New cycle-check module imported from coreutils.

diff --git a/lib/cycle-check.c b/lib/cycle-check.c
new file mode 100644 (file)
index 0000000..99a88c3
--- /dev/null
+++ b/lib/cycle-check.c
@@ -0,0 +1,94 @@
+/* help detect directory cycles efficiently
+
+   Copyright (C) 2003, 2004 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,
+   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+
+/* Written by Jim Meyering */
+
+#if 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"
+#include "xalloc.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;
+}

diff --git a/lib/cycle-check.h b/lib/cycle-check.h
new file mode 100644 (file)
index 0000000..7b7f54d
--- /dev/null
+++ b/lib/cycle-check.h
@@ -0,0 +1,44 @@
+/* help detect directory cycles efficiently
+
+   Copyright (C) 2003, 2004 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,
+   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+
+/* Written by Jim Meyering */
+
+#ifndef CYCLE_CHECK_H
+# define CYCLE_CHECK_H 1
+
+# if HAVE_INTTYPES_H
+#  include <inttypes.h>
+# endif
+# if HAVE_STDINT_H
+#  include <stdint.h>
+# endif
+# include <stdbool.h>
+# include "dev-ino.h"
+
+struct cycle_check_state
+{
+  struct dev_ino dev_ino;
+  uintmax_t chdir_counter;
+  int magic;
+};
+
+void cycle_check_init (struct cycle_check_state *state);
+bool cycle_check (struct cycle_check_state *state, struct stat const *sb);
+
+#endif

diff --git a/lib/dev-ino.h b/lib/dev-ino.h
new file mode 100644 (file)
index 0000000..695d38c
--- /dev/null
+++ b/lib/dev-ino.h
@@ -0,0 +1,13 @@
+#ifndef DEV_INO_H
+# define DEV_INO_H 1
+
+# include <sys/types.h>
+# include <sys/stat.h>
+
+struct dev_ino
+{
+  ino_t st_ino;
+  dev_t st_dev;
+};
+
+#endif

diff --git a/modules/cycle-check b/modules/cycle-check
new file mode 100644 (file)
index 0000000..91c4e31
--- /dev/null
+++ b/modules/cycle-check
@@ -0,0 +1,21 @@
+Description:
+help detect directory cycles efficiently
+
+Files:
+lib/cycle-check.c
+lib/cycle-check.h
+lib/dev-ino.h
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+lib_SOURCES += cycle-check.c cycle-check.h dev-ino.h
+
+Include:
+"cycle-check.h"
+
+Maintainer:
+Jim Meyering
+