lib/same.c

   1 /* Determine whether two file names refer to the same file.
   2
   3    Copyright (C) 1997-2000, 2002-2006, 2009-2025 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 <fcntl.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 /* Whether file name components are silently truncated (behavior that
  48    POSIX stopped allowing in 2008).  This enables checks whether
  49    truncated base names are the same, while checking the directories.  */
  50 #if !_POSIX_NO_TRUNC && HAVE_FPATHCONF && defined _PC_NAME_MAX
  51 # define CHECK_TRUNCATION true
  52 #else
  53 # define CHECK_TRUNCATION false
  54 #endif
  55
  56 /* Return nonzero if SOURCE and DEST point to the same name in the same
  57    directory.  */
  58
  59 bool
  60 same_name (const char *source, const char *dest)
  61 {
  62   return same_nameat (AT_FDCWD, source, AT_FDCWD, dest);
  63 }
  64
  65 /* Likewise, but interpret the file names relative to SOURCE_FD and DEST_FD,
  66    in the style of openat.  */
  67
  68 bool
  69 same_nameat (int source_dfd, char const *source,
  70              int dest_dfd, char const *dest)
  71 {
  72   /* Compare the basenames.  */
  73   char const *source_basename = last_component (source);
  74   char const *dest_basename = last_component (dest);
  75   size_t source_baselen = base_len (source_basename);
  76   size_t dest_baselen = base_len (dest_basename);
  77   bool identical_basenames =
  78     (source_baselen == dest_baselen
  79      && memcmp (source_basename, dest_basename, dest_baselen) == 0);
  80   bool compare_dirs = identical_basenames;
  81   bool same = false;
  82
  83 #if CHECK_TRUNCATION
  84   size_t slen_max = HAVE_LONG_FILE_NAMES ? 255 : _POSIX_NAME_MAX;
  85   size_t min_baselen = MIN (source_baselen, dest_baselen);
  86   if (slen_max <= min_baselen
  87       && memcmp (source_basename, dest_basename, slen_max) == 0)
  88     compare_dirs = true;
  89 #endif
  90
  91   if (compare_dirs)
  92     {
  93       struct stat source_dir_stats;
  94       struct stat dest_dir_stats;
  95
  96       /* Compare the parent directories (via the device and inode numbers).  */
  97       char *source_dirname = dir_name (source);
  98       int flags = AT_SYMLINK_NOFOLLOW;
  99       if (fstatat (source_dfd, source_dirname, &source_dir_stats, flags) != 0)
 100         {
 101           /* Shouldn't happen.  */
 102           error (1, errno, "%s", source_dirname);
 103         }
 104       free (source_dirname);
 105
 106       char *dest_dirname = dir_name (dest);
 107
 108 #if CHECK_TRUNCATION
 109       int destdir_errno = 0;
 110       int open_flags = O_SEARCH | O_CLOEXEC | O_DIRECTORY;
 111       int destdir_fd = openat (dest_dfd, dest_dirname, open_flags);
 112       if (destdir_fd < 0 || fstat (destdir_fd, &dest_dir_stats) != 0)
 113         destdir_errno = errno;
 114       else if (psame_inode (&source_dir_stats, &dest_dir_stats))
 115         {
 116           same = identical_basenames;
 117           if (! same)
 118             {
 119               errno = 0;
 120               long name_max = fpathconf (destdir_fd, _PC_NAME_MAX);
 121               if (name_max < 0)
 122                 destdir_errno = errno;
 123               else
 124                 same = (name_max <= min_baselen
 125                         && (memcmp (source_basename, dest_basename, name_max)
 126                             == 0));
 127             }
 128         }
 129       close (destdir_fd);
 130       if (destdir_errno != 0)
 131         {
 132           /* Shouldn't happen.  */
 133           error (1, destdir_errno, "%s", dest_dirname);
 134         }
 135 #else
 136       if (fstatat (dest_dfd, dest_dirname, &dest_dir_stats, flags) != 0)
 137         {
 138           /* Shouldn't happen.  */
 139           error (1, errno, "%s", dest_dirname);
 140         }
 141       same = psame_inode (&source_dir_stats, &dest_dir_stats);
 142 #endif
 143
 144       free (dest_dirname);
 145     }
 146
 147   return same;
 148 }