Re: [PATCH v7 12/12] So we use multifd to transmit zero pages.

[Juan Quintela <quintela@redhat.com>]

Leonardo Brás <leobras@redhat.com> wrote:
> On Tue, 2022-08-02 at 08:39 +0200, Juan Quintela wrote:
>> Signed-off-by: Juan Quintela <quintela@redhat.com>

>> diff --git a/migration/multifd.c b/migration/multifd.c
>> index 89811619d8..54acdc004c 100644
>> --- a/migration/multifd.c
>> +++ b/migration/multifd.c
>> @@ -667,8 +667,8 @@ static void *multifd_send_thread(void *opaque)
>>  {
>>      MultiFDSendParams *p = opaque;
>>      Error *local_err = NULL;
>> -    /* qemu older than 7.0 don't understand zero page on multifd channel */
>> -    bool use_zero_page = migrate_use_multifd_zero_page();
>> +    /* older qemu don't understand zero page on multifd channel */
>> +    bool use_multifd_zero_page = !migrate_use_main_zero_page();
>
> I understand that "use_main_zero_page", which is introduced as a new capability,
> is in fact the old behavior, and the new feature is introduced when this
> capability is disabled.
>
> But it sure looks weird reading:
>  use_multifd_zero_page = !migrate_use_main_zero_page();
>
> This series is fresh in my mind, but it took a few seconds to see that this is
> actually not a typo. 

We can't have it both ways.

All other capabilities are false by default.  And libvirt assumes they
are false.  So, or we are willing to change the expectations, or we need
to do it this way.

In previous versions, I had the capability named the other way around,
and I changed it due to this.

Thanks, Juan.