xen: do not use ioemu type for any emulated NIC

When using the xm/xend stack to manage instances there is a bug
that causes the emulated interfaces to be unusable when the vif
config contains type=ioemu.

The current code already has a special quirk to not use this
keyword if no specific model is given for the emulated NIC
(defaulting to rtl8139).
Essentially it works because regardless of the type argument,i
the Xen stack always creates emulated and paravirt interfaces and
lets the guest decide which one to use. So neither xl nor xm stack
actually require the type keyword for emulated NICs.
Signed-off-by: NStefan Bader <stefan.bader@canonical.com>

src/xenxs/xen_sxpr.c

@@ -1999,20 +1999,22 @@ xenFormatSxprNet(virConnectPtr conn,
         if (def->model != NULL)
             virBufferEscapeSexpr(buf, "(model '%s')", def->model);
     }
-    else if (def->model == NULL) {
-        /*
-         * apparently (type ioemu) breaks paravirt drivers on HVM so skip
-         * this from XEND_CONFIG_MAX_VERS_NET_TYPE_IOEMU
-         */
-        if (xendConfigVersion <= XEND_CONFIG_MAX_VERS_NET_TYPE_IOEMU)
-            virBufferAddLit(buf, "(type ioemu)");
-    }
-    else if (STREQ(def->model, "netfront")) {
-        virBufferAddLit(buf, "(type netfront)");
-    }
     else {
-        virBufferEscapeSexpr(buf, "(model '%s')", def->model);
-        virBufferAddLit(buf, "(type ioemu)");
+        if (def->model != NULL && STREQ(def->model, "netfront")) {
+            virBufferAddLit(buf, "(type netfront)");
+        }
+        else {
+            if (def->model != NULL) {
+                virBufferEscapeSexpr(buf, "(model '%s')", def->model);
+            }
+            /*
+             * apparently (type ioemu) breaks paravirt drivers on HVM so skip
+             * this from XEND_CONFIG_MAX_VERS_NET_TYPE_IOEMU
+             */
+            if (xendConfigVersion <= XEND_CONFIG_MAX_VERS_NET_TYPE_IOEMU) {
+                virBufferAddLit(buf, "(type ioemu)");
+            }
+        }
     }
 
     if (!isAttach)

src/xenxs/xen_xm.c

@@ -1381,20 +1381,21 @@ static int xenFormatXMNet(virConnectPtr conn,
         if (net->model != NULL)
             virBufferAsprintf(&buf, ",model=%s", net->model);
     }
-    else if (net->model == NULL) {
-        /*
-         * apparently type ioemu breaks paravirt drivers on HVM so skip this
-         * from XEND_CONFIG_MAX_VERS_NET_TYPE_IOEMU
-         */
-        if (xendConfigVersion <= XEND_CONFIG_MAX_VERS_NET_TYPE_IOEMU)
-            virBufferAddLit(&buf, ",type=ioemu");
-    }
-    else if (STREQ(net->model, "netfront")) {
-        virBufferAddLit(&buf, ",type=netfront");
-    }
     else {
-        virBufferAsprintf(&buf, ",model=%s", net->model);
-        virBufferAddLit(&buf, ",type=ioemu");
+        if (net->model != NULL && STREQ(net->model, "netfront")) {
+            virBufferAddLit(&buf, ",type=netfront");
+        }
+        else {
+            if (net->model != NULL)
+                virBufferAsprintf(&buf, ",model=%s", net->model);
+
+            /*
+             * apparently type ioemu breaks paravirt drivers on HVM so skip this
+             * from XEND_CONFIG_MAX_VERS_NET_TYPE_IOEMU
+             */
+            if (xendConfigVersion <= XEND_CONFIG_MAX_VERS_NET_TYPE_IOEMU)
+                virBufferAddLit(&buf, ",type=ioemu");
+        }
     }
 
     if (net->ifname)