lib/same.c

   1 /* Determine whether two file names refer to the same file.
   2    Copyright (C) 1997-2000, 2002-2003 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 /* written by Jim Meyering */
  19
  20 #if HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #include <stdbool.h>
  25 #include <stdio.h>
  26 #ifdef HAVE_UNISTD_H
  27 # include <unistd.h>
  28 #endif
  29 #include <stdlib.h>
  30 #include <sys/types.h>
  31 #include <sys/stat.h>
  32 #include <ctype.h>
  33 #include <errno.h>
  34 #ifndef errno
  35 extern int errno;
  36 #endif
  37
  38 #include <string.h>
  39
  40 #include <limits.h>
  41 #ifndef _POSIX_NAME_MAX
  42 # define _POSIX_NAME_MAX 14
  43 #endif
  44
  45 #include "same.h"
  46 #include "dirname.h"
  47 #include "error.h"
  48 #include "xalloc.h"
  49
  50 #define MIN(a, b) ((a) < (b) ? (a) : (b))
  51
  52 #define SAME_INODE(Stat_buf_1, Stat_buf_2) \
  53   ((Stat_buf_1).st_ino == (Stat_buf_2).st_ino \
  54    && (Stat_buf_1).st_dev == (Stat_buf_2).st_dev)
  55
  56 /* Return nonzero if SOURCE and DEST point to the same name in the same
  57    directory.  */
  58
  59 int
  60 same_name (const char *source, const char *dest)
  61 {
  62   /* Compare the basenames.  */
  63   char const *source_basename = base_name (source);
  64   char const *dest_basename = base_name (dest);
  65   size_t source_baselen = base_len (source_basename);
  66   size_t dest_baselen = base_len (dest_basename);
  67   bool identical_basenames =
  68     (source_baselen == dest_baselen
  69      && memcmp (source_basename, dest_basename, dest_baselen) == 0);
  70   bool compare_dirs = identical_basenames;
  71   bool same = false;
  72
  73 #if ! _POSIX_NO_TRUNC && HAVE_PATHCONF && defined _PC_NAME_MAX
  74   /* This implementation silently truncates pathname components.  If
  75      the base names might be truncated, check whether the truncated
  76      base names are the same, while checking the directories.  */
  77   size_t slen_max = HAVE_LONG_FILE_NAMES ? 255 : _POSIX_NAME_MAX;
  78   size_t min_baselen = MIN (source_baselen, dest_baselen);
  79   if (slen_max <= min_baselen
  80       && memcmp (source_basename, dest_basename, slen_max) == 0)
  81     compare_dirs = true;
  82 #endif
  83
  84   if (compare_dirs)
  85     {
  86       struct stat source_dir_stats;
  87       struct stat dest_dir_stats;
  88       char *source_dirname, *dest_dirname;
  89
  90       /* Compare the parent directories (via the device and inode numbers).  */
  91       source_dirname = dir_name (source);
  92       dest_dirname = dir_name (dest);
  93
  94       if (stat (source_dirname, &source_dir_stats))
  95         {
  96           /* Shouldn't happen.  */
  97           error (1, errno, "%s", source_dirname);
  98         }
  99
 100       if (stat (dest_dirname, &dest_dir_stats))
 101         {
 102           /* Shouldn't happen.  */
 103           error (1, errno, "%s", dest_dirname);
 104         }
 105
 106       same = SAME_INODE (source_dir_stats, dest_dir_stats);
 107
 108 #if ! _POSIX_NO_TRUNC && HAVE_PATHCONF && defined _PC_NAME_MAX
 109       if (same && ! identical_basenames)
 110         {
 111           long name_max = (errno = 0, pathconf (dest_dirname, _PC_NAME_MAX));
 112           if (name_max < 0)
 113             {
 114               if (errno)
 115                 {
 116                   /* Shouldn't happen.  */
 117                   error (1, errno, "%s", dest_dirname);
 118                 }
 119               same = false;
 120             }
 121           else
 122             same = (name_max <= min_baselen
 123                     && memcmp (source_basename, dest_basename, name_max) == 0);
 124         }
 125 #endif
 126
 127       free (source_dirname);
 128       free (dest_dirname);
 129     }
 130
 131   return same;
 132 }