lib/same.c

   1 /* Determine whether two file names refer to the same file.
   2
   3    Copyright (C) 1997-2000, 2002-2006, 2009-2017 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* written by Jim Meyering */
  19
  20 #include <config.h>
  21
  22 #include <stdbool.h>
  23 #include <stdio.h>
  24 #include <unistd.h>
  25 #include <stdlib.h>
  26 #include <sys/types.h>
  27 #include <sys/stat.h>
  28 #include <ctype.h>
  29 #include <errno.h>
  30
  31 #include <string.h>
  32
  33 #include <limits.h>
  34 #ifndef _POSIX_NAME_MAX
  35 # define _POSIX_NAME_MAX 14
  36 #endif
  37
  38 #include "same.h"
  39 #include "dirname.h"
  40 #include "error.h"
  41 #include "same-inode.h"
  42
  43 #ifndef MIN
  44 # define MIN(a, b) ((a) < (b) ? (a) : (b))
  45 #endif
  46
  47 /* Return nonzero if SOURCE and DEST point to the same name in the same
  48    directory.  */
  49
  50 bool
  51 same_name (const char *source, const char *dest)
  52 {
  53   /* Compare the basenames.  */
  54   char const *source_basename = last_component (source);
  55   char const *dest_basename = last_component (dest);
  56   size_t source_baselen = base_len (source_basename);
  57   size_t dest_baselen = base_len (dest_basename);
  58   bool identical_basenames =
  59     (source_baselen == dest_baselen
  60      && memcmp (source_basename, dest_basename, dest_baselen) == 0);
  61   bool compare_dirs = identical_basenames;
  62   bool same = false;
  63
  64 #if ! _POSIX_NO_TRUNC && HAVE_PATHCONF && defined _PC_NAME_MAX
  65   /* This implementation silently truncates components of file names.  If
  66      the base names might be truncated, check whether the truncated
  67      base names are the same, while checking the directories.  */
  68   size_t slen_max = HAVE_LONG_FILE_NAMES ? 255 : _POSIX_NAME_MAX;
  69   size_t min_baselen = MIN (source_baselen, dest_baselen);
  70   if (slen_max <= min_baselen
  71       && memcmp (source_basename, dest_basename, slen_max) == 0)
  72     compare_dirs = true;
  73 #endif
  74
  75   if (compare_dirs)
  76     {
  77       struct stat source_dir_stats;
  78       struct stat dest_dir_stats;
  79       char *source_dirname, *dest_dirname;
  80
  81       /* Compare the parent directories (via the device and inode numbers).  */
  82       source_dirname = dir_name (source);
  83       dest_dirname = dir_name (dest);
  84
  85       if (stat (source_dirname, &source_dir_stats))
  86         {
  87           /* Shouldn't happen.  */
  88           error (1, errno, "%s", source_dirname);
  89         }
  90
  91       if (stat (dest_dirname, &dest_dir_stats))
  92         {
  93           /* Shouldn't happen.  */
  94           error (1, errno, "%s", dest_dirname);
  95         }
  96
  97       same = SAME_INODE (source_dir_stats, dest_dir_stats);
  98
  99 #if ! _POSIX_NO_TRUNC && HAVE_PATHCONF && defined _PC_NAME_MAX
 100       if (same && ! identical_basenames)
 101         {
 102           long name_max = (errno = 0, pathconf (dest_dirname, _PC_NAME_MAX));
 103           if (name_max < 0)
 104             {
 105               if (errno)
 106                 {
 107                   /* Shouldn't happen.  */
 108                   error (1, errno, "%s", dest_dirname);
 109                 }
 110               same = false;
 111             }
 112           else
 113             same = (name_max <= min_baselen
 114                     && memcmp (source_basename, dest_basename, name_max) == 0);
 115         }
 116 #endif
 117
 118       free (source_dirname);
 119       free (dest_dirname);
 120     }
 121
 122   return same;
 123 }