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

[David Vrabel <david.vrabel@citrix.com>]

On 21/06/16 08:35, Paolo Bonzini wrote:
> 
> 
> 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 <david.vrabel@citrix.com>
>>
>> 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)

I don't see how this can work with snapshots where the QEMU version that
is going to restore the snapshot is not known in advance.

> 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.

So is this patch acceptable as is?

David