On 21 December 2015 at 22:25, Andrew Baumann <andrew.baum...@microsoft.com> wrote:
>> If you change the VMSTATE layout, you need to bump the version. As >> this is very common code, it may have stricter version bump >> requirements. Last I knew however, there was a way to add new fields >> at the end of VMSD without breaking backwards compatibility. Peter or >> Juan may know more. > > I'll admit that I didn't think about these issues when adding the > fields, but after a (quick) look at vmstate_save_state() and > vmstate_load_state(), they seem to be using named fields in a json > format, so I don't think the order of fields should matter if we are > adding new ones. The on-the-wire format is not json, and order is important; field names are not sent. If we care about migration compatibility I think the recommendation is to use subsections, rather than marking fields as only existing in particular versions. (see docs/migration.txt for a discussion of subsections). thanks -- PMM
