gre: Add kernel GRE support.

This implements the kernel portion of GRE on Linux.  It consists
of a backported module that provides the GRE capabilities of 2.6.32
plus bug fixes to kernels 2.6.18+.

acinclude.m4

@@ -111,6 +111,16 @@ AC_DEFUN([OVS_CHECK_VETH], [
   fi
 ])
 
+AC_DEFUN([OVS_CHECK_GRE], [
+  AC_MSG_CHECKING([whether to build gre module])
+  if test "$sublevel" -ge 18; then
+    AC_MSG_RESULT([yes])
+    AC_SUBST([BUILD_GRE], 1)
+  else
+    AC_MSG_RESULT([no])
+  fi
+])
+
 AC_DEFUN([OVS_CHECK_LOG2_H], [
   AC_MSG_CHECKING([for $KSRC26/include/linux/log2.h])
   if test -e $KSRC26/include/linux/log2.h; then
@@ -153,6 +163,7 @@ AC_DEFUN([OVS_CHECK_LINUX26_COMPAT], [
                   [OVS_DEFINE([HAVE_PROTO_DATA_VALID])])
   OVS_CHECK_LOG2_H
   OVS_CHECK_VETH
+  OVS_CHECK_GRE
   if cmp -s datapath/linux-2.6/kcompat.h.new \
             datapath/linux-2.6/kcompat.h >/dev/null 2>&1; then
     rm datapath/linux-2.6/kcompat.h.new

datapath/linux-2.6/Makefile.main.in

@@ -5,6 +5,7 @@ export top_srcdir = @abs_top_srcdir@
 export KSRC = @KBUILD26@
 export VERSION = @VERSION@
 export BUILD_VETH = @BUILD_VETH@
+export BUILD_GRE = @BUILD_GRE@
 
 include $(srcdir)/../Modules.mk
 include $(srcdir)/Modules.mk

datapath/linux-2.6/Modules.mk

@@ -47,3 +47,26 @@ dist_modules += veth
 build_modules += $(if $(BUILD_VETH),veth)
 veth_sources = linux-2.6/compat-2.6/veth.c
 veth_headers = 
+
+dist_modules += ip_gre
+build_modules += $(if $(BUILD_GRE),ip_gre)
+ip_gre_sources = \
+	linux-2.6/compat-2.6/ip_gre.c \
+	linux-2.6/compat-2.6/net_namespace-ip_gre.c
+ip_gre_headers = \
+	linux-2.6/compat-2.6/compat26.h \
+	linux-2.6/compat-2.6/include/linux/if.h \
+	linux-2.6/compat-2.6/include/linux/in.h \
+	linux-2.6/compat-2.6/include/linux/inetdevice.h \
+	linux-2.6/compat-2.6/include/linux/if_ether.h \
+	linux-2.6/compat-2.6/include/linux/ip.h \
+	linux-2.6/compat-2.6/include/linux/ipv6.h \
+	linux-2.6/compat-2.6/include/linux/netdevice.h \
+	linux-2.6/compat-2.6/include/linux/skbuff.h \
+	linux-2.6/compat-2.6/include/linux/tcp.h \
+	linux-2.6/compat-2.6/include/linux/types.h \
+	linux-2.6/compat-2.6/include/net/dst.h \
+	linux-2.6/compat-2.6/include/net/ipip.h \
+	linux-2.6/compat-2.6/include/net/netns/generic.h \
+	linux-2.6/compat-2.6/include/net/net_namespace.h \
+	linux-2.6/compat-2.6/include/net/route.h