Re: [PATCH v3 COLOPre 11/26] tools/libxl: introduce a new API libxl__domain_restore() to load qemu state

[Yang Hongyang <yanghy@cn.fujitsu.com>]

On 06/30/2015 12:38 AM, Ian Campbell wrote:
> On Thu, 2015-06-25 at 14:25 +0800, Yang Hongyang wrote:
>> Secondary vm is running in colo mode. So we will do
>> the following things again and again:
>> 1. suspend both primay vm and secondary vm
>> 2. sync the state
>> 3. resume both primary vm and secondary vm
>> We will send qemu's state each time in step2, and
>> slave's qemu should read it each time before resuming
>> secondary vm. Introduce a new API libxl__domain_restore()
>> to do it. This API should be called before resuming
>> secondary vm.
>
> I think before this patch the state was passed to qemu as a parameter
> when it was launched, is that correct? If so then that would be worth
> mentioning for completeness.

Inaccurate I think. What you said before is the normal migration, in that
case, yes, the state was passed to qemu as a parameter. With COLO, the
first step is live migration, so the state is still passed to qemu as a
parameter when the live migration ended. The new introduced API only used
when we need to restore the DM state after a checkpoint, at this point,
guest QEMU already started, we can not pass the state as a parameter like
we do on first boot, so we introduce this API to restore the state after
QEMU has started.

>
>> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
>> Cc: Anthony Perard <anthony.perard@citrix.com>
>> ---
>>   tools/libxl/libxl_dom_save.c | 49 ++++++++++++++++++++++++++++++++++++++++++++
>>   tools/libxl/libxl_internal.h |  3 +++
>>   tools/libxl/libxl_qmp.c      | 10 +++++++++
>>   3 files changed, 62 insertions(+)
>>
>> diff --git a/tools/libxl/libxl_dom_save.c b/tools/libxl/libxl_dom_save.c
>> index 8fe1625..0ad2894 100644
>> --- a/tools/libxl/libxl_dom_save.c
>> +++ b/tools/libxl/libxl_dom_save.c
>> @@ -639,6 +639,55 @@ int libxl__toolstack_restore(uint32_t domid, const uint8_t *buf,
>>       }
>>       return 0;
>>   }
>> +
>> +static int libxl__domain_restore_device_model(libxl__gc *gc, uint32_t domid);
>> +
>> +int libxl__domain_restore(libxl__gc *gc, uint32_t domid)
>
> We don't have any libxl__domain_save counterpart, but we do have
> libxl__domain_save_device_model, so I wonder if the upcoming callers
> ought to just call that direct? Especially given that this function
> isn't any kind of generic domain restore, but has rather specific
> functionality (in particular it fails for PV guests).

Maybe we just introduce libxl__domain_restore_device_model() and call
this when needed, discard the new libxl__domain_restore() API, what do
you think?

>
>
> .
>

-- 
Thanks,
Yang.