diff --git a/m4/curl-functions.m4 b/m4/curl-functions.m4
index 6cc49f13c..ca19e8981 100644
--- a/m4/curl-functions.m4
+++ b/m4/curl-functions.m4
@@ -21,7 +21,7 @@
 #***************************************************************************
 
 # File version for 'aclocal' use. Keep it a single number.
-# serial 66
+# serial 67
 
 
 dnl CURL_INCLUDES_ARPA_INET
@@ -1094,6 +1094,7 @@ AC_DEFUN([CURL_CHECK_FUNC_FCNTL], [
     AC_DEFINE_UNQUOTED(HAVE_FCNTL, 1,
       [Define to 1 if you have the fcntl function.])
     ac_cv_func_fcntl="yes"
+    CURL_CHECK_FUNC_FCNTL_FD_CLOEXEC
     CURL_CHECK_FUNC_FCNTL_O_NONBLOCK
   else
     AC_MSG_RESULT([no])
@@ -1102,6 +1103,69 @@ AC_DEFUN([CURL_CHECK_FUNC_FCNTL], [
 ])
 
 
+dnl CURL_CHECK_FUNC_FCNTL_FD_CLOEXEC
+dnl -------------------------------------------------
+dnl Verify if fcntl with status flag FD_CLOEXEC is
+dnl available, can be compiled, and seems to work. If
+dnl all of these are true, then HAVE_FCNTL_FD_CLOEXEC
+dnl will be defined.
+
+AC_DEFUN([CURL_CHECK_FUNC_FCNTL_FD_CLOEXEC], [
+  #
+  tst_compi_fcntl_fd_cloexec="unknown"
+  tst_allow_fcntl_fd_cloexec="unknown"
+  #
+  case $host_os in
+    some_systems)
+      dnl FD_CLOEXEC does not work on these platforms
+      curl_disallow_fcntl_fd_cloexec="yes"
+      ;;
+  esac
+  #
+  if test "$ac_cv_func_fcntl" = "yes"; then
+    AC_MSG_CHECKING([if fcntl FD_CLOEXEC is compilable])
+    AC_COMPILE_IFELSE([
+      AC_LANG_PROGRAM([[
+        $curl_includes_fcntl
+      ]],[[
+        int flags = 0;
+        if(0 != fcntl(0, F_SETFD, flags | FD_CLOEXEC))
+          return 1;
+      ]])
+    ],[
+      AC_MSG_RESULT([yes])
+      tst_compi_fcntl_fd_cloexec="yes"
+    ],[
+      AC_MSG_RESULT([no])
+      tst_compi_fcntl_fd_cloexec="no"
+    ])
+  fi
+  #
+  if test "$tst_compi_fcntl_fd_cloexec" = "yes"; then
+    AC_MSG_CHECKING([if fcntl FD_CLOEXEC usage allowed])
+    if test "x$curl_disallow_fcntl_fd_cloexec" != "xyes"; then
+      AC_MSG_RESULT([yes])
+      tst_allow_fcntl_fd_cloexec="yes"
+    else
+      AC_MSG_RESULT([no])
+      tst_allow_fcntl_fd_cloexec="no"
+    fi
+  fi
+  #
+  AC_MSG_CHECKING([if fcntl FD_CLOEXEC might be used])
+  if test "$tst_compi_fcntl_fd_cloexec" = "yes" &&
+     test "$tst_allow_fcntl_fd_cloexec" = "yes"; then
+    AC_MSG_RESULT([yes])
+    AC_DEFINE_UNQUOTED(HAVE_FCNTL_FD_CLOEXEC, 1,
+      [Define to 1 if you have a working fcntl FD_CLOEXEC function.])
+    ac_cv_func_fcntl_fd_cloexec="yes"
+  else
+    AC_MSG_RESULT([no])
+    ac_cv_func_fcntl_fd_cloexec="no"
+  fi
+])
+
+
 dnl CURL_CHECK_FUNC_FCNTL_O_NONBLOCK
 dnl -------------------------------------------------
 dnl Verify if fcntl with status flag O_NONBLOCK is
@@ -5617,6 +5681,8 @@ AC_DEFUN([CURL_CHECK_FUNC_SOCKET], [
     AC_DEFINE_UNQUOTED(HAVE_SOCKET, 1,
       [Define to 1 if you have the socket function.])
     ac_cv_func_socket="yes"
+    CURL_CHECK_FUNC_SOCKET_SOCK_CLOEXEC
+    CURL_CHECK_FUNC_SOCKET_SOCK_NONBLOCK
   else
     AC_MSG_RESULT([no])
     ac_cv_func_socket="no"
@@ -5624,6 +5690,140 @@ AC_DEFUN([CURL_CHECK_FUNC_SOCKET], [
 ])
 
 
+dnl CURL_CHECK_FUNC_SOCKET_SOCK_CLOEXEC
+dnl -------------------------------------------------
+dnl Verify if socket with type flag SOCK_CLOEXEC is
+dnl available, can be compiled, and seems to work. If
+dnl all of these are true, then HAVE_SOCKET_SOCK_CLOEXEC
+dnl will be defined.
+
+AC_DEFUN([CURL_CHECK_FUNC_SOCKET_SOCK_CLOEXEC], [
+  AC_REQUIRE([CURL_INCLUDES_WINSOCK2])dnl
+  AC_REQUIRE([CURL_INCLUDES_SYS_SOCKET])dnl
+  AC_REQUIRE([CURL_INCLUDES_SOCKET])dnl
+  #
+  tst_compi_socket_sock_cloexec="unknown"
+  tst_allow_socket_sock_cloexec="unknown"
+  #
+  case $host_os in
+    some_systems)
+      dnl socket SOCK_CLOEXEC does not work
+      curl_disallow_socket_sock_cloexec="yes"
+      ;;
+  esac
+  #
+  if test "$ac_cv_func_socket" = "yes"; then
+    AC_MSG_CHECKING([if socket SOCK_CLOEXEC is compilable])
+    AC_COMPILE_IFELSE([
+        $curl_includes_winsock2
+        $curl_includes_sys_socket
+        $curl_includes_socket
+      ]],[[
+        int flags = 0;
+        if(0 != socket(0, flags | SOCK_CLOEXEC, 0))
+          return 1;
+      ]])
+    ],[
+      AC_MSG_RESULT([yes])
+      tst_compi_socket_sock_cloexec="yes"
+    ],[
+      AC_MSG_RESULT([no])
+      tst_compi_socket_sock_cloexec="no"
+    ])
+  fi
+  #
+  if test "$tst_compi_socket_sock_cloexec" = "yes"; then
+    AC_MSG_CHECKING([if socket SOCK_CLOEXEC usage allowed])
+    if test "x$curl_disallow_socket_sock_cloexec" != "xyes"; then
+      AC_MSG_RESULT([yes])
+      tst_allow_socket_sock_cloexec="yes"
+    else
+      AC_MSG_RESULT([no])
+      tst_allow_socket_sock_cloexec="no"
+    fi
+  fi
+  #
+  AC_MSG_CHECKING([if socket SOCK_CLOEXEC might be used])
+  if test "$tst_compi_socket_sock_cloexec" = "yes" &&
+     test "$tst_allow_socket_sock_cloexec" = "yes"; then
+    AC_MSG_RESULT([yes])
+    AC_DEFINE_UNQUOTED(HAVE_SOCKET_SOCK_CLOEXEC, 1,
+      [Define to 1 if you have a working socket SOCK_CLOEXEC function.])
+    ac_cv_func_socket_sock_cloexec="yes"
+  else
+    AC_MSG_RESULT([no])
+    ac_cv_func_socket_sock_cloexec="no"
+  fi
+])
+
+
+dnl CURL_CHECK_FUNC_SOCKET_SOCK_NONBLOCK
+dnl -------------------------------------------------
+dnl Verify if socket with type flag SOCK_NONBLOCK is
+dnl available, can be compiled, and seems to work. If
+dnl all of these are true, then HAVE_SOCKET_SOCK_NONBLOCK
+dnl will be defined.
+
+AC_DEFUN([CURL_CHECK_FUNC_SOCKET_SOCK_NONBLOCK], [
+  AC_REQUIRE([CURL_INCLUDES_WINSOCK2])dnl
+  AC_REQUIRE([CURL_INCLUDES_SYS_SOCKET])dnl
+  AC_REQUIRE([CURL_INCLUDES_SOCKET])dnl
+  #
+  tst_compi_socket_sock_nonblock="unknown"
+  tst_allow_socket_sock_nonblock="unknown"
+  #
+  case $host_os in
+    some_systems)
+      dnl socket SOCK_NONBLOCK does not work
+      curl_disallow_socket_sock_nonblock="yes"
+      ;;
+  esac
+  #
+  if test "$ac_cv_func_socket" = "yes"; then
+    AC_MSG_CHECKING([if socket SOCK_NONBLOCK is compilable])
+    AC_COMPILE_IFELSE([
+        $curl_includes_winsock2
+        $curl_includes_sys_socket
+        $curl_includes_socket
+      ]],[[
+        int flags = 0;
+        if(0 != socket(0, flags | SOCK_NONBLOCK, 0))
+          return 1;
+      ]])
+    ],[
+      AC_MSG_RESULT([yes])
+      tst_compi_socket_sock_nonblock="yes"
+    ],[
+      AC_MSG_RESULT([no])
+      tst_compi_socket_sock_nonblock="no"
+    ])
+  fi
+  #
+  if test "$tst_compi_socket_sock_nonblock" = "yes"; then
+    AC_MSG_CHECKING([if socket SOCK_NONBLOCK usage allowed])
+    if test "x$curl_disallow_socket_sock_nonblock" != "xyes"; then
+      AC_MSG_RESULT([yes])
+      tst_allow_socket_sock_nonblock="yes"
+    else
+      AC_MSG_RESULT([no])
+      tst_allow_socket_sock_nonblock="no"
+    fi
+  fi
+  #
+  AC_MSG_CHECKING([if socket SOCK_NONBLOCK might be used])
+  if test "$tst_compi_socket_sock_nonblock" = "yes" &&
+     test "$tst_allow_socket_sock_nonblock" = "yes"; then
+    AC_MSG_RESULT([yes])
+    AC_DEFINE_UNQUOTED(HAVE_SOCKET_SOCK_NONBLOCK, 1,
+      [Define to 1 if you have a working socket SOCK_NONBLOCK function.])
+    ac_cv_func_socket_sock_nonblock="yes"
+  else
+    AC_MSG_RESULT([no])
+    ac_cv_func_socket_sock_nonblock="no"
+  fi
+])
+
+
 dnl CURL_CHECK_FUNC_SOCKETPAIR
 dnl -------------------------------------------------
 dnl Verify if socketpair is available, prototyped, and
@@ -5706,6 +5906,8 @@ AC_DEFUN([CURL_CHECK_FUNC_SOCKETPAIR], [
     AC_DEFINE_UNQUOTED(HAVE_SOCKETPAIR, 1,
       [Define to 1 if you have the socketpair function.])
     ac_cv_func_socketpair="yes"
+    CURL_CHECK_FUNC_SOCKETPAIR_SOCK_CLOEXEC
+    CURL_CHECK_FUNC_SOCKETPAIR_SOCK_NONBLOCK
   else
     AC_MSG_RESULT([no])
     ac_cv_func_socketpair="no"
@@ -5713,6 +5915,138 @@ AC_DEFUN([CURL_CHECK_FUNC_SOCKETPAIR], [
 ])
 
 
+dnl CURL_CHECK_FUNC_SOCKETPAIR_SOCK_CLOEXEC
+dnl -------------------------------------------------
+dnl Verify if socketpair with type flag SOCK_CLOEXEC is
+dnl available, can be compiled, and seems to work. If
+dnl all of these are true, then HAVE_SOCKETPAIR_SOCK_CLOEXEC
+dnl will be defined.
+
+AC_DEFUN([CURL_CHECK_FUNC_SOCKETPAIR_SOCK_CLOEXEC], [
+  AC_REQUIRE([CURL_INCLUDES_SYS_SOCKET])dnl
+  AC_REQUIRE([CURL_INCLUDES_SOCKET])dnl
+  #
+  tst_compi_socketpair_sock_cloexec="unknown"
+  tst_allow_socketpair_sock_cloexec="unknown"
+  #
+  case $host_os in
+    some_systems)
+      dnl socketpair SOCK_CLOEXEC does not work
+      curl_disallow_socketpair_sock_cloexec="yes"
+      ;;
+  esac
+  #
+  if test "$ac_cv_func_socketpair" = "yes"; then
+    AC_MSG_CHECKING([if socketpair SOCK_CLOEXEC is compilable])
+    AC_COMPILE_IFELSE([
+        $curl_includes_sys_socket
+        $curl_includes_socket
+      ]],[[
+        int sv[2];
+        int flags = 0;
+        if(0 != socketpair(0, flags | SOCK_CLOEXEC, 0, sv))
+          return 1;
+      ]])
+    ],[
+      AC_MSG_RESULT([yes])
+      tst_compi_socketpair_sock_cloexec="yes"
+    ],[
+      AC_MSG_RESULT([no])
+      tst_compi_socketpair_sock_cloexec="no"
+    ])
+  fi
+  #
+  if test "$tst_compi_socketpair_sock_cloexec" = "yes"; then
+    AC_MSG_CHECKING([if socketpair SOCK_CLOEXEC usage allowed])
+    if test "x$curl_disallow_socketpair_sock_cloexec" != "xyes"; then
+      AC_MSG_RESULT([yes])
+      tst_allow_socketpair_sock_cloexec="yes"
+    else
+      AC_MSG_RESULT([no])
+      tst_allow_socketpair_sock_cloexec="no"
+    fi
+  fi
+  #
+  AC_MSG_CHECKING([if socketpair SOCK_CLOEXEC might be used])
+  if test "$tst_compi_socketpair_sock_cloexec" = "yes" &&
+     test "$tst_allow_socketpair_sock_cloexec" = "yes"; then
+    AC_MSG_RESULT([yes])
+    AC_DEFINE_UNQUOTED(HAVE_SOCKETPAIR_SOCK_CLOEXEC, 1,
+      [Define to 1 if you have a working socketpair SOCK_CLOEXEC function.])
+    ac_cv_func_socketpair_sock_cloexec="yes"
+  else
+    AC_MSG_RESULT([no])
+    ac_cv_func_socketpair_sock_cloexec="no"
+  fi
+])
+
+
+dnl CURL_CHECK_FUNC_SOCKETPAIR_SOCK_NONBLOCK
+dnl -------------------------------------------------
+dnl Verify if socketpair with type flag SOCK_NONBLOCK is
+dnl available, can be compiled, and seems to work. If
+dnl all of these are true, then HAVE_SOCKETPAIR_SOCK_NONBLOCK
+dnl will be defined.
+
+AC_DEFUN([CURL_CHECK_FUNC_SOCKETPAIR_SOCK_NONBLOCK], [
+  AC_REQUIRE([CURL_INCLUDES_SYS_SOCKET])dnl
+  AC_REQUIRE([CURL_INCLUDES_SOCKET])dnl
+  #
+  tst_compi_socketpair_sock_nonblock="unknown"
+  tst_allow_socketpair_sock_nonblock="unknown"
+  #
+  case $host_os in
+    some_systems)
+      dnl socketpair SOCK_NONBLOCK does not work
+      curl_disallow_socketpair_sock_nonblock="yes"
+      ;;
+  esac
+  #
+  if test "$ac_cv_func_socketpair" = "yes"; then
+    AC_MSG_CHECKING([if socketpair SOCK_NONBLOCK is compilable])
+    AC_COMPILE_IFELSE([
+        $curl_includes_sys_socket
+        $curl_includes_socket
+      ]],[[
+        int sv[2];
+        int flags = 0;
+        if(0 != socketpair(0, flags | SOCK_NONBLOCK, 0, sv))
+          return 1;
+      ]])
+    ],[
+      AC_MSG_RESULT([yes])
+      tst_compi_socketpair_sock_nonblock="yes"
+    ],[
+      AC_MSG_RESULT([no])
+      tst_compi_socketpair_sock_nonblock="no"
+    ])
+  fi
+  #
+  if test "$tst_compi_socketpair_sock_nonblock" = "yes"; then
+    AC_MSG_CHECKING([if socketpair SOCK_NONBLOCK usage allowed])
+    if test "x$curl_disallow_socketpair_sock_nonblock" != "xyes"; then
+      AC_MSG_RESULT([yes])
+      tst_allow_socketpair_sock_nonblock="yes"
+    else
+      AC_MSG_RESULT([no])
+      tst_allow_socketpair_sock_nonblock="no"
+    fi
+  fi
+  #
+  AC_MSG_CHECKING([if socketpair SOCK_NONBLOCK might be used])
+  if test "$tst_compi_socketpair_sock_nonblock" = "yes" &&
+     test "$tst_allow_socketpair_sock_nonblock" = "yes"; then
+    AC_MSG_RESULT([yes])
+    AC_DEFINE_UNQUOTED(HAVE_SOCKETPAIR_SOCK_NONBLOCK, 1,
+      [Define to 1 if you have a working socketpair SOCK_NONBLOCK function.])
+    ac_cv_func_socketpair_sock_nonblock="yes"
+  else
+    AC_MSG_RESULT([no])
+    ac_cv_func_socketpair_sock_nonblock="no"
+  fi
+])
+
+
 dnl CURL_CHECK_FUNC_STRCASECMP
 dnl -------------------------------------------------
 dnl Verify if strcasecmp is available, prototyped, and