[Fedora-packaging] Request for Guideline Clarification

[Michael Schwendt]

On Tue, 05 Jan 2010 22:24:22 -0500, Rich wrote:

> I went ahead and created a set of draft guidelines for discussion, 
> located at https://fedoraproject.org/wiki/PackagingDrafts/SharedLibraries
> 
> I tried to go by common practices, what the FHS states, etc.  Let me 
> know if I've missed the mark on anything or left something out.

Much too vague/ambiguous, especially for newbie packagers, who feel
clobbered by the current guidelines already. It is increasingly difficult
to create guidelines that simply say "do this" or "don't do that" without
giving a clear but long rationale that covers corner-cases even.

| If a library is providing resources that other packages may need at
| compile or runtime,

The difference between compile- and runtime is important enough not
to cover both in the same sentence. Also, what "resources" do you
refer to here?

| it should be installed directly to the default
| library search path.

Why? And why "the default"?

| Wherever possible, these libraries should be created with versioning in
| the filename,

Vague.

| and provide a set of unversioned symlinks in a -devel file.

This adds confusion. It is perfectly valid for a library to be called
libfoo-0.10.so.0 with a libfoo-0.10.so symlink.

| In the case that a package only contains unversioned libraries, they
| may be included in the non-devel base packages.

Insufficient for a general guideline. See further below in this mail, too.

| If libraries are installed into a subdirectory and do need to be on the
| system library search path, an entry in /etc/ld.so.conf.d/ may be created
| to add a subdirectory to the ld search path

If at all, there could be a future section on documenting ld.so.conf usage
a bit more. Adding library search paths that way effectively makes the
libs available to the run-time linker prior to searching in the trusted
default paths.

| Libraries in %{_libdir} subdirectores do not need versioning in their
| filenames.

But of course they do, if you add them via ld.so.conf.d entries.
"ldconfig -vp|less" The filename is not so important. A library's SONAME is.

> > > I've been gathering bits and pieces of information regarding the
> > > packaging of shared libraries for a while now. As I understand it:
> > >
> > > - Normal .so libraries with versioned filenames go into the base package
> > > for a program when they exist
> >
> > Yes.
> >
> > > - Unversioned .so libraries go into the -devel package
> >
> > Yes.

It cannot be answered with a plain "Yes", because such .so files may
be plugins/modules loaded at run-time. Several package submitters
have mispackaged such files because somebody told them that .so would
need to go into -devel packages.

> > > -- If there are no versioned libraries for a program, should a
> > > versioned library be added or should the unversioned .so file be
> > > included in the base package?
> >
> > Option B, I think, but someone else with more insight should chime in. . .

The question is too vague. Does it refer to system libraries? And
does "version" refer to a number in the library SONAME?

Typically, you cannot make up your own versioned library SONAME without
creating incompatibilities. As long as the program authors don't use the
same SONAME together with a sane library versioning scheme, you would
run your own show.
There are approaches that increase the package maintenance requirements
and add incompatibilities, such as building from a libfoo.so (or libfoo.a)
a libfoo-VERSION.so.0, which would require a modification of any app that
linked with plain -lfoo and now would need to link with -lfoo-VERSION.
Contact upstream. Though, it may be that they even refuse to apply
a patch for building a proper shared library, because they want to
continue with changing the API even in minor releases.

> > > - Libraries which are used by other programs at runtime should be
> > > versioned, and in %{_libdir}
> > > -- Are there exceptions to this? When is it appropriate to leverage
> > > subdirectories and /etc/ld.so.conf.d/?

Note that it may be that the upstream distribution does that by default.
It's convenient for any library stack you would want to swap out at run-time
(and with avoidance of file conflicts at install-time).
Think "alternatives" for libraries. Multiple builds of a library with the
same name but different build options or different releases.

> > > - Libraries which are plugins to one specific program, and are dlopened
> > > by that program, do not need a versioned filename. They should go in
> > > their own subdierctory in %{_libdir} (e.g. /usr/lib/gstreamer-0.10)
> > > -- If packaged as seperate plugins, they should be in packages called
> > > packagename-plugins-pluginname, or something similar
> > >
> > > - All shared library filenames should begin with lib

Why?

For example, plugins/modules as well as LT_PRELOADed shared libraries
don't need to begin with "lib".