migrate_start_postcopy: Command to trigger transition to postcopy

Once postcopy is enabled (with migrate_set_capability), the migration
will still start on precopy mode.  To cause a transition into postcopy
the:

  migrate_start_postcopy

command must be issued.  Postcopy will start sometime after this
(when it's next checked in the migration loop).

Issuing the command before migration has started will error,
and issuing after it has finished is ignored.

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

1 files changed, 19 insertions, 0 deletions

diff --git a/qmp-commands.hx b/qmp-commands.hx
index d7cf0ff..7f85d40 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -718,6 +718,25 @@ Example:
 
 EQMP
     {
+        .name       = "migrate-start-postcopy",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_migrate_start_postcopy,
+    },
+
+SQMP
+migrate-start-postcopy
+----------------------
+
+Switch an in-progress migration to postcopy mode. Ignored after the end of
+migration (or once already in postcopy).
+
+Example:
+-> { "execute": "migrate-start-postcopy" }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "query-migrate-cache-size",
         .args_type  = "",
         .mhandler.cmd_new = qmp_marshal_query_migrate_cache_size,