(ITS#5365) Library symbol versioning or other help for library transitions

[rra@stanford.edu]

Full_Name: Russ Allbery
Version: 2.4.7
OS: Debian GNU/Linux
URL: 
Submission from: (NULL) (171.66.157.14)


One of the challenges of handling core system libraries like OpenLDAP in the
context of a packaged distribution is handling library transitions when the
SONAME of the library changes (such as between 2.3 and 2.4, and presumably
between 2.4 and 2.5).  It's rarely possible to rebuild every package at the same
time against the newer libraries (particularly since there are dependency chains
that often require one package go first before another can be rebuilt), let
alone all of the user software that's outside the space managed by the
distribution.  Because of that, both the old and new library usually have to
co-exist for at least a brief period on many systems, with some binaries linked
against the old version and some against the new version, until the upgrade is
complete.

This is, fundamentally, the problem of the distribution and not the problem of
the OpenLDAP team.  However, one thing that, from a distributor perspective,
helps considerably with transitions like this is if the upstream library
distributor uses symbol versioning on those platforms that support it (primarily
Linux and Solaris, and possibly -- I have no personal experience -- the *BSDs). 
If symbol versioning is used for the libraries, the 2.3 and 2.4 libraries can be
loaded into the same namespace and won't conflict with each other, since the
programs and other libraries will bind to the version against which they were
compiled.

So, basically, this is a feature request: would it be possible to add symbol
versioning to the libldap and libber libraries?  Very simple symbol versioning
(just assigning one version to all public symbols) would be sufficient to make
these sorts of transitions much easier.  I'm happy to help provide information
and Makefile glue to do this if it's desirable; I've done it in a portable way
with several other libraries in packages I maintain.

Please feel free to tell me I should move this to a post to openldap-technical
or somewhere else; I know it's sort of borderline between an ITS and a library
usage discussion.