net: stream: add QAPI events to report connection state

The netdev reports NETDEV_STREAM_CONNECTED event when the backend
is connected, and NETDEV_STREAM_DISCONNECTED when it is disconnected.

The NETDEV_STREAM_CONNECTED event includes the destination address.

This allows a system manager like libvirt to detect when the server
fails.

For instance with passt:

{ 'execute': 'qmp_capabilities' }
{ "return": { } }
{ "timestamp": { "seconds": 1666341395, "microseconds": 505347 },
    "event": "NETDEV_STREAM_CONNECTED",
    "data": { "netdev-id": "netdev0",
        "addr": { "path": "/tmp/passt_1.socket", "type": "unix" } } }

[killing passt here]

{ "timestamp": { "seconds": 1666341430, "microseconds": 968694 },
    "event": "NETDEV_STREAM_DISCONNECTED",
    "data": { "netdev-id": "netdev0" } }

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/stream.c

@@ -38,6 +38,7 @@
 #include "io/channel.h"
 #include "io/channel-socket.h"
 #include "io/net-listener.h"
+#include "qapi/qapi-events-net.h"
 
 typedef struct NetStreamState {
     NetClientState nc;
@@ -168,6 +169,8 @@ static gboolean net_stream_send(QIOChannel *ioc,
         s->nc.link_down = true;
         qemu_set_info_str(&s->nc, "");
 
+        qapi_event_send_netdev_stream_disconnected(s->nc.name);
+
         return G_SOURCE_REMOVE;
     }
     buf = buf1;
@@ -244,6 +247,7 @@ static void net_stream_listen(QIONetListener *listener,
     uri = socket_uri(addr);
     qemu_set_info_str(&s->nc, uri);
     g_free(uri);
+    qapi_event_send_netdev_stream_connected(s->nc.name, addr);
     qapi_free_SocketAddress(addr);
 }
 
@@ -335,6 +339,7 @@ static void net_stream_client_connected(QIOTask *task, gpointer opaque)
     s->ioc_read_tag = qio_channel_add_watch(s->ioc, G_IO_IN, net_stream_send,
                                             s, NULL);
     s->nc.link_down = false;
+    qapi_event_send_netdev_stream_connected(s->nc.name, addr);
     qapi_free_SocketAddress(addr);
 
     return;

qapi/net.json

@@ -898,3 +898,52 @@
 ##
 { 'event': 'FAILOVER_NEGOTIATED',
   'data': {'device-id': 'str'} }
+
+##
+# @NETDEV_STREAM_CONNECTED:
+#
+# Emitted when the netdev stream backend is connected
+#
+# @netdev-id: QEMU netdev id that is connected
+# @addr: The destination address
+#
+# Since: 7.2
+#
+# Example:
+#
+# <- { "event": "NETDEV_STREAM_CONNECTED",
+#      "data": { "netdev-id": "netdev0",
+#                "addr": { "port": "47666", "ipv6": true,
+#                          "host": "::1", "type": "inet" } },
+#      "timestamp": { "seconds": 1666269863, "microseconds": 311222 } }
+#
+# or
+#
+# <- { "event": "NETDEV_STREAM_CONNECTED",
+#      "data": { "netdev-id": "netdev0",
+#                "addr": { "path": "/tmp/qemu0", "type": "unix" } },
+#      "timestamp": { "seconds": 1666269706, "microseconds": 413651 } }
+#
+##
+{ 'event': 'NETDEV_STREAM_CONNECTED',
+  'data': { 'netdev-id': 'str',
+            'addr': 'SocketAddress' } }
+
+##
+# @NETDEV_STREAM_DISCONNECTED:
+#
+# Emitted when the netdev stream backend is disconnected
+#
+# @netdev-id: QEMU netdev id that is disconnected
+#
+# Since: 7.2
+#
+# Example:
+#
+# <- { 'event': 'NETDEV_STREAM_DISCONNECTED',
+#      'data': {'netdev-id': 'netdev0'},
+#      'timestamp': {'seconds': 1663330937, 'microseconds': 526695} }
+#
+##
+{ 'event': 'NETDEV_STREAM_DISCONNECTED',
+  'data': { 'netdev-id': 'str' } }