emacs/m4/dup2.m4

#serial 25
dnl Copyright (C) 2002, 2005, 2007, 2009-2020 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

AC_DEFUN([gl_FUNC_DUP2],
[
  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
  AC_REQUIRE([AC_CANONICAL_HOST])
  m4_ifdef([gl_FUNC_DUP2_OBSOLETE], [
    AC_CHECK_FUNCS_ONCE([dup2])
    if test $ac_cv_func_dup2 = no; then
      HAVE_DUP2=0
    fi
  ], [
    AC_DEFINE([HAVE_DUP2], [1], [Define to 1 if you have the 'dup2' function.])
  ])
  if test $HAVE_DUP2 = 1; then
    AC_CACHE_CHECK([whether dup2 works], [gl_cv_func_dup2_works],
      [AC_RUN_IFELSE([
         AC_LANG_PROGRAM(
           [[#include <errno.h>
             #include <fcntl.h>
             #include <limits.h>
             #include <sys/resource.h>
             #include <unistd.h>
             #ifndef RLIM_SAVED_CUR
             # define RLIM_SAVED_CUR RLIM_INFINITY
             #endif
             #ifndef RLIM_SAVED_MAX
             # define RLIM_SAVED_MAX RLIM_INFINITY
             #endif
           ]],
           [[int result = 0;
             int bad_fd = INT_MAX;
             struct rlimit rlim;
             if (getrlimit (RLIMIT_NOFILE, &rlim) == 0
                 && 0 <= rlim.rlim_cur && rlim.rlim_cur <= INT_MAX
                 && rlim.rlim_cur != RLIM_INFINITY
                 && rlim.rlim_cur != RLIM_SAVED_MAX
                 && rlim.rlim_cur != RLIM_SAVED_CUR)
               bad_fd = rlim.rlim_cur;
             #ifdef FD_CLOEXEC
               if (fcntl (1, F_SETFD, FD_CLOEXEC) == -1)
                 result |= 1;
             #endif
             if (dup2 (1, 1) != 1)
               result |= 2;
             #ifdef FD_CLOEXEC
               if (fcntl (1, F_GETFD) != FD_CLOEXEC)
                 result |= 4;
             #endif
             close (0);
             if (dup2 (0, 0) != -1)
               result |= 8;
             /* Many gnulib modules require POSIX conformance of EBADF.  */
             if (dup2 (2, bad_fd) == -1 && errno != EBADF)
               result |= 16;
             /* Flush out some cygwin core dumps.  */
             if (dup2 (2, -1) != -1 || errno != EBADF)
               result |= 32;
             dup2 (2, 255);
             dup2 (2, 256);
             /* On OS/2 kLIBC, dup2() does not work on a directory fd.  */
             {
               int fd = open (".", O_RDONLY);
               if (fd == -1)
                 result |= 64;
               else if (dup2 (fd, fd + 1) == -1)
                 result |= 128;

               close (fd);
             }
             return result;]])
        ],
        [gl_cv_func_dup2_works=yes], [gl_cv_func_dup2_works=no],
        [case "$host_os" in
           mingw*) # on this platform, dup2 always returns 0 for success
             gl_cv_func_dup2_works="guessing no" ;;
           cygwin*) # on cygwin 1.5.x, dup2(1,1) returns 0
             gl_cv_func_dup2_works="guessing no" ;;
           aix* | freebsd*)
                   # on AIX 7.1 and FreeBSD 6.1, dup2 (1,toobig) gives EMFILE,
                   # not EBADF.
             gl_cv_func_dup2_works="guessing no" ;;
           haiku*) # on Haiku alpha 2, dup2(1, 1) resets FD_CLOEXEC.
             gl_cv_func_dup2_works="guessing no" ;;
           *-android*) # implemented using dup3(), which fails if oldfd == newfd
             gl_cv_func_dup2_works="guessing no" ;;
           os2*) # on OS/2 kLIBC, dup2() does not work on a directory fd.
             gl_cv_func_dup2_works="guessing no" ;;
           *) gl_cv_func_dup2_works="guessing yes" ;;
         esac])
      ])
    case "$gl_cv_func_dup2_works" in
      *yes) ;;
      *)
        REPLACE_DUP2=1
        AC_CHECK_FUNCS([setdtablesize])
        ;;
    esac
  fi
  dnl Replace dup2() for supporting the gnulib-defined fchdir() function,
  dnl to keep fchdir's bookkeeping up-to-date.
  m4_ifdef([gl_FUNC_FCHDIR], [
    gl_TEST_FCHDIR
    if test $HAVE_FCHDIR = 0; then
      if test $HAVE_DUP2 = 1; then
        REPLACE_DUP2=1
      fi
    fi
  ])
])

# Prerequisites of lib/dup2.c.
AC_DEFUN([gl_PREREQ_DUP2], [])