[Dnsmasq-discuss] rereading configuration files

[Ed W]

On 24/10/2012 18:59, Dan Williams wrote:
> On Tue, 2012-10-23 at 20:42 +0100, Simon Kelley wrote:
>> On 23/10/12 20:21, Gene Czarcinski wrote:
>>> It would be useful to libvirt if dnsmasq would reread the configuration
>>> file and/or the files in the configuration directory upon demand (via
>>> SIG<something>) as is done for some other files.
>>>
>>> Right now, when minor changes are made to a network configuration, it is
>>> necessary to restart dnsmasq to get those changes adopted.
>>>
>>> Is this a possibility this could be done or is this one of those things
>>> that yes, it could be done, but it would require rewriting most of
>>> dnsmasq. What types of changes might be accommodated? What if these
>>> changeable definitions were put into a special configuration file?
>>>
>>> Example: v6 or v6 dhcp-range.
>>>
>>> Example of something that would unlikely be possible: interface=
>>>
>> The most difficult problem is that dnsmasq throws away root permissions
>> after start-up, so re-reading the configuration is impossible if acting
>> on the new configuration involves anything that needs root (for
>> instance, binding sockets to ports <1024 or opening the lease file.)
>>
>> The philosophy is that things that would be really useful to change,
>> without restarting dnsmasq, and certainly don't need root, are re-read
>> on SIGHUP. That's dhcp-host information and dhcp-option information in
>> special configuration files, /etc/hosts and /etc/ethers, and possibly
>> /etc/resolv.conf, if it's not being polled anyway.
>>
>> For anything else, restarting dnsmasq is a pain-free operation anyway:
>> there's very little state and nothing important is lost over a reboot.
> One problem we ran into with NM, and why I posted the patch for the new
> D-Bus interface call, was that updated DNS configuration is *not*
> re-read on HUP.  That means that whenever we change nameservers as a
> result of DHCP renewal, connection of a VPN, or some other thing that
> updates DNS, we need to either (a) use the D-Bus interface or (b)
> respawn dnsmasq.  Unfortunately there's a small window when respawning
> dnsmasq where name queries could get lost or prematurely terminated, and
> that's actually been a problem in the real world.  In these cases we're
> running dnsmasq as a local caching nameserver, so
> re-reading /etc/resolv.conf would only ever return 127.0.0.1 and thus
> that part isn't relevant.
>
> Obviously if we're using D-Bus now this isn't a problem, but might be
> worthwhile to re-read DNS server/domain info on HUP to for other users.
>
> Dan
>
>
>

Is the answer then to always use dbus?  Openresolv I think uses dbus in 
this way when reloading data due to interface changes - is it not 
handling things in the desired way?  If so could you use it's technique?

     http://roy.marples.name/projects/openresolv

Cheers

Ed W