AC_SEARCH_LIBS([cap_init], [cap], [], [AC_MSG_ERROR([*** POSIX caps library not found])])
AC_CHECK_HEADERS([sys/capability.h], [], [AC_MSG_ERROR([*** POSIX caps headers not found])])
+# This makes sure pkg.m4 is available.
+m4_pattern_forbid([^_?PKG_[A-Z_]+$],[pkg.m4 missing, please install pkg-config])
PKG_CHECK_MODULES(UDEV, [ libudev ])
AC_SUBST(UDEV_CFLAGS)
AC_SUBST(UDEV_LIBS)