[Libvir] PATCH: strip auto-generated VIF names from XML

[Daniel P. Berrange]

For the QEMU / KVM driver, if the user doesn't specify an explicit name for
the TAP device associated with a virtual NIC, we auto-generate one with a
name vnetXXX.  You can see this if you dump XML for a running QEMU guest.
Unfortunately if you dump XML, make a change and then feed it back in with
the define XML API, you have now persisted this auto-generated VIF name.

Do this for several domains at varying times and you'll eventually  get
2 domains which have persisted the same auto-generated vnetXXX device
name. You can now not start both of these VMs at once.

The fix for this is simple - simply strip any TAP device name starting with
the string 'vnet' when defining a new VM. It will thus get assigned a new
automatically generate name which doesn't clash. The patch also strips out
hardcoded vnetXXX names when starting a VM to proactively deal with any
existing VMs whose config has been broken in this way.

Dan.
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-------------- next part --------------
Index: src/qemu_conf.c
===================================================================
RCS file: /data/cvs/libvirt/src/qemu_conf.c,v
retrieving revision 1.21
diff -u -p -r1.21 qemu_conf.c
--- src/qemu_conf.c	3 Dec 2007 14:30:47 -0000	1.21
+++ src/qemu_conf.c	4 Dec 2007 16:56:42 -0000
@@ -657,6 +657,11 @@ static int qemudParseInterfaceXML(virCon
                         (net->type == QEMUD_NET_BRIDGE)) &&
                        xmlStrEqual(cur->name, BAD_CAST "target")) {
                 ifname = xmlGetProp(cur, BAD_CAST "dev");
+                if (STREQLEN("vnet", (const char*)ifname, 4)) {
+                    /* An auto-generated target name, blank it out */
+                    xmlFree(ifname);
+                    ifname = NULL;
+                }
             } else if ((script == NULL) &&
                        (net->type == QEMUD_NET_ETHERNET) &&
                        xmlStrEqual(cur->name, BAD_CAST "script")) {
@@ -1411,6 +1416,7 @@ qemudNetworkIfaceConnect(virConnectPtr c
         }
         brname = network->bridge;
         if (net->dst.network.ifname[0] == '\0' ||
+            STREQLEN(net->dst.network.ifname, "vnet", 4) ||
             strchr(net->dst.network.ifname, '%')) {
             strcpy(net->dst.network.ifname, "vnet%d");
         }
@@ -1418,6 +1424,7 @@ qemudNetworkIfaceConnect(virConnectPtr c
     } else if (net->type == QEMUD_NET_BRIDGE) {
         brname = net->dst.bridge.brname;
         if (net->dst.bridge.ifname[0] == '\0' ||
+            STREQLEN(net->dst.bridge.ifname, "vnet", 4) ||
             strchr(net->dst.bridge.ifname, '%')) {
             strcpy(net->dst.bridge.ifname, "vnet%d");
         }