Re: [Qemu-devel] [PATCH] migration: Correctly handle subsections with no 'needed' function

[Peter Maydell]

On 7 August 2018 at 16:05, Juan Quintela <address@hidden> wrote:
> Peter Maydell <address@hidden> 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.

In any case, for all the devices here the machine types are
not versioned.

thanks
-- PMM