main: send MSG_MIGRATE upon vm migration completion

Before sending the above msg, if there is a pending partial msg that
has been read from the agent, we send it to the client. The alternative
was to keep the msg as part of the migration data, and then
to send it to the destination server via the client and to wait there
for the msg chunk completion, before sending it to the client. Of
course, the latter is less efficient.

server/main_channel.c

@@ -1160,10 +1160,17 @@ uint64_t main_channel_client_get_bitrate_per_sec(MainChannelClient *mcc)
     return mcc->bitrate_per_sec;
 }
 
+static void main_channel_client_migrate(RedChannelClient *rcc)
+{
+    reds_on_main_channel_migrate(SPICE_CONTAINEROF(rcc, MainChannelClient, base));
+    red_channel_client_default_migrate(rcc);
+}
+
 MainChannel* main_channel_init(void)
 {
     RedChannel *channel;
     ChannelCbs channel_cbs = { NULL, };
+    ClientCbs client_cbs = {NULL, };
 
     channel_cbs.config_socket = main_channel_config_socket;
     channel_cbs.on_disconnect = main_channel_client_on_disconnect;
@@ -1187,6 +1194,9 @@ MainChannel* main_channel_init(void)
     spice_assert(channel);
     red_channel_set_cap(channel, SPICE_MAIN_CAP_SEMI_SEAMLESS_MIGRATE);
 
+    client_cbs.migrate = main_channel_client_migrate;
+    red_channel_register_client_cbs(channel, &client_cbs);
+
     return (MainChannel *)channel;
 }
 

server/red_channel.c

@@ -901,7 +901,7 @@ RedChannel *red_channel_create_parser(int size,
 
 void red_channel_register_client_cbs(RedChannel *channel, ClientCbs *client_cbs)
 {
-    spice_assert(client_cbs->connect);
+    spice_assert(client_cbs->connect || channel->type == SPICE_CHANNEL_MAIN);
     channel->client_cbs.connect = client_cbs->connect;
 
     if (client_cbs->disconnect) {

server/reds.c

@@ -1219,6 +1219,50 @@ void reds_on_main_mouse_mode_request(void *message, size_t size)
     }
 }
 
+/*
+ * Push partial agent data, even if not all the chunk was consumend,
+ * in order to avoid the roundtrip (src-server->client->dest-server)
+ */
+void reds_on_main_channel_migrate(MainChannelClient *mcc)
+{
+    VDIPortState *agent_state = &reds->agent_state;
+    uint32_t read_data_len;
+
+    spice_assert(reds->num_clients == 1);
+
+    if (agent_state->read_state != VDI_PORT_READ_STATE_READ_DATA) {
+        return;
+    }
+    spice_assert(agent_state->current_read_buf->data &&
+                 agent_state->recive_pos > agent_state->current_read_buf->data);
+    read_data_len = agent_state->recive_pos - agent_state->current_read_buf->data;
+
+    if (agent_state->read_filter.msg_data_to_read ||
+        read_data_len > sizeof(VDAgentMessage)) { /* msg header has been read */
+        VDIReadBuf *read_buf = agent_state->current_read_buf;
+
+        spice_debug("push partial read %u (msg first chunk? %d)", read_data_len,
+                    !agent_state->read_filter.msg_data_to_read);
+
+        read_buf->len = read_data_len;
+        if (vdi_port_read_buf_process(agent_state->vdi_chunk_header.port, read_buf)) {
+            main_channel_client_push_agent_data(mcc,
+                                                read_buf->data,
+                                                read_buf->len,
+                                                vdi_port_read_buf_release,
+                                                read_buf);
+        } else {
+            vdi_port_read_buf_unref(read_buf);
+        }
+
+        spice_assert(agent_state->recive_len);
+        agent_state->message_recive_len += agent_state->recive_len;
+        agent_state->read_state = VDI_PORT_READ_STATE_GET_BUFF;
+        agent_state->current_read_buf = NULL;
+        agent_state->recive_pos = NULL;
+    }
+}
+
 #define MAIN_CHANNEL_MIG_DATA_VERSION 1
 
 typedef struct WriteQueueInfo {

server/reds.h

@@ -159,6 +159,7 @@ void reds_on_main_mouse_mode_request(void *message, size_t size);
 int reds_on_migrate_dst_set_seamless(MainChannelClient *mcc, uint32_t src_version);
 void reds_on_client_semi_seamless_migrate_complete(RedClient *client);
 void reds_on_client_seamless_migrate_complete(RedClient *client);
+void reds_on_main_channel_migrate(MainChannelClient *mcc);
 void reds_on_char_device_state_destroy(SpiceCharDeviceState *dev);
 
 #endif