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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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.

Wei.

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

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