Am 13.05.2015 um 18:14 schrieb Michael S. Tsirkin: >> - AFAICS, there's no easy way to add transport-specific subsections - >> and simply adding config_vector in ccw would break compatibility > > subsections break compatibility too. The only way around that is to set > a flag to skip migrating config_vector for old machine types.
My main concern is about undetected compatibility issues. A subsection will tell the user that something went wrong. What happens if we just add a new qemu_put_byte in the stream. Will the savevm core always detect that we have too many or not enough bytes? If yes, adding new stuff in the stream will always be detected in some way as error we can go with just adding qemu_put_be16/qemu_get_be16 in virtio_ccw_save_config/virtio_ccw_load_config. Old/new QEMUs will then not be compatible - but thats probably ok as long as it errors out. My understanding was that we do not have a guarentee that this will be detected all the time and having random junk in some variables is a debugging nightmare. Is that correct? Christian
