migration: migrate-continue

A new qmp command allows the caller to continue from a given
paused state.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

migration/migration.c

@@ -1374,6 +1374,17 @@ void qmp_migrate_cancel(Error **errp)
     migrate_fd_cancel(migrate_get_current());
 }
 
+void qmp_migrate_continue(MigrationStatus state, Error **errp)
+{
+    MigrationState *s = migrate_get_current();
+    if (s->state != state) {
+        error_setg(errp,  "Migration not in expected state: %s",
+                   MigrationStatus_str(s->state));
+        return;
+    }
+    qemu_sem_post(&s->pause_sem);
+}
+
 void qmp_migrate_set_cache_size(int64_t value, Error **errp)
 {
     MigrationState *s = migrate_get_current();

qapi/migration.json

@@ -876,6 +876,23 @@
 ##
 { 'command': 'migrate_cancel' }
 
+##
+# @migrate-continue:
+#
+# Continue migration when it's in a paused state.
+#
+# @state: The state the migration is currently expected to be in
+#
+# Returns: nothing on success
+# Since: 2.11
+# Example:
+#
+# -> { "execute": "migrate-continue" , "arguments":
+#      { "state": "pre-switchover" } }
+# <- { "return": {} }
+##
+{ 'command': 'migrate-continue', 'data': {'state': 'MigrationStatus'} }
+
 ##
 # @migrate_set_downtime:
 #