Allow zfs_config.h to be included by dependant packages (updated)

We need dependent packages to be able to include zfs_config.h to
build properly.  This was partially solved previously be using
AH_BOTTOM to #undef common #defines (PACKAGE, VERSION, etc) which
autoconf always adds and cannot be easily removed.  This solution
works as long as the zfs_config.h is included before your projects
config.h.  That turns out to be easier said than done.  In particular,
this is a problem when your package includes its config.h using the
-include gcc option which ensures the first thing included is your
config.h.

To handle all cases cleanly I have removed the AH_BOTTOM hack and
replaced it with an AC_CONFIG_HEADERS command.  This command runs
immediately after zfs_config.h is written and with a little awk-foo
it strips the offending #defines from the file.  This eliminates
the problem entirely and makes header safe for inclusion.

Makefile.am

@@ -9,10 +9,11 @@ endif
 SUBDIRS = $(USER_DIR) $(KERNEL_DIR)
 
 AUTOMAKE_OPTIONS = foreign dist-zip
-EXTRA_DIST  = autogen.sh zfs.spec.in zfs-modules.spec.in
+EXTRA_DIST  = autogen.sh config/config.awk
+EXTRA_DIST += zfs.spec.in zfs-modules.spec.in
 EXTRA_DIST += META DISCLAIMER GIT
 EXTRA_DIST += OPENSOLARIS.LICENSE ZFS.RELEASE
-noinst_HEADERS = zfs_config.h zfs_unconfig.h
+noinst_HEADERS = zfs_config.h
 
 distclean-local::
 	-$(RM) -R autom4te*.cache

config/Rules.am

@@ -1,4 +1,4 @@
-DEFAULT_INCLUDES = -I${top_srcdir}
+DEFAULT_INCLUDES = -include ${top_srcdir}/zfs_config.h
 
 # FIXME: Add -Wshadow once everything is working
 AM_CFLAGS  = -Wall -Wstrict-prototypes -fno-strict-aliasing -Werror

config/config.awk

@@ -0,0 +1,15 @@
+# Remove default preprocessor define's from config.h
+#   PACKAGE
+#   PACKAGE_BUGREPORT
+#   PACKAGE_NAME
+#   PACKAGE_STRING
+#   PACKAGE_TARNAME
+#   PACKAGE_VERSION
+#   STDC_HEADERS
+#   VERSION
+
+BEGIN { RS = "" ; FS = "\n" }     \
+	!/.#define PACKAGE./ &&   \
+	!/.#define VERSION./ &&   \
+	!/.#define STDC_HEADERS./ \
+	{ print $0"\n" }

config/kernel.m4

@@ -23,15 +23,13 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_RQ_IS_SYNC
 	ZFS_AC_KERNEL_RQ_FOR_EACH_SEGMENT
 
-	dnl # Kernel build make options
-	dnl # KERNELMAKE_PARAMS="V=1"	# Enable verbose module build
-	KERNELMAKE_PARAMS=
-
 	dnl # -Wall -fno-strict-aliasing -Wstrict-prototypes and other
 	dnl # compiler options are added by the kernel build system.
 	KERNELCPPFLAGS="$KERNELCPPFLAGS -Werror -DHAVE_SPL -D_KERNEL"
 	KERNELCPPFLAGS="$KERNELCPPFLAGS -DTEXT_DOMAIN=\\\"zfs-linux-kernel\\\""
-	KERNELCPPFLAGS="$KERNELCPPFLAGS -I$TOPDIR -I$SPL -I$SPL/include"
+	KERNELCPPFLAGS="$KERNELCPPFLAGS -I$SPL/include"
+	KERNELCPPFLAGS="$KERNELCPPFLAGS -include $SPL/spl_config.h"
+	KERNELCPPFLAGS="$KERNELCPPFLAGS -include $TOPDIR/zfs_config.h"
 
 	if test "$LINUX_OBJ" != "$LINUX"; then
 		KERNELMAKE_PARAMS="$KERNELMAKE_PARAMS O=$LINUX_OBJ"

configure.ac

@@ -35,10 +35,12 @@ AC_LANG(C)
 ZFS_AC_META
 AC_CONFIG_AUX_DIR([config])
 AC_CANONICAL_SYSTEM
-AM_INIT_AUTOMAKE([$ZFS_META_NAME], [$ZFS_META_VERSION])
-AC_CONFIG_HEADERS([zfs_config.h])
-AH_BOTTOM([#include <zfs_unconfig.h>])
 AM_MAINTAINER_MODE
+AM_INIT_AUTOMAKE([$ZFS_META_NAME], [$ZFS_META_VERSION])
+AC_CONFIG_HEADERS([zfs_config.h], [
+	(mv zfs_config.h zfs_config.h.tmp &&
+	awk -f config/config.awk zfs_config.h.tmp >zfs_config.h &&
+	rm zfs_config.h.tmp) || exit 1])
 
 AC_PROG_INSTALL
 AC_PROG_CC

zfs_unconfig.h

@@ -1,12 +0,0 @@
-/*
- * Undefine these symbols to allow other autoheader enabled packages
- * to leverage the ZFS configure checks without a header conflict.
- */
-#undef PACKAGE
-#undef PACKAGE_BUGREPORT
-#undef PACKAGE_NAME
-#undef PACKAGE_STRING
-#undef PACKAGE_TARNAME
-#undef PACKAGE_VERSION
-#undef VERSION
-#undef STDC_HEADERS