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

[Yang Hongyang <yanghy@xxxxxxxxxxxxxx>]

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.

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