[Xcb] [ANNOUNCE] xcb-util 0.3.9

Jeremy Huddleston jeremyhu at freedesktop.org
Mon Jun 4 16:24:10 PDT 2012

On Jun 4, 2012, at 3:25 PM, Josh Triplett <josh at joshtriplett.org> wrote:

> On Mon, Jun 04, 2012 at 02:52:51PM -0700, Jeremy Huddleston wrote:
>> On Jun 4, 2012, at 2:19 PM, Adam Jackson <ajax at redhat.com> wrote:
>>> On Mon, 2012-06-04 at 14:03 -0700, Jeremy Huddleston wrote:
>>>> On Jun 4, 2012, at 1:34 PM, Julien Cristau <jcristau at debian.org> wrote:
>>>> Think about this from the libc perspective.  libc *may have* strlcat
>>>> or not, but they're named the same because all functions in libc have
>>>> consistent signatures.
>>> A libc that had strlcat once, and then removed it, would no longer have
>>> the same ABI.  An application that had successfully linked against the
>>> old libc's strlcat would reasonably expect it to be present at runtime
>>> too.
>> That argument breaks down when you reverse it.  The "rules" state that the SONAME should not change when adding APIs.  If all you're basing this on is SONAME, then there is absolutely no difference between the adding and removing case.  If I link against a "newer" libc which has strlcat, then by your argument, I'd expect strlcat to be present on any libc matching that SONAME.  When I run my application with the older libc without strlcat, it will fail to find it.
> That represents the difference between major and minor version changes.
> When you add a new function (or otherwise extend the ABI, such as by
> adding new flags to a flags parameter), you increase the minor version,
> so that applications built against the new library won't run with the
> old one, but applications built against the old one (and thus not
> expecting the new function) will still work with the new library.
> However, when you *remove* a function, applications built against the
> old library will not work with the new one, so you have to bump the
> major version.

I guess this is where the "OS X" paradigm and the GNU paradigm just break down.  Is there actually annotation done to specify that a specific function was added for a given minor version bump of a library?  Does the loader just require that the runtime version be >= the linktime version (that seems particularly dangerous to me)?  How is this actually enforced in practice?  My understanding was that the minor version was nothing more than extra bits as a guide to the user or packager and that there wasn't actually any "real" mechanism in place to deal with this properly (ie weak linking the new symbols).

>> SONAME is not the solution to this problem.  The best practice is to properly annotate "new" functions (so they are weak linked) and not remove public API until it is really warranted.
>> If you're removing a fringe API that is only used internally, then I'd argue against SONAME change.
> Only if you know for sure that it won't break any real applications; in
> other words, does this represent de-facto public API, or not?

Based on the commit logs, I was under the impression that these functions were only meaningful to already-removed functionality.  If the removal of that functionality didn't even warrant a version bump, why would removing its support APIs?

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