Re: [Xen-devel] [PATCH v9 02/25] docs/libxl: Introduce COLO_CONTEXT to support migration v2 colo streams

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 27/01/16 15:11, Konrad Rzeszutek Wilk wrote:
> On Wed, Jan 27, 2016 at 11:00:24AM +0000, Andrew Cooper wrote:
>> On 27/01/16 06:47, Wen Congyang wrote:
>>> On 01/27/2016 04:40 AM, Konrad Rzeszutek Wilk wrote:
>>>> On Wed, Dec 30, 2015 at 10:37:32AM +0800, Wen Congyang wrote:
>>>>> It is the negotiation record for COLO.
>>>>> Primary->Secondary:
>>>>> control_id      0x00000000: Secondary VM is out of sync, start a new 
>>>>> checkpoint
>>>>> Secondary->Primary:
>>>>>                 0x00000001: Secondary VM is suspended
>>>>>                 0x00000002: Secondary VM is ready
>>>>>                 0x00000003: Secondary VM is resumed
>>>>>
>>>>> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
>>>>> Signed-off-by: Yang Hongyang <hongyang.yang@xxxxxxxxxxxx>
>>>>> ---
>>>>>  docs/specs/libxl-migration-stream.pandoc | 25 +++++++++++++++++++++++--
>>>>>  tools/libxl/libxl_sr_stream_format.h     | 11 +++++++++++
>>>>>  tools/python/xen/migration/libxl.py      |  9 +++++++++
>>>>>  3 files changed, 43 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/docs/specs/libxl-migration-stream.pandoc 
>>>>> b/docs/specs/libxl-migration-stream.pandoc
>>>>> index 2c97d86..5166d66 100644
>>>>> --- a/docs/specs/libxl-migration-stream.pandoc
>>>>> +++ b/docs/specs/libxl-migration-stream.pandoc
>>>>> @@ -1,6 +1,6 @@
>>>>>  % LibXenLight Domain Image Format
>>>>>  % Andrew Cooper <<andrew.cooper3@xxxxxxxxxx>>
>>>>> -% Revision 1
>>>>> +% Revision 2
>>>>>  
>>>>>  Introduction
>>>>>  ============
>>>>> @@ -119,7 +119,9 @@ type         0x00000000: END
>>>>>  
>>>>>               0x00000004: CHECKPOINT_END
>>>>>  
>>>>> -             0x00000005 - 0x7FFFFFFF: Reserved for future _mandatory_
>>>>> +             0x00000005: CHECKPOINT_STATE
>>>>> +
>>>>> +             0x00000006 - 0x7FFFFFFF: Reserved for future _mandatory_
>>>> This is in the 'mandatory' records. Should it be part of optional records?
>>>>
>>>> Would this checkpoint state always present on non-COLO guest migration?
>>> No. Will be fixed in the next version
>> It is correct that CHECKPOINT_STATE is a mandatory record.
>>
>> Optional records which are free for the receiving end to ignore if they
>> are not understood.
> What you are saying is that the receving end has to expect this 
> (CHECKPOINT_STATE)
> even there is nothing in them - as the size of them is zero (becuase there are
> no  dirty PFNs to send).

The sole difference between a mandatory record an an option record is
the receivers behaviour.

Mandatory records may not be ignored, and constitutes a hard error. 
Optional records may be ignored, without error, if they are not understood.

~Andrew

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