Peter Maydell <peter.mayd...@linaro.org> wrote: D> On 7 August 2018 at 16:05, Juan Quintela <quint...@redhat.com> wrote: >> Peter Maydell <peter.mayd...@linaro.org> wrote: >>> So it's better to use a needed-always subsection, which will give >>> the desired behaviour: >>> * new QEMU -> new QEMU: state is always migrated >>> * old QEMU -> new QEMU: migration doesn't fail, and guest >>> will work assuming it didn't care about this corner of the >>> device's functionality (the device will end up with state >>> as it was at reset, or possibly special-cased via >>> pre_load/post_load hooks for the "section not present" case) >> >> we break by definiton new QEMU -M <old machine type> into old QEMU. > > Is that supposed to work? I always thought that we never > supported migration back to an older QEMU version like that.
It is a "best effort" case. As David told, downstream we try very hard. For upstream we do when I found that, but not anywhere else. > In any case, for all the devices here the machine types are > not versioned. This is part of the problem. For some architectures, we don't even care about migraiton. For others, we care about migration but not cross-version. And yet in others we care very much (downstream specially). And it is not clear what devices support each of them. Later, Juan.
