Re: [Qemu-devel] [PATCHv2] rtl8139: save/load RxMulOk counter (again)

[Paolo Bonzini]

On 21/06/2016 03:44, Jason Wang wrote:
> 
> 
> On 2016年06月21日 01:53, David Vrabel wrote:
>> Commit 9d29cdeaaca3a0383af764000b71492c4fc67c6e (rtl8139: port
>> TallyCounters to vmstate) introduced in incompatibility in the v4
>> format as it omitted the RxOkMul counter.
>>
>> There are presumably no users that were impacted by the v4 to v4'
>> breakage, so increase the save version to 5 and re-add the field,
>> keeping backward compatibility with v4'.
>>
>> We can't have a field conditional on the section version in
>> vmstate_tally_counters since this version checked would not be the
>> section version (but the version defined in this structure).  So, move
>> all the fields into the main state structure.
>>
>> Signed-off-by: David Vrabel <address@hidden>
> 
> Migration to old version is important for the user and this patch seems
> to break this. How about something like:
> 
> - introduce a subsection for RXOKMul
> - only migrate it for new version (e.g >= 2.7)

Introducing a subsection is not really necessary if the value is going
to be migrated always, and upstream generally does not have "migrate it
only in some version" checks.  This is left for downstreams to implement
if they care.  We just don't have the manpower to ensure that migration
to older versions works between all releases of QEMU.

Paolo