Calculating dependencies... done!
>>> Emerging (1 of 1) net-wireless/madwifi-ng-0.9.2 to /
>>> checking ebuild checksums ;-)
>>> checking auxfile checksums ;-)
>>> checking miscfile checksums ;-)
>>> checking madwifi-0.9.2.tar.bz2 ;-)
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Could not find a usable .config in the kernel source directory.
 * Please ensure that /usr/src/linux points to a configured set of Linux sources.
 * If you are using KBUILD_OUTPUT, please set the environment var so that
 * it points to the necessary object directory so that it might find .config.

!!! ERROR: net-wireless/madwifi-ng-0.9.2 failed.
Call stack:
  ebuild.sh, line 1555:   Called dyn_setup
  ebuild.sh, line 668:   Called pkg_setup
  madwifi-ng-0.9.2.ebuild, line 32:   Called linux-mod_pkg_setup
  linux-mod.eclass, line 432:   Called linux-info_pkg_setup
  linux-info.eclass, line 554:   Called die

!!! Unable to calculate Linux Kernel version