dnl Check to find out whether the running kernel has support for TUN/TAP

AC_DEFUN(tinc_TUNTAP,
[
dnl Check for directory with kernel source... (from ALSA)
AC_CACHE_CHECK([for directory with kernel source], tinc_cv_kerneldir,
[ AC_ARG_WITH(kernel,
    [  --with-kernel=dir       give the directory with kernel sources]
    [                        (default: /usr/src/linux)],
    kerneldir="$withval", kerneldir="/usr/src/linux")
  AC_DEFINE_UNQUOTED(CONFIG_TINC_KERNELDIR, "$kerneldir")
  CONFIG_TINC_KERNELDIR="$kerneldir"
  AC_SUBST(CONFIG_TINC_KERNELDIR)
  AC_MSG_RESULT($kerneldir)
])
AC_CACHE_CHECK([for linux/if_tun.h], tinc_cv_linux_if_tun_h,
[ AC_TRY_COMPILE([linux/if_tun.h],
  [int a = IFF_TAP],
  if_tun_h="linux/if_tun.h",
  [ AC_TRY_COMPILE([$kerneldir/include/linux/if_tun.h],
    [int a = IFF_TAP],
    if_tun_h="$kerneldir/include/linux/if_tun.h",
    if_tun_h="no")
  ])
  if test $if_tun_h = no; then
    AC_MSG_RESULT(none)
  else
    AC_DEFINE(HAVE_TUNTAP)
    AC_DEFINE_UNQUOTED(LINUX_IF_TUN_H, "$if_tun_h")
    AC_SUBST(LINUX_IF_TUN_H)
    AC_MSG_RESULT($if_tun_h)
  fi
  AC_SUBST(HAVE_TUNTAP)
])
])