Re: Shared library versioning

[Bob Friesenhahn]

On Tue, 14 Jun 2011, Lasse Collin wrote:
> If I add a new public function to a library and don't modify anything
> else, I should do ++current, ++age, revision=0, right? For example, if
> the previous version of the library uses current:revision:age = 1:3:0,
> adding a new function would make it 2:0:1. On GNU/Linux, this becomes
>
>    libfoo.so.1.0.3 -> libfoo.so.1.1.0
>
> which is fine. On OpenBSD, GNU Libtool does
>
>    libfoo.so.1.3 -> libfoo.so.2.0
>
> while the correct thing, according to the OpenBSD docs, would be this:
>
>    libfoo.so.1.0 -> libfoo.so.1.1
>
> That is, revision isn't visible anywhere. The filename doesn't change if
> only bug fixes have been made and the library ABI hasn't been touched
> (nothing added, removed, or changed). Please read the section
> "Understanding shared libraries number rules" (it's short):
>
>    http://www.openbsd.org/faq/ports/specialtopics.html

If this web page text is correct, then I agree that libtool is doing 
the wrong thing for OpenBSD.  But of course we should search for any 
additional information and consult with relevant OpenBSD maintainers 
before making any such change since FAQ text could easily be wrong.

> > The applications are really what care about the library versioning.
> > The OS is just there to help with the selection process.
>
> Packagers care about library versions too. Incrementing the major
> version means that packagers need to recompile everything that depend on
> the library. It is annoying if the major version is incremented without
> a reason.

The major version ("current") was certainly incremented for a reason. 
It is true that if there is a sea of existing libraries which depend 
on the older version of the library then there may be problems if you 
attempt to relink with a newer version of the library since the linker 
may bring in several versions of the same library.  These issues are 
highly OS dependent.

Bob
--
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/