Paolo Bonzini <pbonzini@xxxxxxxxxx> writes: > Il 02/07/2012 02:29, Rusty Russell ha scritto: >> VIRTIO_BALLOON_F_MUST_TELL_HOST >> implies you should tell the host (eventually). I don't know if any >> implementations actually care though. > > This is indeed broken, because it is a "negative" feature: it tells you > that "implicit deflate" is _not_ supported. > > Right now, QEMU refuses migration if the target does not support all the > features that were negotiated. But then: > > - a migration from non-MUST_TELL_HOST to MUST_TELL_HOST will succeed, > which is wrong; > > - a migration from MUST_TELL_HOST to non-MUST_TELL_HOST will fail, which > is useless. > >> We could add a VIRTIO_BALLOON_F_NEVER_TELL_DEFLATE which would mean the >> deflate vq need not be used at all. > > That would work. At the same time we could deprecate MUST_TELL_HOST. > Certainly the guest implementations don't care, or we would have > experienced problems such as the one above. The QEMU implementation > also does not care but, for example, a Xen implementation would care. OK; I'm not sure we need to deprecate MUST_TELL_HOST, though since it's never actually been used there's a good argument. VIRTIO_BALLOON_F_SILENT_DEFLATE (or whatever it's called) would obviously mean you couldn't ack VIRTIO_BALLOON_F_MUST_TELL_HOST. Patches welcome! Cheers, Rusty. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
