Re: Improved DNS resolving for laptops?

[Nix <nix at esperi dot org dot uk>]

On Fri, 23 Jul 2004, Paul Jarc mused:
> Petter Reinholdtsen <pere@hungry.com> wrote:
>>  The file /etc/resolv.conf is updated by the DHCP client, but the
>> programs do not re-read this file once they are started.  This is a
>> problem for long-lived programs, and for my laptop this means it is
>> a problem for most programs (hibernate works. :).
> 
> The djbdns client library's approach could be useful.
> <URL:http://cr.yp.to/djbdns/resolve.html>:
>      * Most long-running programs don't notice changes in
>        /etc/resolv.conf; they read /etc/resolv.conf when they start, and
>        they don't reread it until they are restarted. In contrast, the
>        djbdns procedure checks for changes every 10 minutes or 10000
>        uses.

If you don't mind nonportability you could use fcntl (..., F_NOTIFY,...)
to find out the instant resolv.conf is changed. (In practice you'd
probably just set a flag on notification and consult the flag on next
DNS lookup: rereading resolv.conf more often than that is pointless.)

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