Determine if a kernel is built with a specific option?

[Andrew Thompson]

On Mon, Jan 12, 2009 at 11:55:11AM +0000, Andrew Brampton wrote:
> 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.

I believe the correct way is to read kern.features from sysctl and the
appropriate code marks it with FEATURE(name, "description");

Having said that the polling code does not set this so would need to be
added.


Andrew