[libvirt] Using Libvirt to change the bridge a virtual network card of a running vm is connected to

[Hendrik Schwartke]

I wrote a patch to change the mapping between a virtual bridge interface 
and the host bridge while the host is up. It's based on commit 
6fba577e505611e6c25c68e322942eab7754de7e. The host and the interface 
definition I used for testing are also attached.
I would be glad if the patch could be added to the repo.

Patch:

diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
index 4b60839..f791795 100644
--- a/src/qemu/qemu_hotplug.c
+++ b/src/qemu/qemu_hotplug.c
@@ -40,6 +40,7 @@
  #include "qemu_cgroup.h"
  #include "locking/domain_lock.h"
  #include "network/bridge_driver.h"
+#include "util/virnetdevbridge.h"

  #define VIR_FROM_THIS VIR_FROM_QEMU

@@ -1163,6 +1164,28 @@ static virDomainNetDefPtr 
qemuDomainFindNet(virDomainObjPtr vm,
      return NULL;
  }

+int qemuDomainChangeNetBridge(virDomainNetDefPtr olddev,
+                              virDomainNetDefPtr newdev)
+{
+    const char *oldbridge=olddev->data.bridge.brname;
+    const char *newbridge=newdev->data.bridge.brname;
+    VIR_DEBUG("Change bridge for interface %s: %s -> %s", 
olddev->ifname, oldbridge, newbridge);
+    if(virNetDevBridgeRemovePort(oldbridge, olddev->ifname)<0) {
+        qemuReportError(VIR_ERR_OPERATION_FAILED,
+                        _("unable to remove port from bridge"));
+        return -1;
+    }
+    if(virNetDevBridgeAddPort(newbridge, newdev->ifname)<0) {
+        qemuReportError(VIR_ERR_OPERATION_FAILED,
+                        _("unable to add port to bridge"));
+        return -1;
+    }
+    VIR_FREE(olddev->data.bridge.brname);
+    olddev->data.bridge.brname=strdup(newbridge);
+    return 0;
+}
+
+
  int qemuDomainChangeNetLinkState(struct qemud_driver *driver,
                                   virDomainObjPtr vm,
                                   virDomainNetDefPtr dev,
@@ -1293,6 +1316,12 @@ int qemuDomainChangeNet(struct qemud_driver *driver,
          return -1;
      }

+    if(olddev->type==VIR_DOMAIN_NET_TYPE_BRIDGE
+ && dev->type==VIR_DOMAIN_NET_TYPE_BRIDGE
+ && STRNEQ(olddev->data.bridge.brname, dev->data.bridge.brname)) {
+        qemuDomainChangeNetBridge(olddev, dev);
+    }
+
      if (olddev->linkstate != dev->linkstate) {
          if ((ret = qemuDomainChangeNetLinkState(driver, vm, olddev, 
dev->linkstate)) < 0)
              return ret;
diff --git a/src/qemu/qemu_hotplug.h b/src/qemu/qemu_hotplug.h
index 0310361..1e1f75c 100644
--- a/src/qemu/qemu_hotplug.h
+++ b/src/qemu/qemu_hotplug.h
@@ -80,6 +80,8 @@ int qemuDomainChangeNetLinkState(struct qemud_driver 
*driver,
                                   virDomainObjPtr vm,
                                   virDomainNetDefPtr dev,
                                   int linkstate);
+int qemuDomainChangeNetBridge(virDomainNetDefPtr olddev,
+                              virDomainNetDefPtr newdev);
  int qemuDomainDetachPciDiskDevice(struct qemud_driver *driver,
                                    virDomainObjPtr vm,
                                    virDomainDeviceDefPtr dev);


Host definition:
<domain type='kvm'>
<name>test</name>
<memory>32768</memory>
<currentMemory>32768</currentMemory>
<vcpu>1</vcpu>
<os>
<type arch='x86_64' machine='pc-0.12'>hvm</type>
<boot dev='cdrom'/>
<bootmenu enable='no'/>
</os>
<features>
<acpi/>
<apic/>
<pae/>
</features>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<devices>
<emulator>/usr/bin/kvm</emulator>
<controller type='ide' index='0'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
</controller>
<interface type='bridge'>
<mac address='52:54:00:ab:cd:02'/>
<source bridge='br0'/>
<target dev='testif'/>
<link state='up'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
<serial type='pty'>
<target port='0'/>
</serial>
<console type='pty'>
<target type='serial' port='0'/>
</console>
<input type='tablet' bus='usb'/>
<input type='mouse' bus='ps2'/>
<graphics type='vnc' port='-1' autoport='yes'/>
<video>
<model type='cirrus' vram='9216' heads='1'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
</video>
<memballoon model='virtio'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
</memballoon>
</devices>
</domain>


Interface definition:
<interface type="bridge">
<mac address="52:54:00:ab:cd:02"/>
<source bridge="br1"/>
<target dev="testif"/>
<link state="up"/>
<alias name="net0"/>
<address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x0"/>
</interface>



Best regards
Hendrik Schwartke