On 22 March 2011 19:53, Juan Quintela <quint...@redhat.com> wrote:
> Peter Maydell <peter.mayd...@linaro.org> wrote:
>> Migration from the old version to the new version can be supported
>> if it is OK for the new fields to remain in their default state
>> [XXX is this right? are they zeroed, or do they get the value
>> the device's reset function sets them to, or something else?]
>
> You can initialize in your init function at the value that you want, or
> use foo_post_load() function (that receives the version as a parameter)
> to assign to any correct values that you need.
To check I understand this, this means an incoming migration is
always done to a fresh, never-been-used-before device that has had
its init called but not its reset?
>> when the state of an old-version snapshot is loaded. To implement
>> this you need to use the VMSTATE_*_V macros which let you specify
>> the version in which a field was introduced, for instance:
>>
>> VMSTATE_UINT32_V(sys_cfgdata, arm_sysctl_state, 2)
>>
>> for a field introduced in version 2. You should also increment
>> the version_id, but leave the minimum_version_id unchanged.
>> Newly added VMSTATE_*_V fields should go at the end of the
>> VMState description.
>
> Just to make things more complicated, this has been "deprecated" O:-)
It has? Your examples below still use it...
> - We know that old device was wrong, and that there is no way we can
> load (reliabely) from version 0. Then we just increase the version:
If you're increasing the version can you also clean up by
converting any old VMSTATE_*_V() into plain VMSTATE_*() at this
point, since we can't migrate from those old versions any more?
> - We know that we can load from v1. But that we want to always sent
> bar2 for migration, then we just increase versions to:
>
>
> const VMStateDescription vmstate_foo = {
> .name = "foo",
> .version_id = 2,
> .minimum_version_id = 1,
> .minimum_version_id_old = 1,
> .fields = (VMStateField []) {
> VMSTATE_INT32(bar, FOOState),
> VMSTATE_INT32_V(bar2, FOOState, 1),
> VMSTATE_END_OF_LIST()
> }
> };
>
> And we are done. We are able to receive state 0 and 1, and we would
> always sent version 1.
Your numbers in the struct and the text don't seem to match?
My guess is you meant to write version_id = 1, minimum_version* = 0 ?
> Have I manage to explain myself a little bit?
Yes, thanks, that's very helpful.
-- PMM
