net/sock: option to specify local address

Add an option to specify the host IP to send multicast packets from,
when using a multicast socket for networking. The option takes an IP
address and sets the IP_MULTICAST_IF socket option, which causes the
packets to use that IP's interface as an egress.

This is useful if the host machine has several interfaces with several
virtual networks across disparate interfaces.

Signed-off-by: Mike Ryan <mikeryan@ISI.EDU>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 39 insertions, 13 deletions

diff --git a/net/socket.c b/net/socket.c
index 1c4e153e3..916c2a8e1 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -149,7 +149,7 @@ static void net_socket_send_dgram(void *opaque)
     qemu_send_packet(&s->nc, s->buf, size);
 }
 
-static int net_socket_mcast_create(struct sockaddr_in *mcastaddr)
+static int net_socket_mcast_create(struct sockaddr_in *mcastaddr, struct in_addr *localaddr)
 {
     struct ip_mreq imr;
     int fd;
@@ -183,7 +183,11 @@ static int net_socket_mcast_create(struct sockaddr_in *mcastaddr)
 
     /* Add host to multicast group */
     imr.imr_multiaddr = mcastaddr->sin_addr;
-    imr.imr_interface.s_addr = htonl(INADDR_ANY);
+    if (localaddr) {
+        imr.imr_interface = *localaddr;
+    } else {
+        imr.imr_interface.s_addr = htonl(INADDR_ANY);
+    }
 
     ret = setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP,
                      (const char *)&imr, sizeof(struct ip_mreq));
@@ -201,6 +205,15 @@ static int net_socket_mcast_create(struct sockaddr_in *mcastaddr)
 	goto fail;
     }
 
+    /* If a bind address is given, only send packets from that address */
+    if (localaddr != NULL) {
+        ret = setsockopt(fd, IPPROTO_IP, IP_MULTICAST_IF, localaddr, sizeof(*localaddr));
+        if (ret < 0) {
+            perror("setsockopt(IP_MULTICAST_IF)");
+            goto fail;
+        }
+    }
+
     socket_set_nonblock(fd);
     return fd;
 fail:
@@ -248,7 +261,7 @@ static NetSocketState *net_socket_fd_init_dgram(VLANState *vlan,
 		return NULL;
 	    }
 	    /* clone dgram socket */
-	    newfd = net_socket_mcast_create(&saddr);
+	    newfd = net_socket_mcast_create(&saddr, NULL);
 	    if (newfd < 0) {
 		/* error already reported by net_socket_mcast_create() */
 		close(fd);
@@ -468,17 +481,26 @@ static int net_socket_connect_init(VLANState *vlan,
 static int net_socket_mcast_init(VLANState *vlan,
                                  const char *model,
                                  const char *name,
-                                 const char *host_str)
+                                 const char *host_str,
+                                 const char *localaddr_str)
 {
     NetSocketState *s;
     int fd;
     struct sockaddr_in saddr;
+    struct in_addr localaddr, *param_localaddr;
 
     if (parse_host_port(&saddr, host_str) < 0)
         return -1;
 
+    if (localaddr_str != NULL) {
+        if (inet_aton(localaddr_str, &localaddr) == 0)
+            return -1;
+        param_localaddr = &localaddr;
+    } else {
+        param_localaddr = NULL;
+    }
 
-    fd = net_socket_mcast_create(&saddr);
+    fd = net_socket_mcast_create(&saddr, param_localaddr);
     if (fd < 0)
 	return -1;
 
@@ -505,8 +527,9 @@ int net_init_socket(QemuOpts *opts,
 
         if (qemu_opt_get(opts, "listen") ||
             qemu_opt_get(opts, "connect") ||
-            qemu_opt_get(opts, "mcast")) {
-            error_report("listen=, connect= and mcast= is invalid with fd=");
+            qemu_opt_get(opts, "mcast") ||
+            qemu_opt_get(opts, "localaddr")) {
+            error_report("listen=, connect=, mcast= and localaddr= is invalid with fd=\n");
             return -1;
         }
 
@@ -524,8 +547,9 @@ int net_init_socket(QemuOpts *opts,
 
         if (qemu_opt_get(opts, "fd") ||
             qemu_opt_get(opts, "connect") ||
-            qemu_opt_get(opts, "mcast")) {
-            error_report("fd=, connect= and mcast= is invalid with listen=");
+            qemu_opt_get(opts, "mcast") ||
+            qemu_opt_get(opts, "localaddr")) {
+            error_report("fd=, connect=, mcast= and localaddr= is invalid with listen=\n");
             return -1;
         }
 
@@ -539,8 +563,9 @@ int net_init_socket(QemuOpts *opts,
 
         if (qemu_opt_get(opts, "fd") ||
             qemu_opt_get(opts, "listen") ||
-            qemu_opt_get(opts, "mcast")) {
-            error_report("fd=, listen= and mcast= is invalid with connect=");
+            qemu_opt_get(opts, "mcast") ||
+            qemu_opt_get(opts, "localaddr")) {
+            error_report("fd=, listen=, mcast= and localaddr= is invalid with connect=\n");
             return -1;
         }
 
@@ -550,7 +575,7 @@ int net_init_socket(QemuOpts *opts,
             return -1;
         }
     } else if (qemu_opt_get(opts, "mcast")) {
-        const char *mcast;
+        const char *mcast, *localaddr;
 
         if (qemu_opt_get(opts, "fd") ||
             qemu_opt_get(opts, "connect") ||
@@ -560,8 +585,9 @@ int net_init_socket(QemuOpts *opts,
         }
 
         mcast = qemu_opt_get(opts, "mcast");
+        localaddr = qemu_opt_get(opts, "localaddr");
 
-        if (net_socket_mcast_init(vlan, "socket", name, mcast) == -1) {
+        if (net_socket_mcast_init(vlan, "socket", name, mcast, localaddr) == -1) {
             return -1;
         }
     } else {