[dm-devel] [PATCH 10/11] libmpathpersist: add linker version script

[Benjamin Marzinski]

On Fri, Sep 25, 2020 at 09:52:51PM +0200, Martin Wilck wrote:
> On Thu, 2020-09-24 at 23:00 -0500, Benjamin Marzinski wrote:
> > On Thu, Sep 24, 2020 at 03:36:43PM +0200, mwilck at suse.com wrote:
> > > 
> > > --- /dev/null
> > > +++ b/libmpathpersist/libmpathpersist.version
> > > @@ -0,0 +1,20 @@
> > > +LIBMPATHPERSIST_0.8.4.0 {
> > 
> > I have a question about this version. Do you plan on bumping this
> > each
> > time a new release is tagged? It seems like we only ever want to
> > change
> > the version if we actually change the ABI. Or is 0.8.4 just because
> > that's the relesae where we started this?
> 
> That was the idea, yes. And the last digit is because we'll have to
> bump it between releases from Christophe. It makes sense for
> libmultipath's rapidly changing ABI; much less so for libmpathcmd and
> libmpathpersist, which are meant to be stable. I am open for discussing
> these numbers; if you prefer, we might as well use LIBMPATHPERSIST_1.0.
> 
> I admit I haven't thought about what would happen once Christophe makes
> a new release. Probably, nothing - afaics it's impossible to add a new
> version without any new symbols, and *renaming* an existing version is
> bad; it would introduce artificial incompatibility. 
> 
> So libmultipath from multipath-tools 0.8.5 would still have a 0.8.4.x
> ABI; only the first change after 0.8.5 would get a 0.8.5.1 number. Hm.
> 
> Again, I'm open for discussion here. We might as well choose to not tie
> the ABI version to the libmultipath version at all, and simply start at
> 0.1 or whatevever for libmultipath. After all, looking up the ABI
> version in the commit history will be simple enough.

Since the ABI version isn't always going to match the release version, I
think it makes more sense to decouple them, so it's not sometimes
matching and sometimes not. We could go with a MAJOR.MINOR versioning
scheme, where we bump MINOR whenever we change the interface in a
backwards compatible way (like by adding a new symbol), and bump the
MAJOR and reset the MINOR whenever we change the interface in a
non-backwards compatible way (like by changing the parameters an
interface function takes, or removing a symbol). Although I'm not sure
we need to be so careful for libmultipath, since that library isn't for
external consumption.

-Ben
 
> Martin
>