- Alternatively, have two different files implementing the same
- interface, and choose either the new or the old API. This is
- probably necessary for systems that e.g. have IPv6, but
- gethostbyaddr() can't handle it. The Linux manpage claims this is
- currently the case.
+Handling IPv6 on old machines
+
+ The KAME IPv6 patch is nice in theory but has proved a bit of a
+ nightmare in practice. The basic idea of their patch is that rsync
+ is rewritten to use the new getaddrinfo()/getnameinfo() interface,
+ rather than gethostbyname()/gethostbyaddr() as in rsync 2.4.6.
+ Systems that don't have the new interface are handled by providing
+ our own implementation in lib/, which is selectively linked in.
+
+ The problem with this is that it is really hard to get right on
+ platforms that have a half-working implementation, so redefining
+ these functions clashes with system headers, and leaving them out
+ breaks. This affects at least OSF/1, RedHat 5, and Cobalt, which
+ are moderately improtant.