, even if we haven't detected it yet. Typically this happens only after the counter is incremented 2**64 times, so it's a fairly theoretical point. */ if (state->chdir_counter == 0) return true; state->dev_ino.st_dev = sb->st_dev; state->dev_ino.st_ino = sb->st_ino; } return false; }