Date: Fri, 09 May 2014 18:04:08 -0700 From: Andy Lutomirski <luto@...capital.net> To: musl@...ts.openwall.com Subject: Re: Resolver overhaul concepts On 05/04/2014 09:24 AM, Rich Felker wrote: > On Sun, May 04, 2014 at 05:07:33PM +0100, Laurent Bercot wrote: >> >> I believe the very first thing to address is what exactly you call >> a resolver. > > There are some legacy dn_*/res_* interfaces in demand which are > presently supported only poorly or not at all. Part of the side goal > of the resolver overhaul is to provide them cleanly without code > duplication. But for the most part, "resolver" means "getaddrinfo" > since it is the only standard, non-deprecated interface to name > resolution. > >> getaddrinfo() is a horrible interface, and one of the reasons why >> is that it is loosely designed. Not much is standardized, and it's up >> to you to decide exactly what to do with it; it's important to be >> clear about what is implemented, and to document it, because not all >> applications have the same expectations, and it's very easy to get >> confused when the resolution path is unexpected. > > It's standardized by POSIX, and the POSIX text is sufficient to tell > you how to use it for all portable usages. Most of the confusion/mess > comes from non-conforming implemnentations, particularly in the area > of returning wrong error codes. > >> glibc's getaddrinfo() is the entry point to the NSS layer, which >> can basically implement *any* kind of "name resolution". AFAICT, >> it's not a goal of musl to reimplement the whole NSS spaghetti >> monster, but some applications will depend on /etc/nsswitch.conf >> or something similar; even without supporting /etc/nsswitch.conf, >> it would be nice to provide a mechanism to selectively enable/disable >> at least /etc/hosts lookup and DNS lookup. The current resolution > > The policy for supporting something like nss has always been that musl > implements a perfectly reasonable public protocol for providing any > back-end you want: the DNS protocol. You can run a local daemon > speaking DNS and serving names from any backend you like, and this is > the correct way to achieve it (rather than linking random buggy, > likely-not-namespace-clean libraries into the application's address > space). In order to make this the most useful, though, musl should > support nameservers on non-default ports (is there a standard syntax > for this, or can we support one without breaking anything?), and it > would also be nice to be able to override resolv.conf on a per-process > basis (e.g. via the environment). How about 'nameserver /path/to/unix/socket'? If glibc supported that, too, it might solve a lot of problems involving systemwide resolvers and containers. This might have to be 'unixsocknameserver /path/to/unix/socket' or something for better interoperability. --Andy
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