On Fri, Nov 02, 2018 at 09:44:54AM -0700, Jim Mattson via Qemu-devel wrote: > On Fri, Nov 2, 2018 at 5:59 AM, Liran Alon <liran.alon@xxxxxxxxxx> wrote: > > > > >>> Therefore, I don't think that we want this versioning to be based on KVM_CAP at all. > >>> It seems that we would want the process to behave as follows: > >>> 1) Mgmt-layer at dest queries dest host max supported nested_state size. > >>> (Which should be returned from kvm_check_extension(KVM_CAP_NESTED_STATE)) > >>> 2) Mgmt-layer at source initiate migration to dest with requesting QEMU to send nested_state > >>> matching dest max supported nested_state size. > >>> When saving nested state using KVM_GET_NESTED_STATE IOCTL, QEMU will specify in nested_state->size > >>> the *requested* size to be saved and KVM should be able to save only the information which matches > >>> the version that worked with that size. > >>> 3) After some sanity checks on received migration stream, dest host use KVM_SET_NESTED_STATE IOCTL. > >>> This IOCTL should deduce which information it should deploy based on given nested_state->size. > > I have to object to any proposal which requires the management later > to communicate with the source and the destination to determine what > should be done. Can you elaborate on why you object ? There are a bunch of features in QEMU's migration code which require the mgmt layer to look at source + dest to determine what should be done. Admittedly the cases we have had so far are generic migration features (compression, multifd, postcopy, TLS, etc), while this is a host kernel feature. I don't think it is that far outside the normal practice wrt migration feature usage decision making though. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
