Re: [Qemu-devel] [PATCH] add a command line option to specify the IP address to send multicast packets from

[Mike Ryan <mikeryan@isi.edu>]

Michael, this patch implements the feature with a bind address instead
of a bind interface. It should address the cross-platform issues that
were raised.

Others: any comments?

On Wed, Nov 17, 2010 at 05:16:26PM -0800, Mike Ryan wrote:
> 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
>  
> -@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}[,localaddr=@var{addr}]]
>  
>  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):
> +@example
> +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
> +@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}
> -- 
> 1.7.0.4
>