Re: Re: Would love to see reconsideration for domain and search

[Rich Felker <dalias@libc.org>]

On Sat, Oct 24, 2015 at 02:33:31PM -0700, Tim Hockin wrote:
> On Oct 24, 2015 12:20 PM, "Kurt H Maier" <khm@sdf.org> wrote:
> >
> > On Thu, Oct 22, 2015 at 02:24:11PM -0700, Tim Hockin wrote:
> > >
> > > I understand your point, though the world at large tends to disagree.
> >
> > The world at large uses bad software.  Please don't use this sort of
> > reasoning as a justification for and embrace-extend operation on actual
> > standards.
> 
> Where is the standard that defines ordering semantics in resolv.conf?

I don't think it's useful to argue about intent unless someone wants
to dig up history and find out what the original implementors
intended, and even then it's rather arbitrary whether people would
care about that intent since it doesn't seem to have been documented
explicitly. My view is that it's more useful to consider the
consequences of both interpretations and draw a conclusion that one
should be preferred from the bad consequences of the other.

> > > The real world is not ideal.  Not all nameservers are identically
> > > scoped - you MUST respect the ordering in resolv.conf - to do
> > > otherwise is semantically broken.  If implementation simplicity means
> > > literally doing queries in serial, then that is what you should do.
> >
> > You absolutely cannot respect the ordering in resolv.conf; at least not
> > if you're relying on someone else's resolver.  If the orchestration
> > software depends on specific results being returned in particular
> > orders, the orchestration software should provide a mechanism to
> > generate them.
> >
> > > Similarly, you can't just search all search domains in parallel and
> > > take the first response.  The ordering is meaningful.
> >
> > It should not be, and more to the point will not reliably be,
> > meaningful.
> 
> Search has to be ordered.  You can not possibly argue otherwise?

Indeed, search certainly has to be ordered. Otherwise results are most
definitely non-deterministic. The trivial example would be looking up
"www" with 2 or more search domains.

In any case, it was discussed way back that, while parallel search
could be implemented as long as a result from search domain N is not
accepted until negative results from domains 1 to N-1 are received,
the implementation complexity cost was too high relative to the value
of such a feature.

> > You are arguing for introducing performance penalties into musl that do
> > not affect you but do very much affect lots of other users.  I hope they
> > do not happen -- musl is not the right place to fix your problem.
> 
> I am arguing for adding a very standard feature (search) to open musl to a
> whole new space of users. Nobody is forcing you to use search paths or
> ndots.

The only place adding search support might negatively impact existing
musl users is by causing hostnames with no dots to be queried with the
(often useless and unwanted) default domain set by dhcp before
failing. My preference would probably be having musl default to
ndots=0 rather than ndots=1 so that search has to be enabled
explicitly. Are there any reasons this would be undesirable?

Rich