qemu_hotplug: Support interface type of vhost-user hotplug

https://bugzilla.redhat.com/show_bug.cgi?id=1366108

There are couple of things that needs to be done in order to
allow vhost-user hotplug. Firstly, vhost-user requires a chardev
which is connected to vhost-user bridge and through which qemu
communicates with the bridge (no acutal guest traffic is sent
through there, just some metadata). In order to generate proper
chardev alias, we must assign device alias way sooner.

Then, because we are plugging the chardev first, we need to do
the proper undo if something fails - that is remove netdev too.
We don't want anything to be left over in case attach fails at
some point.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_hotplug.c

@@ -932,6 +932,10 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
     virDomainCCWAddressSetPtr ccwaddrs = NULL;
     size_t i;
+    char *charDevAlias = NULL;
+    bool charDevPlugged = false;
+    bool netdevPlugged = false;
+    bool hostPlugged = false;
 
     /* preallocate new slot for device */
     if (VIR_REALLOC_N(vm->def->nets, vm->def->nnets + 1) < 0)
@@ -970,6 +974,9 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
         return -1;
     }
 
+    if (qemuAssignDeviceNetAlias(vm->def, net, -1) < 0)
+        goto cleanup;
+
     switch (actualType) {
     case VIR_DOMAIN_NET_TYPE_BRIDGE:
     case VIR_DOMAIN_NET_TYPE_NETWORK:
@@ -1044,8 +1051,18 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
         goto cleanup;
         break;
 
-    case VIR_DOMAIN_NET_TYPE_USER:
     case VIR_DOMAIN_NET_TYPE_VHOSTUSER:
+        if (!qemuDomainSupportsNetdev(vm->def, priv->qemuCaps, net)) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           "%s", _("Netdev support unavailable"));
+            goto cleanup;
+        }
+
+        if (virAsprintf(&charDevAlias, "char%s", net->info.alias) < 0)
+            goto cleanup;
+        break;
+
+    case VIR_DOMAIN_NET_TYPE_USER:
     case VIR_DOMAIN_NET_TYPE_SERVER:
     case VIR_DOMAIN_NET_TYPE_CLIENT:
     case VIR_DOMAIN_NET_TYPE_MCAST:
@@ -1081,9 +1098,6 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
             goto cleanup;
     }
 
-    if (qemuAssignDeviceNetAlias(vm->def, net, -1) < 0)
-        goto cleanup;
-
     if (qemuDomainMachineIsS390CCW(vm->def) &&
         virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_VIRTIO_CCW)) {
         net->info.type = VIR_DOMAIN_DEVICE_ADDRESS_TYPE_CCW;
@@ -1143,23 +1157,36 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
     }
 
     qemuDomainObjEnterMonitor(driver, vm);
+
+    if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) {
+        if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) {
+            ignore_value(qemuDomainObjExitMonitor(driver, vm));
+            virDomainAuditNet(vm, NULL, net, "attach", false);
+            goto cleanup;
+        }
+        charDevPlugged = true;
+    }
+
     if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_NETDEV)) {
         if (qemuMonitorAddNetdev(priv->mon, netstr,
                                  tapfd, tapfdName, tapfdSize,
                                  vhostfd, vhostfdName, vhostfdSize) < 0) {
             ignore_value(qemuDomainObjExitMonitor(driver, vm));
             virDomainAuditNet(vm, NULL, net, "attach", false);
-            goto cleanup;
+            goto try_remove;
         }
+        netdevPlugged = true;
     } else {
         if (qemuMonitorAddHostNetwork(priv->mon, netstr,
                                       tapfd, tapfdName, tapfdSize,
                                       vhostfd, vhostfdName, vhostfdSize) < 0) {
             ignore_value(qemuDomainObjExitMonitor(driver, vm));
             virDomainAuditNet(vm, NULL, net, "attach", false);
-            goto cleanup;
+            goto try_remove;
         }
+        hostPlugged = true;
     }
+
     if (qemuDomainObjExitMonitor(driver, vm) < 0)
         goto cleanup;
 
@@ -1262,6 +1289,7 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
     }
     VIR_FREE(vhostfd);
     VIR_FREE(vhostfdName);
+    VIR_FREE(charDevAlias);
     virObjectUnref(cfg);
     virDomainCCWAddressSetFree(ccwaddrs);
 
@@ -1277,7 +1305,11 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
             if (virAsprintf(&netdev_name, "host%s", net->info.alias) < 0)
                 goto cleanup;
             qemuDomainObjEnterMonitor(driver, vm);
-            if (qemuMonitorRemoveNetdev(priv->mon, netdev_name) < 0)
+            if (charDevPlugged &&
+                qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0)
+                VIR_WARN("Failed to remove associated chardev %s", charDevAlias);
+            if (netdevPlugged &&
+                qemuMonitorRemoveNetdev(priv->mon, netdev_name) < 0)
                 VIR_WARN("Failed to remove network backend for netdev %s",
                          netdev_name);
             ignore_value(qemuDomainObjExitMonitor(driver, vm));
@@ -1290,7 +1322,8 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
         if (virAsprintf(&hostnet_name, "host%s", net->info.alias) < 0)
             goto cleanup;
         qemuDomainObjEnterMonitor(driver, vm);
-        if (qemuMonitorRemoveHostNetwork(priv->mon, vlan, hostnet_name) < 0)
+        if (hostPlugged &&
+            qemuMonitorRemoveHostNetwork(priv->mon, vlan, hostnet_name) < 0)
             VIR_WARN("Failed to remove network backend for vlan %d, net %s",
                      vlan, hostnet_name);
         ignore_value(qemuDomainObjExitMonitor(driver, vm));
@@ -3320,10 +3353,12 @@ qemuDomainRemoveNetDevice(virQEMUDriverPtr driver,
     virNetDevVPortProfilePtr vport;
     virObjectEventPtr event;
     char *hostnet_name = NULL;
+    char *charDevAlias = NULL;
     size_t i;
     int ret = -1;
+    int actualType = virDomainNetGetActualType(net);
 
-    if (virDomainNetGetActualType(net) == VIR_DOMAIN_NET_TYPE_HOSTDEV) {
+    if (actualType == VIR_DOMAIN_NET_TYPE_HOSTDEV) {
         /* this function handles all hostdev and netdev cleanup */
         ret = qemuDomainRemoveHostDevice(driver, vm,
                                          virDomainNetGetActualHostdev(net));
@@ -3333,9 +3368,11 @@ qemuDomainRemoveNetDevice(virQEMUDriverPtr driver,
     VIR_DEBUG("Removing network interface %s from domain %p %s",
               net->info.alias, vm, vm->def->name);
 
-    if (virAsprintf(&hostnet_name, "host%s", net->info.alias) < 0)
+    if (virAsprintf(&hostnet_name, "host%s", net->info.alias) < 0 ||
+        virAsprintf(&charDevAlias, "char%s", net->info.alias) < 0)
         goto cleanup;
 
+
     qemuDomainObjEnterMonitor(driver, vm);
     if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_NETDEV)) {
         if (qemuMonitorRemoveNetdev(priv->mon, hostnet_name) < 0) {
@@ -3358,6 +3395,17 @@ qemuDomainRemoveNetDevice(virQEMUDriverPtr driver,
             goto cleanup;
         }
     }
+
+    if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) {
+        /* vhostuser has a chardev too */
+        if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) {
+            /* well, this is a messy situation. Guest visible PCI device has
+             * been removed, netdev too but chardev not. The best seems to be
+             * to just ignore the error and carry on.
+             */
+        }
+    }
+
     if (qemuDomainObjExitMonitor(driver, vm) < 0)
         goto cleanup;
 
@@ -3382,7 +3430,7 @@ qemuDomainRemoveNetDevice(virQEMUDriverPtr driver,
                                                   &net->mac));
     }
 
-    if (virDomainNetGetActualType(net) == VIR_DOMAIN_NET_TYPE_DIRECT) {
+    if (actualType == VIR_DOMAIN_NET_TYPE_DIRECT) {
         ignore_value(virNetDevMacVLanDeleteWithVPortProfile(
                          net->ifname, &net->mac,
                          virDomainNetGetActualDirectDev(net),
@@ -3408,6 +3456,7 @@ qemuDomainRemoveNetDevice(virQEMUDriverPtr driver,
 
  cleanup:
     virObjectUnref(cfg);
+    VIR_FREE(charDevAlias);
     VIR_FREE(hostnet_name);
     return ret;
 }