[Qemu-devel] Re: [PATCH] add a command line option to specify the interface to send multicast packets on

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 10, 2010 at 05:47:35PM -0800, Mike Ryan wrote:
> Add an option to specify the host interface to send multicast packets on
> when using a multicast socket for networking. The option takes the name
> of a host interface (e.g., eth0) and sets the IP_MULTICAST_IF socket
> option, which causes the packets to use that interface as an egress.
> 
> This is useful if the host machine has several interfaces with several
> virtual networks across disparate interfaces.
> @@ -201,6 +203,23 @@ static int net_socket_mcast_create(struct sockaddr_in *mcastaddr)
>  	goto fail;
>      }
>  
> +    /* If an interface name is given, only send packets out that interface */
> +    if (interface != NULL) {
> +        strncpy(ifr.ifr_name, interface, IFNAMSIZ);
> +        ret = ioctl(fd, SIOCGIFADDR, &ifr);
> +        if (ret < 0) {
> +            fprintf(stderr, "qemu: error: specified interface \"%s\" does not exist\n", interface);
> +            goto fail;
> +        }
> +
> +        maddr = ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr;
> +        ret = setsockopt(fd, IPPROTO_IP, IP_MULTICAST_IF, &maddr, sizeof(maddr));
> +        if (ret < 0) {
> +            perror("setsockopt(IP_MULTICAST_IF)");
> +            goto fail;
> +        }

Let's let the user pass in the IP address? That would solve the
portability issue. Further, we could be doing IPv6, right?
So you'd need IPV6_MULTICAST_IF?
Also - you might also want to control
IP_MULTICAST_LOOP/IPV6_MULTICAST_LOOP?

> +    }
> +
>      socket_set_nonblock(fd);
>      return fd;
>  fail:
> @@ -248,7 +267,7 @@ 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);
> @@ -468,7 +487,8 @@ 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 *interface)
>  {
>      NetSocketState *s;
>      int fd;
> @@ -478,7 +498,7 @@ static int net_socket_mcast_init(VLANState *vlan,
>          return -1;
>  
>  
> -    fd = net_socket_mcast_create(&saddr);
> +    fd = net_socket_mcast_create(&saddr, interface);
>      if (fd < 0)
>  	return -1;
>  
> @@ -505,8 +525,9 @@ 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, "interface")) {
> +            error_report("listen=, connect=, mcast= and interface= is invalid with fd=\n");
>              return -1;
>          }
>  
> @@ -524,8 +545,9 @@ 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, "interface")) {
> +            error_report("fd=, connect=, mcast= and interface= is invalid with listen=\n");
>              return -1;
>          }
>  
> @@ -539,8 +561,9 @@ 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, "interface")) {
> +            error_report("fd=, listen=, mcast= and interface= is invalid with connect=\n");
>              return -1;
>          }
>  
> @@ -550,7 +573,7 @@ int net_init_socket(QemuOpts *opts,
>              return -1;
>          }
>      } else if (qemu_opt_get(opts, "mcast")) {
> -        const char *mcast;
> +        const char *mcast, *interface;
>  
>          if (qemu_opt_get(opts, "fd") ||
>              qemu_opt_get(opts, "connect") ||
> @@ -560,8 +583,9 @@ int net_init_socket(QemuOpts *opts,
>          }
>  
>          mcast = qemu_opt_get(opts, "mcast");
> +        interface = qemu_opt_get(opts, "interface");
>  
> -        if (net_socket_mcast_init(vlan, "socket", name, mcast) == -1) {
> +        if (net_socket_mcast_init(vlan, "socket", name, mcast, interface) == -1) {
>              return -1;
>          }
>      } else {
> diff --git a/qemu-common.h b/qemu-common.h
> index b3957f1..e8bc4af 100644
> --- a/qemu-common.h
> +++ b/qemu-common.h
> @@ -34,6 +34,7 @@ typedef struct DeviceState DeviceState;
>  #include <fcntl.h>
>  #include <sys/stat.h>
>  #include <assert.h>
> +#include <sys/ioctl.h>
>  
>  #ifndef O_LARGEFILE
>  #define O_LARGEFILE 0
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 4d99a58..e2c4cfa 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[,interface=ifname]]\n"
>      "                connect the vlan 'n' to multicast maddr and port\n"
> +    "                use 'interface=ifname' to specify the host interface to send packets on\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
>  
> -@item -net socket[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}] [,mcast=@var{maddr}:@var{port}]
> +@item -net socket[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,mcast=@var{maddr}:@var{port}[,interface=@var{ifname}]]
>  
>  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 on host's eth0):
> +@example
> +qemu linux.img -net nic,macaddr=52:54:00:12:34:56 \
> +               -net socket,mcast=239.192.168.1:1102,interface=eth0
> +@end example
> +
>  @item -net vde[,vlan=@var{n}][,name=@var{name}][,sock=@var{socketpath}] [,port=@var{n}][,group=@var{groupname}][,mode=@var{octalmode}]
>  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}
> diff --git a/qemu_socket.h b/qemu_socket.h
> index 897a8ae..5116e4a 100644
> --- a/qemu_socket.h
> +++ b/qemu_socket.h
> @@ -24,6 +24,7 @@ int inet_aton(const char *cp, struct in_addr *ia);
>  #include <arpa/inet.h>
>  #include <netdb.h>
>  #include <sys/un.h>
> +#include <net/if.h>
>  
>  #define socket_error() errno
>  #define closesocket(s) close(s)
> -- 
> 1.7.0.4
>