net: add qemu_create_nic_bus_devices()

This will instantiate any NICs which live on a given bus type. Each bus
is allowed *one* substitution (for PCI it's virtio → virtio-net-pci, for
Xen it's xen → xen-net-device; no point in overengineering it unless we
actually want more).

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>

include/net/net.h

@@ -248,6 +248,28 @@ bool qemu_configure_nic_device(DeviceState *dev, bool match_default,
  */
 DeviceState *qemu_create_nic_device(const char *typename, bool match_default,
                                     const char *alias);
+
+/*
+ * qemu_create_nic_bus_devices: Create configured NIC devices for a given bus
+ * @bus: Bus on which to create devices
+ * @parent_type: Object type for devices to be created (e.g. TYPE_PCI_DEVICE)
+ * @default_model: Object type name for default NIC model (or %NULL)
+ * @alias: Additional model string to replace, for user convenience
+ * @alias_target: Actual object type name to be used in place of @alias
+ *
+ * Instantiate dynamic NICs on a given bus, typically a PCI bus. This scans
+ * for available NIC configurations which either specify a model which is
+ * a child type of @parent_type, or which do not specify a model when
+ * @default_model is non-NULL. Each device is instantiated on the given @bus.
+ *
+ * A single substitution is supported, e.g. "xen" → "xen-net-device" for the
+ * Xen bus, or "virtio" → "virtio-net-pci" for PCI. This allows the user to
+ * specify a more understandable "model=" parameter on the command line, not
+ * only the real object typename.
+ */
+void qemu_create_nic_bus_devices(BusState *bus, const char *parent_type,
+                                 const char *default_model,
+                                 const char *alias, const char *alias_target);
 void print_net_client(Monitor *mon, NetClientState *nc);
 void net_socket_rs_init(SocketReadState *rs,
                         SocketReadStateFinalize *finalize,

net/net.c

@@ -1223,6 +1223,59 @@ DeviceState *qemu_create_nic_device(const char *typename, bool match_default,
     return dev;
 }
 
+void qemu_create_nic_bus_devices(BusState *bus, const char *parent_type,
+                                 const char *default_model,
+                                 const char *alias, const char *alias_target)
+{
+    GPtrArray *nic_models = qemu_get_nic_models(parent_type);
+    const char *model;
+    DeviceState *dev;
+    NICInfo *nd;
+    int i;
+
+    if (nic_model_help) {
+        if (alias_target) {
+            add_nic_model_help(alias_target, alias);
+        }
+        for (i = 0; i < nic_models->len - 1; i++) {
+            add_nic_model_help(nic_models->pdata[i], NULL);
+        }
+    }
+
+    /* Drop the NULL terminator which would make g_str_equal() unhappy */
+    nic_models->len--;
+
+    for (i = 0; i < nb_nics; i++) {
+        nd = &nd_table[i];
+
+        if (!nd->used || nd->instantiated) {
+            continue;
+        }
+
+        model = nd->model ? nd->model : default_model;
+        if (!model) {
+            continue;
+        }
+
+        /* Each bus type is allowed *one* substitution */
+        if (g_str_equal(model, alias)) {
+            model = alias_target;
+        }
+
+        if (!g_ptr_array_find_with_equal_func(nic_models, model,
+                                              g_str_equal, NULL)) {
+            /* This NIC does not live on this bus. */
+            continue;
+        }
+
+        dev = qdev_new(model);
+        qdev_set_nic_properties(dev, nd);
+        qdev_realize_and_unref(dev, bus, &error_fatal);
+    }
+
+    g_ptr_array_free(nic_models, true);
+}
+
 static int (* const net_client_init_fun[NET_CLIENT_DRIVER__MAX])(
     const Netdev *netdev,
     const char *name,