Re: [libvirt] RFC: 'old' event for leaseshelper.c when lease renews

In the current version of dnsmasq, the leases helper script/program specified by --dhcp-script to dnsmasq is invoked on three events, 'add', 'old', 'del'. In short, add: -> a new lease has to be added to db del: -> a lease has to be deleted from db old:-> if lease has changed Now, the lease can be considered to be changed in 2 ways. [standard-change] The change could be to the associated hostname or MAC address [auxiliary-change] The change associated with expiry time or clientid When only --dhcp-script is set, 'old' events are sent only for standard-lease changes. But when --dhcp-script is set along with --leasefile-ro, 'old' events are sent for any change in the lease. So, right now, if a lease is renewed, the reflected change doesn't appear in our JSON formatted lease database <interface-name>.status. We have the following options with this: (i) We can simply add the --leasefile-ro option. But in that case, the leases file database which is generated by dnsmasq by the name <network-name>.leases will cease to exist. It won't contain any lease information. All lease database handling will be done by our leaseshelper. Note: this option given a lot of information which is not stored in <network-name>.leases file.

(ii) We ask the dnsmasq developer(s) to add an extra command line option to enable auxiliary changes in lease to be propagated to leaseshelper via 'old' events. I had a small conversation with Simon Kelley, and he said: "Yes. For that application (libvirt), you clearly don't want a third-party patch. At very least I'd be willing to add a boolean option to dnsmasq which enables "old" events when the lease expiry time changes, independent of leasefile-ro." If we do this, then can retain <network-name>.leases and have our helper too.