qemu: Don't remove macvtaps on failed start

If a domain is configured to create a macvtap/macvlan but the
target link already exists, startup fails (as expected) with:

  error: error creating macvtap interface test@eth0 (52:54:00:d9:0b:db): File exists

Okay, we could make that error message better, but that's not the
point. Since this error originated while generating cmd line
(the caller is qemuProcessStart(), transitively), the cleanup
after failed start is performed (qemuProcessStop()). Here,
virNetDevMacVLanDeleteWithVPortProfile() is called which removes
the macvtap interface we did not create (as it made us fail in
the first place).

Therefore, we need to track which macvtap/macvlan interface was
created successfully and remove only those.

You'll notice that only qemuProcessStop() has the new check. For
the (failed) hotplug case (qemuDomainAttachNetDevice()) this
function is already in place (the @iface_connected variable), or
not needed (qemuDomainRemoveNetDevice() - we're removing an
interface that was already attached to QEMU).

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2166235
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_domain.c

@@ -1235,6 +1235,31 @@ qemuDomainTPMPrivateFormat(const virDomainTPMDef *tpm,
 }
 
 
+static int
+qemuDomainNetworkPrivateParse(xmlXPathContextPtr ctxt,
+                              virDomainNetDef *net)
+{
+    qemuDomainNetworkPrivate *priv = QEMU_DOMAIN_NETWORK_PRIVATE(net);
+
+    priv->created = virXPathBoolean("string(./created[@value='yes'])", ctxt);
+
+    return 0;
+}
+
+
+static int
+qemuDomainNetworkPrivateFormat(const virDomainNetDef *net,
+                               virBuffer *buf)
+{
+    qemuDomainNetworkPrivate *priv = QEMU_DOMAIN_NETWORK_PRIVATE(net);
+
+    if (priv->created)
+        virBufferAddLit(buf, "<created value='yes'/>\n");
+
+    return 0;
+}
+
+
 /* qemuDomainSecretInfoSetup:
  * @priv: pointer to domain private object
  * @alias: alias of the secret
@@ -3328,6 +3353,8 @@ virDomainXMLPrivateDataCallbacks virQEMUDriverPrivateDataCallbacks = {
     .vsockNew = qemuDomainVsockPrivateNew,
     .graphicsNew = qemuDomainGraphicsPrivateNew,
     .networkNew = qemuDomainNetworkPrivateNew,
+    .networkParse = qemuDomainNetworkPrivateParse,
+    .networkFormat = qemuDomainNetworkPrivateFormat,
     .videoNew = qemuDomainVideoPrivateNew,
     .tpmNew = qemuDomainTPMPrivateNew,
     .tpmParse = qemuDomainTPMPrivateParse,

src/qemu/qemu_domain.h

@@ -412,6 +412,11 @@ typedef struct _qemuDomainNetworkPrivate qemuDomainNetworkPrivate;
 struct _qemuDomainNetworkPrivate {
     virObject parent;
 
+    /* True if the device was created by us. Otherwise we should
+     * avoid removing it. Currently only used for
+     * VIR_DOMAIN_NET_TYPE_DIRECT. */
+    bool created;
+
     qemuSlirp *slirp;
 
     /* file descriptor transfer helpers */

src/qemu/qemu_interface.c

@@ -268,6 +268,7 @@ qemuInterfaceDirectConnect(virDomainDef *def,
     char *res_ifname = NULL;
     g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(driver);
     unsigned int macvlan_create_flags = VIR_NETDEV_MACVLAN_CREATE_WITH_TAP;
+    qemuDomainNetworkPrivate *netpriv = QEMU_DOMAIN_NETWORK_PRIVATE(net);
 
     if (qemuInterfaceIsVnetCompatModel(net))
         macvlan_create_flags |= VIR_NETDEV_MACVLAN_VNET_HDR;
@@ -285,6 +286,8 @@ qemuInterfaceDirectConnect(virDomainDef *def,
                                                macvlan_create_flags) < 0)
         goto cleanup;
 
+    netpriv->created = true;
+
     virDomainAuditNetDevice(def, net, res_ifname, true);
     VIR_FREE(net->ifname);
     net->ifname = res_ifname;

src/qemu/qemu_process.c

@@ -8443,11 +8443,13 @@ void qemuProcessStop(virQEMUDriver *driver,
         vport = virDomainNetGetActualVirtPortProfile(net);
         switch (virDomainNetGetActualType(net)) {
         case VIR_DOMAIN_NET_TYPE_DIRECT:
-            virNetDevMacVLanDeleteWithVPortProfile(net->ifname, &net->mac,
-                                                   virDomainNetGetActualDirectDev(net),
-                                                   virDomainNetGetActualDirectMode(net),
-                                                   virDomainNetGetActualVirtPortProfile(net),
-                                                   cfg->stateDir);
+            if (QEMU_DOMAIN_NETWORK_PRIVATE(net)->created) {
+                virNetDevMacVLanDeleteWithVPortProfile(net->ifname, &net->mac,
+                                                       virDomainNetGetActualDirectDev(net),
+                                                       virDomainNetGetActualDirectMode(net),
+                                                       virDomainNetGetActualVirtPortProfile(net),
+                                                       cfg->stateDir);
+            }
             break;
         case VIR_DOMAIN_NET_TYPE_ETHERNET:
             if (net->managed_tap != VIR_TRISTATE_BOOL_NO && net->ifname) {