[PATCH] Use samba-tool to add DNS entries with samba_dnsupdate

Andreas Schneider asn at samba.org
Tue Sep 8 06:59:05 UTC 2015

On Tuesday, September 08, 2015 09:36:57 AM Andrew Bartlett wrote:
> On Mon, 2015-09-07 at 16:46 +0200, Andreas Schneider wrote:
> > On Monday, September 07, 2015 03:45:36 PM Andrew Bartlett wrote:
> > > On Thu, 2015-09-03 at 18:53 +0200, Andreas Schneider wrote:
> > > 
> > > I would review this, but can you please propose a patch with a
> > > clearer
> > > title and rationalle for 'dns faking'.  Can we please define it
> > > 
> > > into:
> > >  - nss DNS emulation
> > >  - resolv DNS emulation
> > 
> > nss DNS emulation is used by most of our code.
> > resolv DNS emulation is only used for SRV lookups.
> > 
> > resolv DNS emulation works only because libresolv is a library on its
> > own and
> > it is using socket function we wrap with socket_wrapper.
> > 
> > getaddrinfo calls gethosbyname3 which comes from libnss_dns.so and it
> > calls
> > __libc_res_nsearch().
> > 
> > Maybe we can intercept __libc_res_nsearch(). I have to play around
> > with it.
> Andreas,
> Thanks for looking into that.  But backing up a little, what of the
> above does 'dns faking' turn on and off?

resolv_wrapper can either direct queries specifying a nameserver in our own 
resolv.conf file or fake it (with a dns_hosts_file). This is only for code 
with uses res_(n)search or res_(n)query e.g. libkrb5 or samba code doing SRV 
record lookups.

All other name resolution is going trough nss_wrapper which wraps 
getaddrinfo(), gethosbyname*() etc.

> For me, we must have a single source of truth for the names, either a
> (single) file, or a DNS server over socket_wrapper.  The part-way
> solutions we have and are being proposed are just messing with my head.
> The challenge I have is that I want to only rely on our DNS server, not
> also the static hosts file.  This is because I want to test changing IP
> addresses and names (which is the client task that triggered all this,
> a tested set of scripts to change the IP and name of a DC).

If you want to support only one resource you should implement support to load 
NSS host modules in nss_wrapper. Then implement a NSS host dns module using 
libresolv or directly dlopen() libresolv_wrapper.so.

This way you only have one source for DNS ...

I'm happy to discuss details and review patches you send for nss_wrapper 


	-- andreas

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