On 5/13/10, Jan Kiszka <jan.kis...@web.de> wrote: > From: Jan Kiszka <jan.kis...@siemens.com> > > Some legacy users (mostly PC devices) of vmstate_register manage > instance IDs on their own, and that unfortunately in a way that is > incompatible with automatically generated ones. This so far prevents > switching those users to vmstates that are registered by qdev. > > To establish a migration path, this patch introduces the concept of > alias IDs. They can be passed to an extended vmstate registration > service, and qdev provides a set service to be used during device init. > find_se will consider the alias in addition to the default ID. We can > then start generating the default ID automatically and writing it on > vmsave, thus converting that format without breaking support for upward > migration.
If this is only for compatibility, I think the name should show it, like vmstate_set_compat_instance_id(), or vmstate_set_legacy_instance_id(). That way, if there happens to be an incompatible version bump, the function name suggests that it can be removed. The function should also take a last_legacy_version_id parameter. Consider for example that a vmstate format with the legacy ID is currently used with version_id of 2. We also start using this compatibility system. A new, compatible version 3 arrives but we only want to support legacy ID for version 2, as indicated by last_legacy_version_id=2. Then with a new version, let's say 5, which is no longer compatible with 2 or 3, the legacy ID stuff can finally be thrown away. qdev.c should check if last_legacy_id >= minimum_version_id and complain otherwise.
