Comment 0 for bug 1575200

I've discovered a problem in lightdm XDMCP using link-local IPv6 addresses without interface index to connect to X server.
It has been originally reported at https://bugzilla.redhat.com/show_bug.cgi?id=1322775.

The problem can be fixed by having the XDMCP client not transmitting link-local addresses in the request, but if it does, lightdm XDMCP server can be a lot smarter if the attached patch is applied.

It changes the X server address selection order to set the lowest preference to link-local addresses, even if matching the source address or family.

This is not 100% full-proof: if only link-local addresses have been received, one of them is used anyway. In this case, a complete solution would be to determine and set the address interface index if not ambiguous.

However, this patch fixes the problem for most of the non-pathological
cases.