On Fri, Sep 19, 2008 at 12:39:41PM -0400, Simo Sorce wrote: > Both API and ABI compatibility are important.
Yes. > API compatibility is more important for developers. I don't quite agree. Developers who distribute binaries want their binaries to run. They also want their code to remain buildable. See below. > ABI compatibility is more important for system administrators. And users, and developers. See above. Also, in practice ABI compatibility makes API compatibility very likely, with at most minor source changes needed if the API is changed incompatibly. Changing, e.g., a typedef *may* be source-incompatible, but binary compatible. Whereas focusing on API compatibility alone often leads to ABI incompatibilities. E.g., changing a struct size/layout -> API compatible (sources rebuild), ABI incompatible (assuming the struct's size/layout is part of the ABI). We (Sun) are more cavalier (though far from careless) about API compatibility than ABI. Our compatibility guarantee is, after all, a *binary* compatibility guarantee. If your vendor/distro maintainer doesn't do the same for you, forcing you to rebuild everything periodically, then you're likely to care about source compatibility a lot more. > THe important thing is to reach a decent balance and make sure ABI/API > breaks happen on a major release and they are very well advertized in > advance, so that vendors can plan how to address the issue. The MIT krb5 has not had a well-defined API. Therefore MIT has focused on ABI compatibility: if something breaks binary compatibility, they'll fix it. In fact, though the Consortium appears to be making progress w.r.t. API documentation, until the API is fully documented then the Consortium has no choice but to focus on ABI compatibility. Nico --
