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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Jan 27, 2016 at 03:15:47PM +0000, Andrew Cooper wrote:
> 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@cn.fujitsu.com>
> >>>>> Signed-off-by: Yang Hongyang <hongyang.yang@easystack.cn>
> >>>>> ---
> >>>>>  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@citrix.com>>
> >>>>> -% 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.

You are still not answering my question.

Is it a hard error if the mandatory record is zero length?

> 
> ~Andrew