qemu: Allow migration with host USB devices

Recently, patches were added support for (managed)saving, restoring, and
migrating domains with host USB devices. However, qemu driver would
still forbid migration of such domains because qemuMigrationIsAllowed
was not updated.

src/qemu/qemu_migration.c

@@ -800,6 +800,8 @@ qemuMigrationIsAllowed(struct qemud_driver *driver, virDomainObjPtr vm,
                        virDomainDefPtr def)
 {
     int nsnapshots;
+    bool forbid;
+    int i;
 
     if (vm) {
         if (qemuProcessAutoDestroyActive(driver, vm)) {
@@ -817,9 +819,23 @@ qemuMigrationIsAllowed(struct qemud_driver *driver, virDomainObjPtr vm,
 
         def = vm->def;
     }
-    if (def->nhostdevs > 0) {
-        virReportError(VIR_ERR_OPERATION_INVALID,
-                       "%s", _("Domain with assigned host devices cannot be migrated"));
+
+    /* Migration with USB host devices is allowed, all other devices are
+     * forbidden.
+     */
+    forbid = false;
+    for (i = 0; i < def->nhostdevs; i++) {
+        virDomainHostdevDefPtr hostdev = def->hostdevs[i];
+        if (hostdev->mode != VIR_DOMAIN_HOSTDEV_MODE_SUBSYS ||
+            hostdev->source.subsys.type != VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_USB) {
+            forbid = true;
+            break;
+        }
+    }
+    if (forbid) {
+        virReportError(VIR_ERR_OPERATION_INVALID, "%s",
+                       _("Domain with assigned non-USB host devices "
+                         "cannot be migrated"));
         return false;
     }