net: Add interface to bridge when SIOCBRADDIF isn't available

The bridge helper uses the SIOCBRADDIF ioctl to add an inteface to
a bridge.  SIOCBRADDIF is not available on old Linux versions.  This
patch adds support to use the SIOCDEVPRIVATE ioctl with BRCTL_ADD_IF
if SIOCBRADDIF is not available.

Reported-by: Fabien Chouteau <chouteau@adacore.com>
Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

qemu-bridge-helper.c

@@ -35,6 +35,10 @@
 
 #include <linux/sockios.h>
 
+#ifndef SIOCBRADDIF
+#include <linux/if_bridge.h>
+#endif
+
 #include "qemu-queue.h"
 
 #include "net/tap-linux.h"
@@ -221,6 +225,10 @@ static int drop_privileges(void)
 int main(int argc, char **argv)
 {
     struct ifreq ifr;
+#ifndef SIOCBRADDIF
+    unsigned long ifargs[4];
+#endif
+    int ifindex;
     int fd, ctlfd, unixfd = -1;
     int use_vnet = 0;
     int mtu;
@@ -361,9 +369,19 @@ int main(int argc, char **argv)
 
     /* add the interface to the bridge */
     prep_ifreq(&ifr, bridge);
-    ifr.ifr_ifindex = if_nametoindex(iface);
-
-    if (ioctl(ctlfd, SIOCBRADDIF, &ifr) == -1) {
+    ifindex = if_nametoindex(iface);
+#ifndef SIOCBRADDIF
+    ifargs[0] = BRCTL_ADD_IF;
+    ifargs[1] = ifindex;
+    ifargs[2] = 0;
+    ifargs[3] = 0;
+    ifr.ifr_data = (void *)ifargs;
+    ret = ioctl(ctlfd, SIOCDEVPRIVATE, &ifr);
+#else
+    ifr.ifr_ifindex = ifindex;
+    ret = ioctl(ctlfd, SIOCBRADDIF, &ifr);
+#endif
+    if (ret == -1) {
         fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
                 iface, bridge, strerror(errno));
         ret = EXIT_FAILURE;