Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector

[Paolo Bonzini]

On 14/05/2015 11:36, Michael S. Tsirkin wrote:
> 
> There are three answers:
> 1.  Yes, it's sure to get detected because everything gets shifted
>     and then you get an unexpected string instead of next device name.
> 2.  If you want a more generic way to detect this, then please work
>     on changing format for devices generally so each device
>     section has a byte length attached to it. Then we know that
>     when we make changes, they are detected as device will end
>     earlier/later than expected.

No need for that.  Subsections were introduced exactly to allow a change
to be compatible in the common case and incompatible in the uncommon
case.  Check out "git log -- grep subsection -- savevm.c".

> 3.  You can have a different workaround: add property "skip config vec
>     on migration" and set it for old spapr machine types.
>     old types continue losing config vec; new ones work better.

Why in the world would you want that?

Paolo