Return path: Send responses from destination to source

Add migrate_send_rp_message to send a message from destination to source along the return path.
  (It uses a mutex to let it be called from multiple threads)
Add migrate_send_rp_shut to send a 'shut' message to indicate
  the destination is finished with the RP.
Add migrate_send_rp_ack to send a 'PONG' message in response to a PING
  Use it in the MSG_RP_PING handler

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 98a6d079fd..3ce3fda6b7 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -43,12 +43,22 @@ struct MigrationParams {
     bool shared;
 };
 
+/* Messages sent on the return path from destination to source */
+enum mig_rp_message_type {
+    MIG_RP_MSG_INVALID = 0,  /* Must be 0 */
+    MIG_RP_MSG_SHUT,         /* sibling will not send any more RP messages */
+    MIG_RP_MSG_PONG,         /* Response to a PING; data (seq: be32 ) */
+
+    MIG_RP_MSG_MAX
+};
+
 typedef QLIST_HEAD(, LoadStateEntry) LoadStateEntry_Head;
 /* State for the incoming migration */
 struct MigrationIncomingState {
     QEMUFile *from_src_file;
 
     QEMUFile *to_src_file;
+    QemuMutex rp_mutex;    /* We send replies from multiple threads */
 
     /* See savevm.c */
     LoadStateEntry_Head loadvm_handlers;
@@ -181,6 +191,15 @@ int migrate_compress_threads(void);
 int migrate_decompress_threads(void);
 bool migrate_use_events(void);
 
+/* Sending on the return path - generic and then for each message type */
+void migrate_send_rp_message(MigrationIncomingState *mis,
+                             enum mig_rp_message_type message_type,
+                             uint16_t len, void *data);
+void migrate_send_rp_shut(MigrationIncomingState *mis,
+                          uint32_t value);
+void migrate_send_rp_pong(MigrationIncomingState *mis,
+                          uint32_t value);
+
 void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_after_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_load_hook(QEMUFile *f, uint64_t flags, void *data);