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, 1 insertions, 0 deletions

diff --git a/migration/socket.h b/migration/socket.h
index 891dbccceb..dc54df4e6c 100644
--- a/migration/socket.h
+++ b/migration/socket.h
@@ -21,6 +21,7 @@
 #include "io/task.h"
 
 void socket_send_channel_create(QIOTaskFunc f, void *data);
+QIOChannel *socket_send_channel_create_sync(Error **errp);
 int socket_send_channel_destroy(QIOChannel *send);
 
 void socket_start_incoming_migration(const char *str, Error **errp);