m4/fcntl-o.m4

   1 # fcntl-o.m4 serial 7
   2 dnl Copyright (C) 2006, 2009-2021 Free Software Foundation, Inc.
   3 dnl This file is free software; the Free Software Foundation
   4 dnl gives unlimited permission to copy and/or distribute it,
   5 dnl with or without modifications, as long as this notice is preserved.
   6
   7 dnl Written by Paul Eggert.
   8
   9 AC_PREREQ([2.60])
  10
  11 # Test whether the flags O_NOATIME and O_NOFOLLOW actually work.
  12 # Define HAVE_WORKING_O_NOATIME to 1 if O_NOATIME works, or to 0 otherwise.
  13 # Define HAVE_WORKING_O_NOFOLLOW to 1 if O_NOFOLLOW works, or to 0 otherwise.
  14 AC_DEFUN([gl_FCNTL_O_FLAGS],
  15 [
  16   dnl Persuade glibc <fcntl.h> to define O_NOATIME and O_NOFOLLOW.
  17   AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
  18
  19   AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
  20   AC_CHECK_HEADERS_ONCE([unistd.h])
  21   AC_CHECK_FUNCS_ONCE([symlink])
  22   AC_CACHE_CHECK([for working fcntl.h], [gl_cv_header_working_fcntl_h],
  23     [AC_RUN_IFELSE(
  24        [AC_LANG_PROGRAM(
  25           [[#include <sys/types.h>
  26            #include <sys/stat.h>
  27            #if HAVE_UNISTD_H
  28            # include <unistd.h>
  29            #else /* on Windows with MSVC */
  30            # include <io.h>
  31            # include <stdlib.h>
  32            # defined sleep(n) _sleep ((n) * 1000)
  33            #endif
  34            #include <fcntl.h>
  35            ]GL_MDA_DEFINES[
  36            #ifndef O_NOATIME
  37             #define O_NOATIME 0
  38            #endif
  39            #ifndef O_NOFOLLOW
  40             #define O_NOFOLLOW 0
  41            #endif
  42            static int const constants[] =
  43             {
  44               O_CREAT, O_EXCL, O_NOCTTY, O_TRUNC, O_APPEND,
  45               O_NONBLOCK, O_SYNC, O_ACCMODE, O_RDONLY, O_RDWR, O_WRONLY
  46             };
  47           ]],
  48           [[
  49             int result = !constants;
  50             #if HAVE_SYMLINK
  51             {
  52               static char const sym[] = "conftest.sym";
  53               if (symlink ("/dev/null", sym) != 0)
  54                 result |= 2;
  55               else
  56                 {
  57                   int fd = open (sym, O_WRONLY | O_NOFOLLOW | O_CREAT, 0);
  58                   if (fd >= 0)
  59                     {
  60                       close (fd);
  61                       result |= 4;
  62                     }
  63                 }
  64               if (unlink (sym) != 0 || symlink (".", sym) != 0)
  65                 result |= 2;
  66               else
  67                 {
  68                   int fd = open (sym, O_RDONLY | O_NOFOLLOW);
  69                   if (fd >= 0)
  70                     {
  71                       close (fd);
  72                       result |= 4;
  73                     }
  74                 }
  75               unlink (sym);
  76             }
  77             #endif
  78             {
  79               static char const file[] = "confdefs.h";
  80               int fd = open (file, O_RDONLY | O_NOATIME);
  81               if (fd < 0)
  82                 result |= 8;
  83               else
  84                 {
  85                   struct stat st0;
  86                   if (fstat (fd, &st0) != 0)
  87                     result |= 16;
  88                   else
  89                     {
  90                       char c;
  91                       sleep (1);
  92                       if (read (fd, &c, 1) != 1)
  93                         result |= 24;
  94                       else
  95                         {
  96                           if (close (fd) != 0)
  97                             result |= 32;
  98                           else
  99                             {
 100                               struct stat st1;
 101                               if (stat (file, &st1) != 0)
 102                                 result |= 40;
 103                               else
 104                                 if (st0.st_atime != st1.st_atime)
 105                                   result |= 64;
 106                             }
 107                         }
 108                     }
 109                 }
 110             }
 111             return result;]])],
 112        [gl_cv_header_working_fcntl_h=yes],
 113        [case $? in #(
 114         4) gl_cv_header_working_fcntl_h='no (bad O_NOFOLLOW)';; #(
 115         64) gl_cv_header_working_fcntl_h='no (bad O_NOATIME)';; #(
 116         68) gl_cv_header_working_fcntl_h='no (bad O_NOATIME, O_NOFOLLOW)';; #(
 117          *) gl_cv_header_working_fcntl_h='no';;
 118         esac],
 119        [case "$host_os" in
 120                   # Guess 'no' on native Windows.
 121           mingw*) gl_cv_header_working_fcntl_h='no' ;;
 122           *)      gl_cv_header_working_fcntl_h=cross-compiling ;;
 123         esac
 124        ])
 125     ])
 126
 127   case $gl_cv_header_working_fcntl_h in #(
 128   *O_NOATIME* | no | cross-compiling) ac_val=0;; #(
 129   *) ac_val=1;;
 130   esac
 131   AC_DEFINE_UNQUOTED([HAVE_WORKING_O_NOATIME], [$ac_val],
 132     [Define to 1 if O_NOATIME works.])
 133
 134   case $gl_cv_header_working_fcntl_h in #(
 135   *O_NOFOLLOW* | no | cross-compiling) ac_val=0;; #(
 136   *) ac_val=1;;
 137   esac
 138   AC_DEFINE_UNQUOTED([HAVE_WORKING_O_NOFOLLOW], [$ac_val],
 139     [Define to 1 if O_NOFOLLOW works.])
 140 ])