[pkg-kde-talk] Re: kdnssd and avahi/libnss-mdns

[Jakub Stachowski]

Dnia wtorek, 17 stycznia 2006 18:24, Lennart Poettering napisał:
> On Wed, 18.01.06 03:23, Anand Kumria (wildfire at progsoc.org) wrote:
> > > kdnssd needs avahi-daemon to function at all. avahi-daemon recommends
> > > your libnss-mdns;
> >
> > avahi doesn't need libnss-mdns, and nor does libnss-mdns but if both are
> > installed libnss-mdns will use avahi for caching purposes.
> >
> > You want to have libnss-mdns installed for applications which may not
> > (indeed ever) link directly to avahi, e.g. telnet; that way things like
> > 'telnet foo.local' will work.
>
> I don't know how kdnssd works internally, but it might *require*
> libnss-mdns to work sensibly. Better ask Jakub Stachowski about
> that. I'll forward this Email to him.

For discovering services it won't do too much without libnss-mdns because 
kdnssd-avahi does not even try to resolve hostname.local address and just 
hands it to application. Without libnssd-mdns application won't be able to 
resolve it.

>
> > > presumably these two packages would be a sensible core
> > > zeroconf setup for kdnssd to depend on (right?). libnss-mdns recommends
> > > the package 'zeroconf' as well. It runs in the background, which is
> > > something I'd rather not have too many packages do, if they're not
> > > critical; but libnss-mdns does recommend it... what do you suggest?
> >
> > well 'zeroconf' performs the link-local address allocation, which you
> > definately need.  I have a 0.7 version that I'm testing that
> > should address most of the current bugs against it.  I hope to have it
> > ready to upload later this week.
>
> I don't think kdednssd should depend on "zeroconf". If it all, a
> Suggest or Recommend should suffice.
>
> In addition I don't think that kdednssd should depend even on
> avahi-daemon. The avahi client libraries return a proper error code
> when no running daemon is found, so in case kdednssd becomes a hard
> dependency of the KDE desktop and people don't like DNS-SD, they don't
> need to install the daemon.

True. All publishing/discovery operations will just report failure and that's 
all.
>
> > > Any other packages we should Depend/Suggest/Recommend? avahi-dnsconfd,
> > > etc.? Any advice would be much appreciated.
>
> My suggestion is to depend on avahi-client. And suggest/recommend
> avahi-daemon and libnss-mdns. However, since avahi-client recommends
> avahi-daemon, and avahi-daemon in turn recommends libnss-mdns you may
> even omit those suggest/recommend lines entirely.
>
> Hence i would suggest to just add a dependency to avahi-client and
> that's it.
>
> (Unless Jakub says that libnss-mdns is required for avahi-kdnssd to
> work properly, in which case you should add another hard dep on that.)

I'm not sure about Depends and Recommends policy but applications using  
kdnssd-avahi will be really crippled without libnss-mdns - they won't be able 
to use discovered services at all.

>
> > > One last thing you might know about.
> > > http://wiki.kde.org/tiki-index.php?page=Zeroconf+in+KDE states
> > > that /etc/nsswitch.conf should have 'mdns' on the hosts line _before_
> > > 'dns'. Yet on my system, mdns comes _after_ by default (this was added
> > > due to bug #324954. Is this a problem?
> >
> > Well, I think it should be:
> >
> > hosts: file mdns dns
>
> I think it should be "file mdns4 dns". Someone should file a bug about
> this.
>
> > because this prevents the local DNS from seeing queries to the '.local'
> > zone; however it could slow things done as the NSS sub-system waits for
> > mdns to return a response (which, from memory can take 3 seconds).
>
> By default, nss-mdns will only lookup services in the ".local"
> zone. Hence this would not result in any significant delay for normal
> (unicast DNS) name lookups.

And in my case (slow link) it helps to avoid unicast DNS questions for .local

>
> Lennart