add vif using local interface index instead of IP

When routing daemon wants to enable forwarding of multicast traffic it
performs something like:

       struct vifctl vc = {
               .vifc_vifi  = 1,
               .vifc_flags = 0,
               .vifc_threshold = 1,
               .vifc_rate_limit = 0,
               .vifc_lcl_addr = ip, /* <--- ip address of physical
interface, e.g. eth0 */
               .vifc_rmt_addr.s_addr = htonl(INADDR_ANY),
         };
       setsockopt(fd, IPPROTO_IP, MRT_ADD_VIF, &vc, sizeof(vc));

This leads (in the kernel) to calling  vif_add() function call which
search the (physical) device using assigned IP address:
       dev = ip_dev_find(net, vifc->vifc_lcl_addr.s_addr);

The current API (struct vifctl) does not allow to specify an
interface other way than using it's IP, and if there are more than a
single interface with specified IP only the first one will be found.

The attached patch (against 2.6.30.4) allows to specify an interface
by its index, instead of IP address:

       struct vifctl vc = {
               .vifc_vifi  = 1,
               .vifc_flags = VIFF_USE_IFINDEX,   /* NEW */
               .vifc_threshold = 1,
               .vifc_rate_limit = 0,
               .vifc_lcl_ifindex = if_nametoindex("eth0"),   /* NEW */
               .vifc_rmt_addr.s_addr = htonl(INADDR_ANY),
         };
       setsockopt(fd, IPPROTO_IP, MRT_ADD_VIF, &vc, sizeof(vc));

Signed-off-by: Ilia K. <mail4ilia@gmail.com>

=== modified file 'include/linux/mroute.h'
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 1 deletions

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 630a56df7b47..c757f0b4b74c 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -469,8 +469,18 @@ static int vif_add(struct net *net, struct vifctl *vifc, int mrtsock)
                         return err;
                 }
                 break;
+
+        case VIFF_USE_IFINDEX:
         case 0:
-                dev = ip_dev_find(net, vifc->vifc_lcl_addr.s_addr);
+                if (vifc->vifc_flags == VIFF_USE_IFINDEX) {
+                        dev = dev_get_by_index(net, vifc->vifc_lcl_ifindex);
+                        if (dev && dev->ip_ptr == NULL) {
+                                dev_put(dev);
+                                return -EADDRNOTAVAIL;
+                        }
+                } else
+                        dev = ip_dev_find(net, vifc->vifc_lcl_addr.s_addr);
+
                 if (!dev)
                         return -EADDRNOTAVAIL;
                 err = dev_set_allmulti(dev, 1);