Determine if a kernel is built with a specific option?

[Andrew Brampton]

Hi,
I was wondering how a autoconf configure script can determine if the
kernel is built with a particular option. In this case the code I have
can make use of the FreeBSD polling driver, which by default isn't
built into a kernel. So I want my configure script to determine if the
kernel supports it, if so sets a #define, otherwise doesn't.

In the past I have basically hacked my way though these configure
scripts by looking at other examples. One such example I found was for
Linux, which does something like this:

AC_CACHE_CHECK(for device polling kernel extension, ac_cv_linux_poll_extension,
[if grep polling `find_linuxpath include/linux/netdevice.h` >/dev/null
2>&1; then
  ac_cv_linux_poll_extension=yes
else ac_cv_linux_poll_extension=no; fi])
if test $ac_cv_linux_poll_extension = yes; then
    AC_DEFINE(HAVE_LINUX_POLLING)
fi

So I simply want to figure out an equalavant check I can do on FreeBSD.

thanks
Andrew