Debian Bug report logs - #820056
same file in multiple views breaks in 9.10 -- writable file 'foo': already in use

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Message #5 received at submit@bugs.debian.org (full text, mbox, reply):

From: sacrificial-spam-address@horizon.com

To: submit@bugs.debian.org

Cc: sacrificial-spam-address@horizon.com

Subject: writeable file 'foo': already in use

Date: 5 Apr 2016 00:06:54 -0400

Package: bind9
Version: 1:9.10.3.dfsg.P4-6
Architecture: i386
Severity: important

Discussion of this issue can be found at
http://bind-users-forum.2342410.n4.nabble.com/Single-slave-zone-definition-for-two-view-cache-file-name-problem-td12.html
https://www.linuxquestions.org/questions/linux-server-73/bind-9-10-same-zone-in-two-views-4175572231-print/

Like many people running split DNS (multiple views), a large number
of my zones are common to the two.  So when setting this up, I did the
obvious thing:

zone "internal" {
	match-clients { ... };
	recursion yes;
        include "/etc/bind/named.conf.default-zones";
        include "/etc/bind/zones.rfc1918";
	include "/etc/bind/named.conf.common";

	/* Zones private to this view */
};

zone "external" {
	match-clients { any; };
	recursion no;
        include "/etc/bind/named.conf.default-zones";
        include "/etc/bind/zones.rfc1918";
	include "/etc/bind/named.conf.common";

	/* Zones private to this view */
};

Where named.conf.common contains various zones my name server
is authoritative for, and some zones it is secondary for like like:

zone "foo" {
        type slave;
        file "/etc/bind/cache/db.cache.foo";
        masters { foo_name_servers; };
        allow-transfer { any; };
};

While comments from the BIND maintainers suggest that it may have been
buggy, it was a sensible thing to do and worked for many years.  BIND 9.10
now detects this and fails to start, producing error messages like:

Apr  4 20:55:00 ns named[27115]: /etc/bind/named.conf.common:81: writeable file '/etc/bind/cache/db.cache.foo': already in use: /etc/bind/named.conf.common:81

Needless to say, named not starting leads to complete DNS failure and
is a pretty unhappy state to upgrade to.  (Thus the "Severity: important".)

At first, I thought this was a bug (how can a config file line conflict
with itself?), but then I realized that the conflict was between the
two views.

There does not appear to be any simple workaround.  The best solution
appears to be to use the new BIND 9.10 "in-view" feature, which allows a
zone in one view to be a reference to the same zone in a different view.
When this is done, both views may share the same cache file.

The down side is that this violates one of the important principles of
programming: only specify something in one place.  Instead, I have to have
a "master" definition and several "in-view" declarations referencing
the master.

I wish BIND would either deal with the problem after noticing it (by
automatically doing the equivalent of the in-view), or provide a way to
import every zone in a view, avoiding the need for a long list of in-view
declarations.


In case it helps anyone else, here's my current workaround:

One file declares a non-published view "common" as follows:

view "common" {
        match-clients { none; };

	zone "foo" {
		...
	};
	...
};

Then I use the following sed script on that file (which relies on each
"zone" header being on a line by itself, preceded by a tab)

# Script to convert each zone in a view to a series of in-view declarations
1i\
	// Automatically generated by Makefile and in-view.sed\
	// MANUAL EDITS WILL BE LOST
/^	zone/{
a\
		in-view "common";\
	};
p
}

And I created a Makefile that applies the recipe
	sed -n -f in-view.sed $< > $@
to produce a series of references that can then be included within
each view:

	zone "foo" {
		in-view "common";
	};

Message #12 received at 820056@bugs.debian.org (full text, mbox, reply):

From: Bernhard Schmidt <berni@birkenwald.de>

To: sacrificial-spam-address@horizon.com, 820056@bugs.debian.org

Subject: Re: Bug#820056: writeable file 'foo': already in use

Date: Wed, 13 Dec 2017 15:57:02 +0100

Control: tags -1 + upstream wontfix

On Tue, Apr 05, 2016 at 12:06:54AM -0400, sacrificial-spam-address@horizon.com wrote:

Hi,

> Discussion of this issue can be found at
> http://bind-users-forum.2342410.n4.nabble.com/Single-slave-zone-definition-for-two-view-cache-file-name-problem-td12.html
> https://www.linuxquestions.org/questions/linux-server-73/bind-9-10-same-zone-in-two-views-4175572231-print/

> While comments from the BIND maintainers suggest that it may have been
> buggy, it was a sensible thing to do and worked for many years.  BIND 9.10
> now detects this and fails to start, producing error messages like:

As written there, this has been a concious decision by upstream. We will
not revert this locally.

Bernhard

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