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annotate lib/cycle-check.c @ 7292:17785d5bede0

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Fix docstrings
author Sergey Poznyakoff <gray@gnu.org.ua>
date Sun, 10 Sep 2006 11:52:44 +0000
parents 314715e0260d
children 8a1a9361108c
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1 /* help detect directory cycles efficiently
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2
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3 Copyright (C) 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
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4
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5 This program is free software; you can redistribute it and/or modify
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6 it under the terms of the GNU General Public License as published by
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7 the Free Software Foundation; either version 2, or (at your option)
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8 any later version.
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9
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10 This program is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU General Public License for more details.
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14
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15 You should have received a copy of the GNU General Public License
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16 along with this program; see the file COPYING.
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17 If not, write to the Free Software Foundation,
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18 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
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19
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20 /* Written by Jim Meyering */
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21
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22 #ifdef HAVE_CONFIG_H
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23 # include <config.h>
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24 #endif
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25
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26 #include <sys/types.h>
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27 #include <sys/stat.h>
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28 #include <stdio.h>
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29 #include <assert.h>
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30 #include <stdlib.h>
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31
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32 #include <stdbool.h>
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33
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34 #include "cycle-check.h"
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35
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36 #define CC_MAGIC 9827862
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37
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38 /* Return true if I is a power of 2, or is zero. */
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39
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40 static inline bool
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41 is_zero_or_power_of_two (uintmax_t i)
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42 {
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43 return (i & (i - 1)) == 0;
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44 }
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45
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46 void
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47 cycle_check_init (struct cycle_check_state *state)
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48 {
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49 state->chdir_counter = 0;
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50 state->magic = CC_MAGIC;
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51 }
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52
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53 /* In traversing a directory hierarchy, call this function once for each
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54 descending chdir call, with SB corresponding to the chdir operand.
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55 If SB corresponds to a directory that has already been seen,
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56 return true to indicate that there is a directory cycle.
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57 Note that this is done `lazily', which means that some of
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58 the directories in the cycle may be processed twice before
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59 the cycle is detected. */
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60
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61 bool
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62 cycle_check (struct cycle_check_state *state, struct stat const *sb)
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63 {
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64 assert (state->magic == CC_MAGIC);
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65
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66 /* If the current directory ever happens to be the same
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67 as the one we last recorded for the cycle detection,
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68 then it's obviously part of a cycle. */
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69 if (state->chdir_counter && SAME_INODE (*sb, state->dev_ino))
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70 return true;
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71
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72 /* If the number of `descending' chdir calls is a power of two,
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73 record the dev/ino of the current directory. */
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74 if (is_zero_or_power_of_two (++(state->chdir_counter)))
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75 {
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76 /* On all architectures that we know about, if the counter
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77 overflows then there is a directory cycle here somewhere,
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78 even if we haven't detected it yet. Typically this happens
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79 only after the counter is incremented 2**64 times, so it's a
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80 fairly theoretical point. */
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81 if (state->chdir_counter == 0)
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82 return true;
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83
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84 state->dev_ino.st_dev = sb->st_dev;
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85 state->dev_ino.st_ino = sb->st_ino;
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86 }
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87
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88 return false;
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89 }