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[Qemu-devel] [PATCH] add a command line option to specify the IP address


From: Mike Ryan
Subject: [Qemu-devel] [PATCH] add a command line option to specify the IP address to send multicast packets from
Date: Wed, 17 Nov 2010 17:16:26 -0800
User-agent: Mutt/1.5.20 (2009-06-14)

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.
---
 net.c           |    4 ++++
 net/socket.c    |   46 ++++++++++++++++++++++++++++++++++------------
 qemu-options.hx |   11 +++++++++--
 3 files changed, 47 insertions(+), 14 deletions(-)

diff --git a/net.c b/net.c
index c5e6063..9ba5be2 100644
--- a/net.c
+++ b/net.c
@@ -1050,6 +1050,10 @@ static const struct {
                 .name = "mcast",
                 .type = QEMU_OPT_STRING,
                 .help = "UDP multicast address and port number",
+            }, {
+                .name = "localaddr",
+                .type = QEMU_OPT_STRING,
+                .help = "source address for multicast packets",
             },
             { /* end of list */ }
         },
diff --git a/net/socket.c b/net/socket.c
index 1c4e153..d443f4c 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;
@@ -201,6 +201,15 @@ 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 +257,7 @@ 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 +477,26 @@ 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 +523,9 @@ 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 +543,9 @@ 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 +559,9 @@ 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 +571,7 @@ 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 +581,9 @@ 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 {
diff --git a/qemu-options.hx b/qemu-options.hx
index 4d99a58..accd16a 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1061,8 +1061,9 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
 #endif
     "-net 
socket[,vlan=n][,name=str][,fd=h][,listen=[host]:port][,connect=host:port]\n"
     "                connect the vlan 'n' to another VLAN using a socket 
connection\n"
-    "-net socket[,vlan=n][,name=str][,fd=h][,mcast=maddr:port]\n"
+    "-net 
socket[,vlan=n][,name=str][,fd=h][,mcast=maddr:port[,localaddr=addr]]\n"
     "                connect the vlan 'n' to multicast maddr and port\n"
+    "                use 'localaddr=addr' to specify the host address to send 
packets from\n"
 #ifdef CONFIG_VDE
     "-net 
vde[,vlan=n][,name=str][,sock=socketpath][,port=n][,group=groupname][,mode=octalmode]\n"
     "                connect the vlan 'n' to port 'n' of a vde switch 
running\n"
@@ -1256,7 +1257,7 @@ qemu linux.img -net nic,macaddr=52:54:00:12:34:57 \
                -net socket,connect=127.0.0.1:1234
 @end example
 
address@hidden -net socket[,address@hidden,address@hidden,address@hidden 
[,address@hidden:@var{port}]
address@hidden -net 
socket[,address@hidden,address@hidden,address@hidden,address@hidden:@var{port}[,address@hidden
 
 Create a VLAN @var{n} shared with another QEMU virtual
 machines using a UDP multicast socket, effectively making a bus for
@@ -1296,6 +1297,12 @@ qemu linux.img -net nic,macaddr=52:54:00:12:34:56 \
 /path/to/linux ubd0=/path/to/root_fs eth0=mcast
 @end example
 
+Example (send packets from host's 1.2.3.4):
address@hidden
+qemu linux.img -net nic,macaddr=52:54:00:12:34:56 \
+               -net socket,mcast=239.192.168.1:1102,localaddr=1.2.3.4
address@hidden example
+
 @item -net vde[,address@hidden,address@hidden,address@hidden 
[,address@hidden,address@hidden,address@hidden
 Connect VLAN @var{n} to PORT @var{n} of a vde switch running on host and
 listening for incoming connections on @var{socketpath}. Use GROUP 
@var{groupname}
-- 
1.7.0.4




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