migration: Postcopy preemption preparation on channel creation

Create a new socket for postcopy to be prepared to send postcopy requested
pages via this specific channel, so as to not get blocked by precopy pages.

A new thread is also created on dest qemu to receive data from this new channel
based on the ram_load_postcopy() routine.

The ram_load_postcopy(POSTCOPY) branch and the thread has not started to
function, and that'll be done in follow up patches.

Cleanup the new sockets on both src/dst QEMUs, meanwhile look after the new
thread too to make sure it'll be recycled properly.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20220707185502.27149-1-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  dgilbert: With Peter's fix to quieten compiler warning on
       start_migration

1 files changed, 21 insertions, 1 deletions

diff --git a/migration/socket.c b/migration/socket.c
index 4fd5e85f50..e6fdf3c5e1 100644
--- a/migration/socket.c
+++ b/migration/socket.c
@@ -26,7 +26,7 @@
 #include "io/channel-socket.h"
 #include "io/net-listener.h"
 #include "trace.h"
-
+#include "postcopy-ram.h"
 
 struct SocketOutgoingArgs {
     SocketAddress *saddr;
@@ -39,6 +39,24 @@ void socket_send_channel_create(QIOTaskFunc f, void *data)
                                      f, data, NULL, NULL);
 }
 
+QIOChannel *socket_send_channel_create_sync(Error **errp)
+{
+    QIOChannelSocket *sioc = qio_channel_socket_new();
+
+    if (!outgoing_args.saddr) {
+        object_unref(OBJECT(sioc));
+        error_setg(errp, "Initial sock address not set!");
+        return NULL;
+    }
+
+    if (qio_channel_socket_connect_sync(sioc, outgoing_args.saddr, errp) < 0) {
+        object_unref(OBJECT(sioc));
+        return NULL;
+    }
+
+    return QIO_CHANNEL(sioc);
+}
+
 int socket_send_channel_destroy(QIOChannel *send)
 {
     /* Remove channel */
@@ -166,6 +184,8 @@ socket_start_incoming_migration_internal(SocketAddress *saddr,
 
     if (migrate_use_multifd()) {
         num = migrate_multifd_channels();
+    } else if (migrate_postcopy_preempt()) {
+        num = RAM_CHANNEL_MAX;
     }
 
     if (qio_net_listener_open_sync(listener, saddr, num, errp) < 0) {