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