the primary API realization.

Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <1539795177-21038-3-git-send-email-peng.hao2@zte.com.cn>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>