m4/linkat.m4

   1 # serial 14
   2 # See if we need to provide linkat replacement.
   3
   4 dnl Copyright (C) 2009-2020 Free Software Foundation, Inc.
   5 dnl This file is free software; the Free Software Foundation
   6 dnl gives unlimited permission to copy and/or distribute it,
   7 dnl with or without modifications, as long as this notice is preserved.
   8
   9 # Written by Eric Blake.
  10
  11 AC_DEFUN([gl_FUNC_LINKAT],
  12 [
  13   AC_REQUIRE([gl_FUNC_OPENAT])
  14   AC_REQUIRE([gl_FUNC_LINK_FOLLOWS_SYMLINK])
  15   AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
  16   AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
  17   AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
  18   AC_CHECK_FUNCS_ONCE([linkat symlink])
  19   if test $ac_cv_func_linkat = no; then
  20     HAVE_LINKAT=0
  21   else
  22     dnl OS X Yosemite has linkat() but it's not sufficient
  23     dnl to our needs since it doesn't support creating
  24     dnl hardlinks to symlinks.  Therefore check for that
  25     dnl capability before considering using the system version.
  26     AC_CACHE_CHECK([whether linkat() can link symlinks],
  27       [gl_cv_func_linkat_nofollow],
  28       [rm -rf conftest.l1 conftest.l2
  29        ln -s target conftest.l1
  30        AC_RUN_IFELSE([AC_LANG_PROGRAM(
  31                         [[#include <fcntl.h>
  32                           #include <unistd.h>
  33                         ]],
  34                         [[return linkat (AT_FDCWD, "conftest.l1", AT_FDCWD,
  35                                          "conftest.l2", 0);
  36                         ]])],
  37          [gl_cv_func_linkat_nofollow=yes],
  38          [gl_cv_func_linkat_nofollow=no],
  39          [case "$host_os" in
  40            darwin*) gl_cv_func_linkat_nofollow="guessing no" ;;
  41            *)       gl_cv_func_linkat_nofollow="guessing yes" ;;
  42           esac])
  43
  44        rm -rf conftest.l1 conftest.l2])
  45
  46     case $gl_cv_func_linkat_nofollow in
  47       *no) LINKAT_SYMLINK_NOTSUP=1 ;;
  48       *yes) LINKAT_SYMLINK_NOTSUP=0 ;;
  49     esac
  50
  51     AC_CACHE_CHECK([whether linkat handles trailing slash correctly],
  52       [gl_cv_func_linkat_slash],
  53       [rm -rf conftest.a conftest.b conftest.c conftest.d conftest.e conftest.s
  54        AC_RUN_IFELSE(
  55          [AC_LANG_PROGRAM(
  56             [[#include <unistd.h>
  57               #include <fcntl.h>
  58               #include <errno.h>
  59               #include <stdio.h>
  60             ]GL_MDA_DEFINES],
  61             [[int result;
  62               int fd;
  63               /* Create a regular file.  */
  64               fd = open ("conftest.a", O_CREAT | O_EXCL | O_WRONLY, 0600);
  65               if (fd < 0)
  66                 return 1;
  67               if (write (fd, "hello", 5) < 5)
  68                 return 2;
  69               if (close (fd) < 0)
  70                 return 3;
  71               /* Test whether hard links are supported on the current
  72                  device.  */
  73               if (linkat (AT_FDCWD, "conftest.a", AT_FDCWD, "conftest.b",
  74                           AT_SYMLINK_FOLLOW) < 0)
  75                 return 0;
  76               result = 0;
  77               /* Test whether a trailing "/" is treated like "/.".  */
  78               if (linkat (AT_FDCWD, "conftest.a/", AT_FDCWD, "conftest.c",
  79                           AT_SYMLINK_FOLLOW) == 0)
  80                 result |= 4;
  81               if (linkat (AT_FDCWD, "conftest.a", AT_FDCWD, "conftest.d/",
  82                           AT_SYMLINK_FOLLOW) == 0)
  83                 result |= 8;
  84
  85               /* On Mac OS X 10.13 a trailing "/" will cause the second path to be
  86                  dereferenced, and thus will succeed on a dangling symlink.  */
  87               if (symlink ("conftest.e", "conftest.s") == 0)
  88                 {
  89                   if (linkat (AT_FDCWD, "conftest.a", AT_FDCWD, "conftest.s/",
  90                       AT_SYMLINK_FOLLOW) == 0)
  91                     result |= 16;
  92                 }
  93
  94               return result;
  95             ]])],
  96          [gl_cv_func_linkat_slash=yes],
  97          [gl_cv_func_linkat_slash=no],
  98          [
  99           case "$host_os" in
 100                              # Guess yes on Linux systems.
 101             linux-* | linux) gl_cv_func_linkat_slash="guessing yes";;
 102                              # Guess yes on glibc systems.
 103             *-gnu* | gnu*)   gl_cv_func_linkat_slash="guessing yes";;
 104                              # If we don't know, obey --enable-cross-guesses.
 105             *)               gl_cv_func_linkat_slash="$gl_cross_guess_normal";;
 106           esac
 107          ])
 108        rm -rf conftest.a conftest.b conftest.c conftest.d conftest.e conftest.s])
 109     case "$gl_cv_func_linkat_slash" in
 110       *yes) gl_linkat_slash_bug=0 ;;
 111       *)    gl_linkat_slash_bug=1 ;;
 112     esac
 113
 114     case "$gl_cv_func_linkat_nofollow" in
 115       *yes) linkat_nofollow=yes ;;
 116       *) linkat_nofollow=no ;;
 117     esac
 118
 119     if test "$linkat_nofollow" != yes \
 120        || test $gl_linkat_slash_bug = 1; then
 121       REPLACE_LINKAT=1
 122       AC_DEFINE_UNQUOTED([LINKAT_TRAILING_SLASH_BUG], [$gl_linkat_slash_bug],
 123         [Define to 1 if linkat fails to recognize a trailing slash.])
 124       AC_DEFINE_UNQUOTED([LINKAT_SYMLINK_NOTSUP], [$LINKAT_SYMLINK_NOTSUP],
 125         [Define to 1 if linkat can create hardlinks to symlinks])
 126     fi
 127   fi
 128 ])