[Dnsmasq-discuss] dumping current dhcp leases without always updating the leasefile curing normal ?

[Dave Taht]

On Mon, Oct 14, 2013 at 9:42 AM, Simon Kelley <simon at thekelleys.org.uk> wrote:
> On 11/10/13 16:37, Rick Jones wrote:
>>
>> On 10/11/2013 07:16 AM, Simon Kelley wrote:
>>>
>>> On 11/10/13 01:39, Rick Jones wrote:
>>>>
>>>> I am still on the steep learning slope for dnsmasq. The manpage lists a
>>>> -l/--dhcp-leasefile option into which dnsmasq will store lease
>>>> information. I gather though that it will be updating that all the time
>>>> as leases come and go.
>>>>
>>>> Is there a version post 2.59 where one can send dnsmasq a signal to
>>>> cause it to dump a copy of its current lease information to a file, but
>>>> without the continuous updates in normal operation?
>>>
>>>
>>>
>>> No. there's a mode meant for use on flash filesystems that updates the
>>> lease file less often, if that helps.
>>
>>
>> It might actually. I'll try to take a look at it.
>>
>>
>>> See also this thread
>>>
>>>
>>> http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2013q3/007555.html
>>>
>>
>>  From that I should take away that the lease file format is not fixed
>> and there but for the grace of the developers go I should I start
>> grubbing through it, yes? I can accept that.
>>
>>> More context about what youre trying to achieve would help.
>>
>>
>> What I would like to be able to do is "know" (make an informed guess)
>> which of the clients which could have a lease probably have a lease (or
>> probably do not have a lease), but in an environment where I might have
>> either rather busy dnsmasq processes, or a large number of individually
>> not very busy dnsmasq processes and want to minimize the storage load.
>> But I don't need to know all the time, just occasionally and not
>> necessarily on a schedule and not necessarily all the dnsmasq processes.
>> So, I figured some sort of "dump your current leases" feature would
>> satisfy that.
>>
>> I cannot really rely on the clients being willing to respond to the
>> likes of ping, they may only respond to things they've initiated
>> themselves. I also do not have other access to the clients (eg their
>> console). So, all I can think of presently is trying to ask the dnsmasq
>> process(es) what it believes its active leases happen to be.
>>
>> thanks,
>>
>> rick
>> BTW, sorry about botching the last part of the subject there.
>>
>
> You could achieve the two aims "minimise storage load" and "know about
> dnsmasq leases" by implementing the lease database in some sort of
> lightweight database. Dnsmasq is designed so it can be without a lease file
> completely. At startup you prime the in-memory copy of the lease database
> via a DHCP-script "init" call, and then whilst dnsmasq is running is makes
> calls to the DHCP script as the data changes which can be used to update the
> database.
>
>
> Cheers,
>
> Simon.
>

There are also hooks for lua.