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, 8 insertions, 0 deletions

diff --git a/migration/migration.h b/migration/migration.h
index d2269c826c..941c61e543 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -23,6 +23,7 @@
 #include "io/channel-buffer.h"
 #include "net/announce.h"
 #include "qom/object.h"
+#include "postcopy-ram.h"
 
 struct PostcopyBlocktimeContext;
 
@@ -112,6 +113,11 @@ struct MigrationIncomingState {
      * enabled.
      */
     unsigned int postcopy_channels;
+    /* QEMUFile for postcopy only; it'll be handled by a separate thread */
+    QEMUFile *postcopy_qemufile_dst;
+    /* Postcopy priority thread is used to receive postcopy requested pages */
+    QemuThread postcopy_prio_thread;
+    bool postcopy_prio_thread_created;
     /*
      * An array of temp host huge pages to be used, one for each postcopy
      * channel.
@@ -192,6 +198,8 @@ struct MigrationState {
     QEMUBH *cleanup_bh;
     /* Protected by qemu_file_lock */
     QEMUFile *to_dst_file;
+    /* Postcopy specific transfer channel */
+    QEMUFile *postcopy_qemufile_src;
     QIOChannelBuffer *bioc;
     /*
      * Protects to_dst_file/from_dst_file pointers.  We need to make sure we