net: add mmsghdr struct check for L2TPV3

The mmsghdr struct is only introduced in Linux 2.6.32; add a
configure check for it and disable L2TPV3 on hosts which are
too old to provide it, rather than simply failing to compile.
Reported-by: Nchenliang <chenliang88@huawei.com>
Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 1404219488-11196-1-git-send-email-arei.gonglei@huawei.com
[PMM: cleaned up commit message and corrected kernel version number]
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

configure

@@ -1711,6 +1711,19 @@ else
     echo big/little test failed
 fi
 
+##########################################
+# L2TPV3 probe
+
+cat > $TMPC <<EOF
+#include <sys/socket.h>
+int main(void) { return sizeof(struct mmsghdr); }
+EOF
+if compile_prog "" "" ; then
+  l2tpv3=yes
+else
+  l2tpv3=no
+fi
+
 ##########################################
 # pkg-config probe
 
@@ -4343,6 +4356,9 @@ fi
 if test "$netmap" = "yes" ; then
   echo "CONFIG_NETMAP=y" >> $config_host_mak
 fi
+if test "$l2tpv3" = "yes" ; then
+  echo "CONFIG_L2TPV3=y" >> $config_host_mak
+fi
 if test "$cap_ng" = "yes" ; then
   echo "CONFIG_LIBCAP=y" >> $config_host_mak
 fi

net/Makefile.objs

@@ -2,7 +2,7 @@ common-obj-y = net.o queue.o checksum.o util.o hub.o
 common-obj-y += socket.o
 common-obj-y += dump.o
 common-obj-y += eth.o
-common-obj-$(CONFIG_LINUX) += l2tpv3.o
+common-obj-$(CONFIG_L2TPV3) += l2tpv3.o
 common-obj-$(CONFIG_POSIX) += tap.o vhost-user.o
 common-obj-$(CONFIG_LINUX) += tap-linux.o
 common-obj-$(CONFIG_WIN32) += tap-win32.o

net/net.c

@@ -806,7 +806,7 @@ static int (* const net_client_init_fun[NET_CLIENT_OPTIONS_KIND_MAX])(
 #ifdef CONFIG_VHOST_NET_USED
         [NET_CLIENT_OPTIONS_KIND_VHOST_USER] = net_init_vhost_user,
 #endif
-#ifdef CONFIG_LINUX
+#ifdef CONFIG_L2TPV3
         [NET_CLIENT_OPTIONS_KIND_L2TPV3]    = net_init_l2tpv3,
 #endif
 };
@@ -845,7 +845,7 @@ static int net_client_init1(const void *object, int is_netdev, Error **errp)
 #ifdef CONFIG_VHOST_NET_USED
         case NET_CLIENT_OPTIONS_KIND_VHOST_USER:
 #endif
-#ifdef CONFIG_LINUX
+#ifdef CONFIG_L2TPV3
         case NET_CLIENT_OPTIONS_KIND_L2TPV3:
 #endif
             break;