Re: [Qemu-devel] [PATCH v2 5/6] e1000: Choose which set of props to migrate

[Jason Wang <jasowang@redhat.com>]

On 2018年03月29日 16:08, Dr. David Alan Gilbert wrote:
> * Jason Wang (jasowang@redhat.com) wrote:
>>
>> On 2018年03月29日 00:36, Dr. David Alan Gilbert (git) wrote:
>>> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>>>
>>> When we're using the subsection we migrate both
>>> the 'props' and 'tso_props' data; when we're not using
>>> the subsection (to migrate to 2.11 or old machine types) we've
>>> got to choose what to migrate in the main structure.
>>>
>>> If we're using the subsection migrate 'props' in the main structure.
>>> If we're not using the subsection then migrate the last one
>>> that changed, which gives behaviour similar to the old behaviour.
>>>
>>>
>> But only after migration. Why not simply switch back to the old behavior if
>> migrate_tso_props if false?
> Because:
>    1) We know it's a broken behaviour so it's better not to unfix it
>    2) The fix doesn't change guest visible behaviour other than actually
>       sending the right packets; so there's no reason to make the fix
>       itself dependent on the machine type.
>    3) Gating the fix itself on the flag is actually more complex and
>       would need checking the flag in lots of places that are already
>       pretty complex, rather than what this does which is just check it
>       in one place at migration.

It looks to me it was just something like:

     struct e1000x_txd_props *props = tp->cptse && chkflag(TSO) ? 
&tp->tso_props : &tp->props;

Btw, did this patch work when:

migrate A to B
migrate B to C

But there's no tx during B?

Thanks

>
> Dave
>> Thanks
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>