lib/link.c

   1 /* Emulate link on platforms that lack it, namely native Windows platforms.
   2
   3    Copyright (C) 2009-2020 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 2, or (at your option)
   8    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 #include <config.h>
  19
  20 #include <unistd.h>
  21
  22 #include <errno.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/stat.h>
  26
  27 #if !HAVE_LINK
  28 # if defined _WIN32 && ! defined __CYGWIN__
  29
  30 #  define WIN32_LEAN_AND_MEAN
  31 #  include <windows.h>
  32
  33 /* Don't assume that UNICODE is not defined.  */
  34 #  undef GetModuleHandle
  35 #  define GetModuleHandle GetModuleHandleA
  36 #  undef CreateHardLink
  37 #  define CreateHardLink CreateHardLinkA
  38
  39 #  if !(_WIN32_WINNT >= _WIN32_WINNT_WINXP)
  40
  41 /* Avoid warnings from gcc -Wcast-function-type.  */
  42 #   define GetProcAddress \
  43      (void *) GetProcAddress
  44
  45 /* CreateHardLink was introduced only in Windows 2000.  */
  46 typedef BOOL (WINAPI * CreateHardLinkFuncType) (LPCSTR lpFileName,
  47                                                 LPCSTR lpExistingFileName,
  48                                                 LPSECURITY_ATTRIBUTES lpSecurityAttributes);
  49 static CreateHardLinkFuncType CreateHardLinkFunc = NULL;
  50 static BOOL initialized = FALSE;
  51
  52 static void
  53 initialize (void)
  54 {
  55   HMODULE kernel32 = GetModuleHandle ("kernel32.dll");
  56   if (kernel32 != NULL)
  57     {
  58       CreateHardLinkFunc =
  59         (CreateHardLinkFuncType) GetProcAddress (kernel32, "CreateHardLinkA");
  60     }
  61   initialized = TRUE;
  62 }
  63
  64 #  else
  65
  66 #   define CreateHardLinkFunc CreateHardLink
  67
  68 #  endif
  69
  70 int
  71 link (const char *file1, const char *file2)
  72 {
  73   char *dir;
  74   size_t len1 = strlen (file1);
  75   size_t len2 = strlen (file2);
  76
  77 #  if !(_WIN32_WINNT >= _WIN32_WINNT_WINXP)
  78   if (!initialized)
  79     initialize ();
  80 #  endif
  81
  82   if (CreateHardLinkFunc == NULL)
  83     {
  84       /* System does not support hard links.  */
  85       errno = EPERM;
  86       return -1;
  87     }
  88   /* Reject trailing slashes on non-directories; mingw does not
  89      support hard-linking directories.  */
  90   if ((len1 && (file1[len1 - 1] == '/' || file1[len1 - 1] == '\\'))
  91       || (len2 && (file2[len2 - 1] == '/' || file2[len2 - 1] == '\\')))
  92     {
  93       struct stat st;
  94       if (stat (file1, &st) == 0 && S_ISDIR (st.st_mode))
  95         errno = EPERM;
  96       else
  97         errno = ENOTDIR;
  98       return -1;
  99     }
 100   /* CreateHardLink("b/.","a",NULL) creates file "b", so we must check
 101      that dirname(file2) exists.  */
 102   dir = strdup (file2);
 103   if (!dir)
 104     return -1;
 105   {
 106     struct stat st;
 107     char *p = strchr (dir, '\0');
 108     while (dir < p && (*--p != '/' && *p != '\\'));
 109     *p = '\0';
 110     if (p != dir && stat (dir, &st) != 0 && errno != EOVERFLOW)
 111       {
 112         int saved_errno = errno;
 113         free (dir);
 114         errno = saved_errno;
 115         return -1;
 116       }
 117     free (dir);
 118   }
 119   /* Now create the link.  */
 120   if (CreateHardLinkFunc (file2, file1, NULL) == 0)
 121     {
 122       /* It is not documented which errors CreateHardLink() can produce.
 123        * The following conversions are based on tests on a Windows XP SP2
 124        * system. */
 125       DWORD err = GetLastError ();
 126       switch (err)
 127         {
 128         case ERROR_ACCESS_DENIED:
 129           errno = EACCES;
 130           break;
 131
 132         case ERROR_INVALID_FUNCTION:    /* fs does not support hard links */
 133           errno = EPERM;
 134           break;
 135
 136         case ERROR_NOT_SAME_DEVICE:
 137           errno = EXDEV;
 138           break;
 139
 140         case ERROR_PATH_NOT_FOUND:
 141         case ERROR_FILE_NOT_FOUND:
 142           errno = ENOENT;
 143           break;
 144
 145         case ERROR_INVALID_PARAMETER:
 146           errno = ENAMETOOLONG;
 147           break;
 148
 149         case ERROR_TOO_MANY_LINKS:
 150           errno = EMLINK;
 151           break;
 152
 153         case ERROR_ALREADY_EXISTS:
 154           errno = EEXIST;
 155           break;
 156
 157         default:
 158           errno = EIO;
 159         }
 160       return -1;
 161     }
 162
 163   return 0;
 164 }
 165
 166 # else /* !Windows */
 167
 168 #  error "This platform lacks a link function, and Gnulib doesn't provide a replacement. This is a bug in Gnulib."
 169
 170 # endif /* !Windows */
 171 #else /* HAVE_LINK */
 172
 173 # undef link
 174
 175 /* Create a hard link from FILE1 to FILE2, working around platform bugs.  */
 176 int
 177 rpl_link (char const *file1, char const *file2)
 178 {
 179   size_t len1;
 180   size_t len2;
 181   struct stat st;
 182
 183   /* Don't allow IRIX to dereference dangling file2 symlink.  */
 184   if (lstat (file2, &st) == 0 || errno == EOVERFLOW)
 185     {
 186       errno = EEXIST;
 187       return -1;
 188     }
 189
 190   /* Reject trailing slashes on non-directories.  */
 191   len1 = strlen (file1);
 192   len2 = strlen (file2);
 193   if ((len1 && file1[len1 - 1] == '/')
 194       || (len2 && file2[len2 - 1] == '/'))
 195     {
 196       /* Let link() decide whether hard-linking directories is legal.
 197          If stat() fails, then link() should fail for the same reason
 198          (although on Solaris 9, link("file/","oops") mistakenly
 199          succeeds); if stat() succeeds, require a directory.  */
 200       if (stat (file1, &st))
 201         return -1;
 202       if (!S_ISDIR (st.st_mode))
 203         {
 204           errno = ENOTDIR;
 205           return -1;
 206         }
 207     }
 208   else
 209     {
 210       /* Fix Cygwin 1.5.x bug where link("a","b/.") creates file "b".  */
 211       char *dir = strdup (file2);
 212       char *p;
 213       if (!dir)
 214         return -1;
 215       /* We already know file2 does not end in slash.  Strip off the
 216          basename, then check that the dirname exists.  */
 217       p = strrchr (dir, '/');
 218       if (p)
 219         {
 220           *p = '\0';
 221           if (stat (dir, &st) != 0 && errno != EOVERFLOW)
 222             {
 223               int saved_errno = errno;
 224               free (dir);
 225               errno = saved_errno;
 226               return -1;
 227             }
 228         }
 229       free (dir);
 230     }
 231   return link (file1, file2);
 232 }
 233 #endif /* HAVE_LINK */