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Date: Sun, 25 Oct 2015 14:06:29 +0100
From: Jan Broer <jasiu.79@...il.com>
To: musl@...ts.openwall.com
Subject: Re: Re: Would love to see reconsideration for domain and search
> 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?
I don't think it is a good idea do default to ndots=0. This would
essentially break search for systems where resolv.conf values are managed
by the DHCP server. DHCP expects search to work when there is at least one
entry in the domain-search option returned by the DHCP server. There is no
DHCP option for configuring ndots (see
http://linux.die.net/man/5/dhcp-options) and therefore search would not
work in these configurations when ndots defaults to 0.
Also, i don't think your argument for setting ndots to 0 by default is
valid:
Search always to be enabled explicitly even when the default for ndots=1:
There is no search unless the user explicitely writes search paths in his
resolv.conf or configures his DHCP client to get the domain-search option
via DHCP.
So the resolvers search functionality is already something the user has to
enable explicitely.
On Sun, Oct 25, 2015 at 12:02 AM, Rich Felker <dalias@...c.org> wrote:
> On Sat, Oct 24, 2015 at 02:33:31PM -0700, Tim Hockin wrote:
> > On Oct 24, 2015 12:20 PM, "Kurt H Maier" <khm@....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
>
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