Patchwork add a command line option to specify the interface to send multicast packets on

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Submitter Mike Ryan
Date Nov. 11, 2010, 1:47 a.m.
Message ID <20101111014735.GQ2211@zzz.isi.edu>
Download mbox | patch
Permalink /patch/70749/
State New
Headers show

Comments

Mike Ryan - Nov. 11, 2010, 1:47 a.m.
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.
---
 net.c           |    4 ++++
 net/socket.c    |   48 ++++++++++++++++++++++++++++++++++++------------
 qemu-common.h   |    1 +
 qemu-options.hx |   11 +++++++++--
 qemu_socket.h   |    1 +
 5 files changed, 51 insertions(+), 14 deletions(-)
Mike Ryan - Nov. 15, 2010, 6:54 p.m.
Anyone care to comment?

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.
> ---
>  net.c           |    4 ++++
>  net/socket.c    |   48 ++++++++++++++++++++++++++++++++++++------------
>  qemu-common.h   |    1 +
>  qemu-options.hx |   11 +++++++++--
>  qemu_socket.h   |    1 +
>  5 files changed, 51 insertions(+), 14 deletions(-)
> 
> diff --git a/net.c b/net.c
> index c5e6063..ff9eb27 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 = "interface",
> +                .type = QEMU_OPT_STRING,
> +                .help = "interface to send multicast packets on",
>              },
>              { /* end of list */ }
>          },
> diff --git a/net/socket.c b/net/socket.c
> index 1c4e153..ed7cd12 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -149,11 +149,13 @@ 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, const char *interface)
>  {
>      struct ip_mreq imr;
>      int fd;
>      int val, ret;
> +    struct in_addr maddr;
> +    struct ifreq ifr;
>      if (!IN_MULTICAST(ntohl(mcastaddr->sin_addr.s_addr))) {
>  	fprintf(stderr, "qemu: error: specified mcastaddr \"%s\" (0x%08x) does not contain a multicast address\n",
>  		inet_ntoa(mcastaddr->sin_addr),
> @@ -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;
> +        }
> +    }
> +
>      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
>
Anthony Liguori - Nov. 15, 2010, 7:36 p.m.
On 11/15/2010 12:54 PM, Mike Ryan wrote:
> Anyone care to comment?
>    

I must admit, I don't understand the use-case well enough to really give 
an appropriate amount of review as to whether this is the best solution 
to the problem.

Michael, do you have any thoughts?

Regards,

Anthony Liguori

> 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.
>> ---
>>   net.c           |    4 ++++
>>   net/socket.c    |   48 ++++++++++++++++++++++++++++++++++++------------
>>   qemu-common.h   |    1 +
>>   qemu-options.hx |   11 +++++++++--
>>   qemu_socket.h   |    1 +
>>   5 files changed, 51 insertions(+), 14 deletions(-)
>>
>> diff --git a/net.c b/net.c
>> index c5e6063..ff9eb27 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 = "interface",
>> +                .type = QEMU_OPT_STRING,
>> +                .help = "interface to send multicast packets on",
>>               },
>>               { /* end of list */ }
>>           },
>> diff --git a/net/socket.c b/net/socket.c
>> index 1c4e153..ed7cd12 100644
>> --- a/net/socket.c
>> +++ b/net/socket.c
>> @@ -149,11 +149,13 @@ 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, const char *interface)
>>   {
>>       struct ip_mreq imr;
>>       int fd;
>>       int val, ret;
>> +    struct in_addr maddr;
>> +    struct ifreq ifr;
>>       if (!IN_MULTICAST(ntohl(mcastaddr->sin_addr.s_addr))) {
>>   	fprintf(stderr, "qemu: error: specified mcastaddr \"%s\" (0x%08x) does not contain a multicast address\n",
>>   		inet_ntoa(mcastaddr->sin_addr),
>> @@ -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;
>> +        }
>> +    }
>> +
>>       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
>>
>>      
>
Mike Ryan - Nov. 15, 2010, 7:52 p.m.
I'll clarify/elaborate a bit:

When using a multicast socket, the OS chooses a default physical
interface to send packets. The patch I've supplied allows the user to
select the interface.

Suppose you have a setup like so:

BoxA --- BoxB --- BoxC

You wish to run virtual machines on BoxB and BoxC and network them using
a multicast UDP socket.

BoxB has two network interfaces, and the default multicast interface may
be the link between BoxA and BoxB. In this situation, BoxC will not
receive any multicast packets from BoxB and networking between the boxes
is therefore impossible.

The utility of a multicast socket is obviously limited in my simplified
example. Generalize BoxC to a LAN of physical machines all running
virtual machines you wish to network and the use case should become a
bit clearer.

On Mon, Nov 15, 2010 at 01:36:28PM -0600, Anthony Liguori wrote:
> On 11/15/2010 12:54 PM, Mike Ryan wrote:
> >Anyone care to comment?
> 
> I must admit, I don't understand the use-case well enough to really
> give an appropriate amount of review as to whether this is the best
> solution to the problem.
> 
> Michael, do you have any thoughts?
> 
> Regards,
> 
> Anthony Liguori
> 
> >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.
> >>---
> >>  net.c           |    4 ++++
> >>  net/socket.c    |   48 ++++++++++++++++++++++++++++++++++++------------
> >>  qemu-common.h   |    1 +
> >>  qemu-options.hx |   11 +++++++++--
> >>  qemu_socket.h   |    1 +
> >>  5 files changed, 51 insertions(+), 14 deletions(-)
> >>
> >>diff --git a/net.c b/net.c
> >>index c5e6063..ff9eb27 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 = "interface",
> >>+                .type = QEMU_OPT_STRING,
> >>+                .help = "interface to send multicast packets on",
> >>              },
> >>              { /* end of list */ }
> >>          },
> >>diff --git a/net/socket.c b/net/socket.c
> >>index 1c4e153..ed7cd12 100644
> >>--- a/net/socket.c
> >>+++ b/net/socket.c
> >>@@ -149,11 +149,13 @@ 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, const char *interface)
> >>  {
> >>      struct ip_mreq imr;
> >>      int fd;
> >>      int val, ret;
> >>+    struct in_addr maddr;
> >>+    struct ifreq ifr;
> >>      if (!IN_MULTICAST(ntohl(mcastaddr->sin_addr.s_addr))) {
> >>  	fprintf(stderr, "qemu: error: specified mcastaddr \"%s\" (0x%08x) does not contain a multicast address\n",
> >>  		inet_ntoa(mcastaddr->sin_addr),
> >>@@ -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;
> >>+        }
> >>+    }
> >>+
> >>      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
> >>
>
Anthony Liguori - Nov. 15, 2010, 9:07 p.m.
On 11/15/2010 01:52 PM, Mike Ryan wrote:
> I'll clarify/elaborate a bit:
>
> When using a multicast socket, the OS chooses a default physical
> interface to send packets. The patch I've supplied allows the user to
> select the interface.
>
> Suppose you have a setup like so:
>
> BoxA --- BoxB --- BoxC
>
> You wish to run virtual machines on BoxB and BoxC and network them using
> a multicast UDP socket.
>
> BoxB has two network interfaces, and the default multicast interface may
> be the link between BoxA and BoxB. In this situation, BoxC will not
> receive any multicast packets from BoxB and networking between the boxes
> is therefore impossible.
>
> The utility of a multicast socket is obviously limited in my simplified
> example. Generalize BoxC to a LAN of physical machines all running
> virtual machines you wish to network and the use case should become a
> bit clearer.
>    

Thanks.  Second question is how portable is SIOCGIFADDR?  I suspect 
that's very Linux-centric..

Regards,

Anthony Liguori

> On Mon, Nov 15, 2010 at 01:36:28PM -0600, Anthony Liguori wrote:
>    
>> On 11/15/2010 12:54 PM, Mike Ryan wrote:
>>      
>>> Anyone care to comment?
>>>        
>> I must admit, I don't understand the use-case well enough to really
>> give an appropriate amount of review as to whether this is the best
>> solution to the problem.
>>
>> Michael, do you have any thoughts?
>>
>> Regards,
>>
>> Anthony Liguori
>>
>>      
>>> 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.
>>>> ---
>>>>   net.c           |    4 ++++
>>>>   net/socket.c    |   48 ++++++++++++++++++++++++++++++++++++------------
>>>>   qemu-common.h   |    1 +
>>>>   qemu-options.hx |   11 +++++++++--
>>>>   qemu_socket.h   |    1 +
>>>>   5 files changed, 51 insertions(+), 14 deletions(-)
>>>>
>>>> diff --git a/net.c b/net.c
>>>> index c5e6063..ff9eb27 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 = "interface",
>>>> +                .type = QEMU_OPT_STRING,
>>>> +                .help = "interface to send multicast packets on",
>>>>               },
>>>>               { /* end of list */ }
>>>>           },
>>>> diff --git a/net/socket.c b/net/socket.c
>>>> index 1c4e153..ed7cd12 100644
>>>> --- a/net/socket.c
>>>> +++ b/net/socket.c
>>>> @@ -149,11 +149,13 @@ 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, const char *interface)
>>>>   {
>>>>       struct ip_mreq imr;
>>>>       int fd;
>>>>       int val, ret;
>>>> +    struct in_addr maddr;
>>>> +    struct ifreq ifr;
>>>>       if (!IN_MULTICAST(ntohl(mcastaddr->sin_addr.s_addr))) {
>>>>   	fprintf(stderr, "qemu: error: specified mcastaddr \"%s\" (0x%08x) does not contain a multicast address\n",
>>>>   		inet_ntoa(mcastaddr->sin_addr),
>>>> @@ -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;
>>>> +        }
>>>> +    }
>>>> +
>>>>       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
>>>>
>>>>          
>>      
>
Stefan Weil - Nov. 15, 2010, 9:22 p.m.
Am 15.11.2010 22:07, schrieb Anthony Liguori:
> On 11/15/2010 01:52 PM, Mike Ryan wrote:
>> I'll clarify/elaborate a bit:
>>
>> When using a multicast socket, the OS chooses a default physical
>> interface to send packets. The patch I've supplied allows the user to
>> select the interface.
>>
>> Suppose you have a setup like so:
>>
>> BoxA --- BoxB --- BoxC
>>
>> You wish to run virtual machines on BoxB and BoxC and network them using
>> a multicast UDP socket.
>>
>> BoxB has two network interfaces, and the default multicast interface may
>> be the link between BoxA and BoxB. In this situation, BoxC will not
>> receive any multicast packets from BoxB and networking between the boxes
>> is therefore impossible.
>>
>> The utility of a multicast socket is obviously limited in my simplified
>> example. Generalize BoxC to a LAN of physical machines all running
>> virtual machines you wish to network and the use case should become a
>> bit clearer.
>
> Thanks.  Second question is how portable is SIOCGIFADDR?  I suspect 
> that's very Linux-centric..
>
> Regards,
>
> Anthony Liguori


Yes. It is unavailable for mingw32 (windows).

Regards,

Stefan Weil
Mike Ryan - Nov. 15, 2010, 9:34 p.m.
On Mon, Nov 15, 2010 at 03:07:51PM -0600, Anthony Liguori wrote:

<snip>

> Thanks.  Second question is how portable is SIOCGIFADDR?  I suspect
> that's very Linux-centric..

It ostensibly exists in FreeBSD, but I can't get master to compile under
7.3-RELEASE or 8.1-STABLE.

Given that it is unavailable on at least one platform (mingw32) it
sounds like it should be detected in configure. However configure
doesn't appear to be generated from autoconf/automake. Is it a custom
build system?
Paolo Bonzini - Nov. 16, 2010, 9:26 a.m.
On 11/15/2010 10:34 PM, Mike Ryan wrote:
> Given that it is unavailable on at least one platform (mingw32) it
> sounds like it should be detected in configure. However configure
> doesn't appear to be generated from autoconf/automake. Is it a custom
> build system?

Yes, but I think #ifndef _WIN32 is enough in this case, as it is what is 
used in the rest of QEMU for sys/ioctl.h stuff.

In Win32 you would use this: 
http://msdn.microsoft.com/en-us/library/aa365915%28v=VS.85%29.aspx

Paolo
Michael S. Tsirkin - Nov. 16, 2010, 5:54 p.m.
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
>
Mike Ryan - Nov. 16, 2010, 7:10 p.m.
On Tue, Nov 16, 2010 at 07:54:58PM +0200, Michael S. Tsirkin wrote:
>
> <snip>
>
> 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?

IP address seems like a good alternative and does indeed get rid of the
messy platform-specific bits.

The multicast code all assumes IPv4. For instance, it uses v4-only
parse_host_port to get the multicast destination address. Given that,
I'm not going to bother shoehorning in IPV6_MULTICAST_IF.

Patch

diff --git a/net.c b/net.c
index c5e6063..ff9eb27 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 = "interface",
+                .type = QEMU_OPT_STRING,
+                .help = "interface to send multicast packets on",
             },
             { /* end of list */ }
         },
diff --git a/net/socket.c b/net/socket.c
index 1c4e153..ed7cd12 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -149,11 +149,13 @@  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, const char *interface)
 {
     struct ip_mreq imr;
     int fd;
     int val, ret;
+    struct in_addr maddr;
+    struct ifreq ifr;
     if (!IN_MULTICAST(ntohl(mcastaddr->sin_addr.s_addr))) {
 	fprintf(stderr, "qemu: error: specified mcastaddr \"%s\" (0x%08x) does not contain a multicast address\n",
 		inet_ntoa(mcastaddr->sin_addr),
@@ -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;
+        }
+    }
+
     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)