code duplication in ccan (was: Re: snprintf on SunOS)
jelmer at samba.org
Thu Jun 21 09:49:26 MDT 2012
On Mon, Jun 18, 2012 at 09:46:32AM +0930, Rusty Russell wrote:
> On Fri, 15 Jun 2012 01:10:01 +0200, Jelmer Vernooij <jelmer at samba.org> wrote:
> > On Thu, Jun 14, 2012 at 06:57:30PM -0400, simo wrote:
> > > I am really oppoe to make samba-util a dependency for tdb, samba util is
> > > in NO shape to become a real public library. Let's not do the worst
> > > thing we could please.
> > I wasn't saying anything about making it public. ccan already *is* a
> > dependency of tdb and it's not public either. Neither is a great
> > situation.
> BTW, you mean ntdb/tdb2, not tdb?
> But yes, lots of confusion here. Technically, CCAN is built as a shared
> lib (not for any good reason), but it's also linked directly into
> libtdb2/libntdb as it's a private dependency.
> It's not *public*, that would be wrong.
There is cost and value associated with putting things into a
shared library rather than just copying the code (be it source or
binary) into lots of different places.
> > It would be nice to make samba-util public, but that would (as you
> > said earlier) require some effort to clean it up and define a
> > stable API.
> Nice? It's a terrible idea!
> Why is public better than private? More maintenance overhead for us,
> more bloat and cruft as we can't remove old APIs, and it's not like
> anyone else is going to use libsamba-util.so.
Sure, it has its disadvantages. You have to be careful what you
declare stable and public. The various bits in samba-util haven't
changed in a long time though, and they are all pretty independent.
I'm not proposing making them public in their current form, we can
clean them up first and cherrypick.
The cost of changing a public ABI isn't just in maintaining backwards
compatibility; like any API change (private or public), all existing
call sites will also need to be updated.
openchange has been using some of these libraries for a
while, even though they have only been semi-public. We originally
started installing these headers files so OpenChange could link
against Samba 4 rather than be a fork of it. For example, our
pidl-generated DCE/RPC code (which OpenChange uses) uses some of these
The alternative is including these lumps of code in each of the
generated files, or have openchange ship its own copy.
That has got its disadvantages too. Changes are only made in one
copy (e.g. bug fixes); you have to make sure the symbols don't clash.
If there are data structures that are part of the ABI you need to make
sure that those created by the Samba version of your utility code
never end up in the OpenChange version, ...
> If you insist on making everything shared a public shared library, you
> end up with coders cut & pasting to avoid the hassle. That's what tdb
> did: cut & paste the hash code :(
Hasn't that already happened? My impression of ccan is as a repository
with little snippets of code that coders can copy-paste into their
source to reuse. Is that an incorrect view of it?
I'm not advocating making every single function in Samba public, nor
am I advocating branding samba-util's existing semi-public API as stable.
I'm not insisting on making everything shared a public shared library.
But samba-util is already public to some degree, and changes to the
ccan ABI have an impact too (see my other email).
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