possible patch for implementing split DNS

[Oliver Fromme]

Julian Elischer wrote:
 > I need some processes to look elsewhere for DNS information from where 
 > the rest
 > of the system looks.. This patch seems to me a simple solution.
 > We over-ride where the resolver looks for resolv.conf using an 
 > environment variable.
 > This would allow me to reset this to an application specific config file 
 > that
 > specifies a different server.

I think that could be useful indeed.  In fact it could have
been very helpful to me recently when I had to debug a very
strange resolver problem (it turned out that the DSL modem
dropped SOA and ANY requests).

In theory, there would be a different (and maybe better)
solution to the problem.  On the "FreeBSD Ideas" web page
there is an entry to port variant symlinks from DragonFly
(but as far as I know, nobody is actually working on it).
Using variant symlinks, the problem could easily be solved:

$ ls -l /etc/resolv*
-r--r--r--  1 root  wheel  ... /etc/resolv.conf -> resolv-${RES}.conf
-r--r--r--  1 root  wheel  ... /etc/resolv-default.conf
-r--r--r--  1 root  wheel  ... /etc/resolv-special.conf
$ varsym RES
RES=default
$ cat /etc/resolv.conf
nameserver 11.22.33.44
$ varsym RES=special
$ cat /etc/resolv.conf
nameserver 55.66.77.88

It also has the advantage that the admin still has some
control over it, because the symlink can only point to
existing files under /etc in this case.  By the way, the
varsym variables can be set globally, per-user and per-
process.

However, I'm aware that variant symlinks are probably not
going to be available in FreeBSD anytime soon.  Therefore
I think your patch to libc/net/res_init.c would be useful.

Best regards
   Oliver

-- 
Oliver Fromme,  secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
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