[Qemu-devel] [PATCH] net: Allow hubports to connect to other netdevs

[Thomas Huth]

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 <address@hidden>
Signed-off-by: Thomas Huth <address@hidden>
---
 See also the original discussion here for some more information:
 https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg05650.html

 net/hub.c       | 23 ++++++++++++++++++++++-
 qapi/net.json   |  4 +++-
 qemu-options.hx |  8 +++++---
 3 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/net/hub.c b/net/hub.c
index 14b4eec..0638729 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"
@@ -286,12 +287,32 @@ int net_init_hubport(const Netdev *netdev, const char 
*name,
                      NetClientState *peer, Error **errp)
 {
     const NetdevHubPortOptions *hubport;
+    NetClientState *hubncs;
 
     assert(netdev->type == NET_CLIENT_DRIVER_HUBPORT);
     assert(!peer);
     hubport = &netdev->u.hubport;
 
-    net_hub_add_port(hubport->hubid, name);
+    hubncs = net_hub_add_port(hubport->hubid, name);
+    if (!hubncs) {
+        error_setg(errp, "failed to add port to hub %i with id '%s'",
+                   hubport->hubid, name);
+        return -1;
+    }
+
+    if (hubport->has_netdev) {
+        NetClientState *hubpeer;
+
+        hubpeer = qemu_find_netdev(hubport->netdev);
+        if (!hubpeer) {
+            error_setg(errp, "netdev '%s' not found", hubport->netdev);
+            return -1;
+        }
+        assert(!hubncs->peer && !hubpeer->peer);
+        hubncs->peer = hubpeer;
+        hubpeer->peer = hubncs;
+    }
+
     return 0;
 }
 
diff --git a/qapi/net.json b/qapi/net.json
index 4beff5d..e41e046 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 678181c..9ec4af7 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2017,7 +2017,7 @@ 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"
@@ -2445,13 +2445,15 @@ vde_switch -F -sock /tmp/myswitch
 qemu-system-i386 linux.img -net nic -net vde,sock=/tmp/myswitch
 @end example
 
address@hidden -netdev hubport,address@hidden,address@hidden
address@hidden -netdev hubport,address@hidden,address@hidden,address@hidden
 
 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 @address@hidden
+option.
 
 @item -netdev vhost-user,address@hidden,vhostforce=on|off][,queues=n]
 
-- 
1.8.3.1