mirror of
https://github.com/coreutils/coreutils.git
synced 2024-12-18 14:27:41 +08:00
94 lines
2.8 KiB
C
94 lines
2.8 KiB
C
/* 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;
|
|
}
|