net: Allow hubports to connect to other netdevs

QEMU can emulate hubs to connect NICs and netdevs. This is currently
primarily used for the mis-named 'vlan' feature of the networking
subsystem. Now the 'vlan' feature has been marked as deprecated, since
its name is rather confusing and the users often rather mis-configure
their network when trying to use it. But while the 'vlan' parameter
should be removed at one point in time, the basic idea of emulating
a hub in QEMU is still good: It's useful for bundling up the output of
multiple NICs into one single l2tp netdev for example.

Now to be able to use the hubport feature without 'vlan's, there is one
missing piece: The possibility to connect a hubport to a netdev, too.
This patch adds this possibility by introducing a new "netdev=..."
parameter to the hubports.

To bundle up the output of multiple NICs into one socket netdev, you can
now run QEMU with these parameters for example:

qemu-system-ppc64 ... -netdev socket,id=s1,connect=:11122 \
    -netdev hubport,hubid=1,id=h1,netdev=s1 \
    -netdev hubport,hubid=1,id=h2 -device e1000,netdev=h2 \
    -netdev hubport,hubid=1,id=h3 -device virtio-net-pci,netdev=h3

For using the socket netdev, you have got to start another QEMU as the
receiving side first, for example with network dumping enabled:

qemu-system-x86_64 -M isapc -netdev socket,id=s0,listen=:11122 \
    -device ne2k_isa,netdev=s0 \
    -object filter-dump,id=f1,netdev=s0,file=/tmp/dump.dat

After the ppc64 guest tried to boot from both NICs, you can see in the
dump file (using Wireshark, for example), that the output of both NICs
(the e1000 and the virtio-net-pci) has been successfully transfered
via the socket netdev in this case.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

5 files changed, 32 insertions, 12 deletions

diff --git a/net/hub.c b/net/hub.c
index 14b4eec68f..5e84a9ad93 100644
--- a/net/hub.c
+++ b/net/hub.c
@@ -13,6 +13,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qapi/error.h"
 #include "monitor/monitor.h"
 #include "net/net.h"
 #include "clients.h"
@@ -140,7 +141,8 @@ static NetClientInfo net_hub_port_info = {
     .cleanup = net_hub_port_cleanup,
 };
 
-static NetHubPort *net_hub_port_new(NetHub *hub, const char *name)
+static NetHubPort *net_hub_port_new(NetHub *hub, const char *name,
+                                    NetClientState *hubpeer)
 {
     NetClientState *nc;
     NetHubPort *port;
@@ -153,7 +155,7 @@ static NetHubPort *net_hub_port_new(NetHub *hub, const char *name)
         name = default_name;
     }
 
-    nc = qemu_new_net_client(&net_hub_port_info, NULL, "hub", name);
+    nc = qemu_new_net_client(&net_hub_port_info, hubpeer, "hub", name);
     port = DO_UPCAST(NetHubPort, nc, nc);
     port->id = id;
     port->hub = hub;
@@ -165,11 +167,14 @@ static NetHubPort *net_hub_port_new(NetHub *hub, const char *name)
 
 /**
  * Create a port on a given hub
+ * @hub_id: Number of the hub
  * @name: Net client name or NULL for default name.
+ * @hubpeer: Peer to use (if "netdev=id" has been specified)
  *
  * If there is no existing hub with the given id then a new hub is created.
  */
-NetClientState *net_hub_add_port(int hub_id, const char *name)
+NetClientState *net_hub_add_port(int hub_id, const char *name,
+                                 NetClientState *hubpeer)
 {
     NetHub *hub;
     NetHubPort *port;
@@ -184,7 +189,7 @@ NetClientState *net_hub_add_port(int hub_id, const char *name)
         hub = net_hub_new(hub_id);
     }
 
-    port = net_hub_port_new(hub, name);
+    port = net_hub_port_new(hub, name, hubpeer);
     return &port->nc;
 }
 
@@ -232,7 +237,7 @@ NetClientState *net_hub_port_find(int hub_id)
         }
     }
 
-    nc = net_hub_add_port(hub_id, NULL);
+    nc = net_hub_add_port(hub_id, NULL, NULL);
     return nc;
 }
 
@@ -286,12 +291,22 @@ int net_init_hubport(const Netdev *netdev, const char *name,
                      NetClientState *peer, Error **errp)
 {
     const NetdevHubPortOptions *hubport;
+    NetClientState *hubpeer = NULL;
 
     assert(netdev->type == NET_CLIENT_DRIVER_HUBPORT);
     assert(!peer);
     hubport = &netdev->u.hubport;
 
-    net_hub_add_port(hubport->hubid, name);
+    if (hubport->has_netdev) {
+        hubpeer = qemu_find_netdev(hubport->netdev);
+        if (!hubpeer) {
+            error_setg(errp, "netdev '%s' not found", hubport->netdev);
+            return -1;
+        }
+    }
+
+    net_hub_add_port(hubport->hubid, name, hubpeer);
+
     return 0;
 }
 
diff --git a/net/hub.h b/net/hub.h
index a625effe00..6a16f0487a 100644
--- a/net/hub.h
+++ b/net/hub.h
@@ -17,7 +17,8 @@
 
 #include "qemu-common.h"
 
-NetClientState *net_hub_add_port(int hub_id, const char *name);
+NetClientState *net_hub_add_port(int hub_id, const char *name,
+                                 NetClientState *hubpeer);
 NetClientState *net_hub_find_client_by_name(int hub_id, const char *name);
 void net_hub_info(Monitor *mon);
 void net_hub_check_clients(void);
diff --git a/net/net.c b/net/net.c
index 2b81c93193..e1569e7d89 100644
--- a/net/net.c
+++ b/net/net.c
@@ -1063,7 +1063,7 @@ static int net_client_init1(const void *object, bool is_netdev, Error **errp)
         /* Do not add to a vlan if it's a nic with a netdev= parameter. */
         if (netdev->type != NET_CLIENT_DRIVER_NIC ||
             !opts->u.nic.has_netdev) {
-            peer = net_hub_add_port(net->has_vlan ? net->vlan : 0, NULL);
+            peer = net_hub_add_port(net->has_vlan ? net->vlan : 0, NULL, NULL);
         }
 
         if (net->has_vlan && !vlan_warned) {
diff --git a/qapi/net.json b/qapi/net.json
index 4beff5d582..1238ba5de1 100644
--- a/qapi/net.json
+++ b/qapi/net.json
@@ -410,12 +410,14 @@
 # Connect two or more net clients through a software hub.
 #
 # @hubid: hub identifier number
+# @netdev: used to connect hub to a netdev instead of a device (since 2.12)
 #
 # Since: 1.2
 ##
 { 'struct': 'NetdevHubPortOptions',
   'data': {
-    'hubid':     'int32' } }
+    'hubid':     'int32',
+    '*netdev':    'str' } }
 
 ##
 # @NetdevNetmapOptions:
diff --git a/qemu-options.hx b/qemu-options.hx
index 1d73fb151d..56b9a8692e 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2000,7 +2000,7 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
 #endif
     "-netdev vhost-user,id=str,chardev=dev[,vhostforce=on|off]\n"
     "                configure a vhost-user network, backed by a chardev 'dev'\n"
-    "-netdev hubport,id=str,hubid=n\n"
+    "-netdev hubport,id=str,hubid=n[,netdev=nd]\n"
     "                configure a hub port on QEMU VLAN 'n'\n", QEMU_ARCH_ALL)
 DEF("net", HAS_ARG, QEMU_OPTION_net,
     "-net nic[,vlan=n][,netdev=nd][,macaddr=mac][,model=type][,name=str][,addr=str][,vectors=v]\n"
@@ -2428,13 +2428,15 @@ vde_switch -F -sock /tmp/myswitch
 qemu-system-i386 linux.img -net nic -net vde,sock=/tmp/myswitch
 @end example
 
-@item -netdev hubport,id=@var{id},hubid=@var{hubid}
+@item -netdev hubport,id=@var{id},hubid=@var{hubid}[,netdev=@var{nd}]
 
 Create a hub port on QEMU "vlan" @var{hubid}.
 
 The hubport netdev lets you connect a NIC to a QEMU "vlan" instead of a single
 netdev.  @code{-net} and @code{-device} with parameter @option{vlan} create the
-required hub automatically.
+required hub automatically. Alternatively, you can also connect the hubport
+to another netdev with ID @var{nd} by using the @option{netdev=@var{nd}}
+option.
 
 @item -netdev vhost-user,chardev=@var{id}[,vhostforce=on|off][,queues=n]