[Pkg-vsquare-devel] Bug#610933: libvdeplug3 declares a conflict with libvdeplug2

[Jonathan Nieder]

Ludovico Gardenghi wrote:

> (In any case, I still can't figure out what should be the *proper* way
> for a program for dlopening a .so while providing the version number...
> should it loop over all the (infinite :-)) possible SONAMEs who offer
> compatibility for the needed interface version?

Ah!  Well, it's true that SONAMEs are not a perfect description of
whether the relevant part of the interface changed or not.

When the SONAME is bumped, programs that linked directly to the
library still are linked to the old version.  This has a few
implications:

 1. If you want to dlopen a shared library, in general one practical
    way to do so is to call "readlink" on the .so symlink at build
    time and then strip off the minor version (for example in your
    configure script) and bake in the target.  This way, if later
    versions of the shared library change or remove the interfaces you
    are using, your program will still work.

    Is there any particular reason for libvdeplug_dyn.h to use the
    unversioned name instead of "libvdeplug.so.3"?

 2. If the SONAME of a shared library is changing very often, that
    means old programs linking to the old version are going to
    cause a lot of crufty old versions to be kept around on some
    machines.  If the SONAME is bumping often enough for this to
    be a problem, it can be useful to find ways to make the interface
    a little more stable :) --- for example, by using opaque types,
    and by using symbol versioning to version backward-compatible
    ABI extensions.