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, 3 insertions, 1 deletions

diff --git a/migration/ram.h b/migration/ram.h
index ded0a3a086..5d90945a6e 100644
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -61,7 +61,7 @@ void ram_postcopy_send_discard_bitmap(MigrationState *ms);
 /* For incoming postcopy discard */
 int ram_discard_range(const char *block_name, uint64_t start, size_t length);
 int ram_postcopy_incoming_init(MigrationIncomingState *mis);
-int ram_load_postcopy(QEMUFile *f);
+int ram_load_postcopy(QEMUFile *f, int channel);
 
 void ram_handle_compressed(void *host, uint8_t ch, uint64_t size);
 
@@ -73,6 +73,8 @@ int64_t ramblock_recv_bitmap_send(QEMUFile *file,
                                   const char *block_name);
 int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *rb);
 bool ramblock_page_is_discarded(RAMBlock *rb, ram_addr_t start);
+void postcopy_preempt_shutdown_file(MigrationState *s);
+void *postcopy_preempt_thread(void *opaque);
 
 /* ram cache */
 int colo_init_ram_cache(void);