Re: [PATCH v2 COLOPre 11/13] tools/libxl: rename remus device to checkpoint device

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

On 06/25/2015 05:09 PM, Wei Liu wrote:
> On Thu, Jun 25, 2015 at 01:00:14PM +0800, Yang Hongyang wrote:
>>
>>
>> On 06/16/2015 06:53 PM, Ian Campbell wrote:
>>> On Mon, 2015-06-15 at 17:24 +0100, Wei Liu wrote:
>>>> On Mon, Jun 15, 2015 at 09:45:54AM +0800, Yang Hongyang wrote:
>>>>>
>>>>>
>>>>> On 06/12/2015 10:57 PM, Ian Jackson wrote:
>>>>>> Wei Liu writes ("Re: [Xen-devel] [PATCH v2 COLOPre 11/13] tools/libxl: rename remus device to checkpoint device"):
>>>>>>> On Fri, Jun 12, 2015 at 02:30:46PM +0100, Wei Liu wrote:
>>>>>>>> On Mon, Jun 08, 2015 at 11:43:15AM +0800, Yang Hongyang wrote:
>>>>>>>>> -    (-18, "REMUS_DEVOPS_DOES_NOT_MATCH"),
>>>>>>>>> -    (-19, "REMUS_DEVICE_NOT_SUPPORTED"),
>>>>>>>>> +    (-18, "CHECKPOINT_DEVOPS_DOES_NOT_MATCH"),
>>>>>>>>> +    (-19, "CHECKPOINT_DEVICE_NOT_SUPPORTED"),
>>>>>>>>
>>>>>>>> You should add two new error numbers.
>>>>>>>>
>>>>>>>
>>>>>>> And in that case you might also need to go through all places to make
>>>>>>> sure the correct error numbers are return. I.e. old remus code path
>>>>>>> still returns REMUS error code and new CHECKPOINT code path returns new
>>>>>>> error code.
>>>>>>>
>>>>>>> I merely speak from API backward compatibility point of view. If you
>>>>>>> think what I suggest doesn't make sense, please let me know.
>>>>>>
>>>>>> To me this line of reasons prompts me to ask: what would be wrong with
>>>>>> leaving the word REMUS in the error names, and simply updating the
>>>>>> descriptions ?
>>>>>>
>>>>>> After all AFIACT the circumstances are very similar.  I don't think it
>>>>>> makes sense to require libxl to do something like
>>>>>>     rc = were_we_doing_colo_not_remus ? CHECKPOINT_BLAH : REMUS_BLAH;
>>>>>>
>>>>>> Please to contradict me if I have misunderstood...
>>>>>
>>>>> COLO and REMUS both are checkpoint device. We use checkpoint device layer
>>>>> as a more abstract layer for both COLO and REMUS, come to the error code,
>>>>> these can be used by both COLO and REMUS. So we don't distinguish if we
>>>>> are doing COLO or REMUS, uses are aware of what they're executing(colo
>>>>> or remus).
>>>>>
>>>>
>>>> Right. So continue using REMUS_ error code is fine.
>>>
>>> Seems like it would also be OK to switch the name and then in libxl,h
>>>
>>> #ifdef LIB_API_VERSION < 0xWHENEVER
>>> #define REMUS_BLAH CHECKPOINT_BLAH
>>> #define ...
>>> #endif
>>>
>>> _If_ we think the new names make more sense going fwd...
>>
>> Well, I think the new names are better, I also think it is safe to just rename
>> them, I don't find any other users using these error codes except Remus/COLO,
>> it is only used by Remus/COLO internally.
>>
>
> The main point is, this is external visible interface. Some user might
> have also developed their solution based on remus. In their code they
> check for REMUS_$FOO error code.
>
> I agree renaming to CHECKPOINT even for the sake of matching API names
> is good. I think Ian's suggestion should be the simplest way of moving
> forward.

Ok, will add an extra patch to deal with this back compatibility issue
in the next version.

>
> Wei.
>
>>>
>>>
>>> .
>>>
>>
>> --
>> Thanks,
>> Yang.
> .
>

-- 
Thanks,
Yang.