[libvirt] [RFC] net-dhcp-leases: Query: Reg: Leases API Script

[Nehal J Wani]

On Tue, Oct 22, 2013 at 9:10 PM, Eric Blake <eblake at redhat.com> wrote:
> On 10/22/2013 04:15 PM, Daniel P. Berrange wrote:
>> On Tue, Oct 22, 2013 at 04:15:37PM +0530, Nehal J Wani wrote:
>>> Q1. The --dhcp-script option will require libvirt to provide a script
>>> or executable file to be run. Now as the man page says, this file is
>>> executed "Whenever a new DHCP  ease is created, or an old one
>>> destroyed". Life was easy with the script, as it used the command sed
>>> to remove the destroyed lease. eblake had suggested me to use a C
>>> program instead. So I wanted to finalize whether to go with C or
>>> continue with shell script.
>>
>> Libvirt aims to avoid shell code whereever possible, since it is really
>> a very bad language from terms of reliability and security. eg quoting
>> rules are easy to get wrong, error handling is awful, portability is
>> non-trivial.
>
> For examples of writing a helper C program, see how src/util/iohelper.c
> is compiled into libvirt_iohelper.
>

What are libvirt's views on python as a helper program?

>>
>>> Q2. The above executable file will be writing the custom formatted
>>> lease parameters to a file "dnsmasq-ip-mac.status" (suggestion open
>>> for name). This newly created/updated file will be parsed by the API.
>>> We need to decide the format for the file. Do we continue with space
>>> separated parameters as before?
>>
>> Ideally do not invent any new format - use a format that we already
>> have a parser for - eg the src/util/virconf.h or src/util/virkeyfile.h
>> APIs for loading configs.
>
> or XML, if the config file format is insufficient.
>

Actually, the leases file generated by dnsmasq follows the format of
space separated parameters (For which I had created a parser in the
earlier versions of the patch). But considering the fact that each
time the script is called, in case the first argument is "del" or
"old" I'll need to replace the existing lease with the new one, for
which I am a bit confused as to which format should be followed and
whether it would be easier to code it in C (I can't think of anything
easier than loading the whole file into buffer and then replacing the
corresponding line, and then writing back to the file { Hoping that
existing semaphores will take care of the reader-writers problem :) }
). Is life more easy handling XML, or ini-style formats (using the
existing helpers)?

> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>



-- 
Nehal J Wani