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Re: [Qemu-devel] [PATCH] add a command line option to specify the interf

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH] add a command line option to specify the interface to send multicast packets on
Date: Mon, 15 Nov 2010 15:07:51 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101027 Lightning/1.0b1 Thunderbird/3.0.10 
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

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 on host's eth0):
address@hidden
+qemu linux.img -net nic,macaddr=52:54:00:12:34:56 \
+               -net socket,mcast=239.192.168.1:1102,interface=eth0
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}
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
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