Re: [Libvir] RFC: Broadcast our presence with avahi

All the really trendy network services these days broadcast their presence on the LAN using mDNS. In Linux world this means becoming an Avahi client and registering our services. virt-manager is also able to become an Avahi client and browser for services. So you'll be able to let the user just pick a host straight off a list instead of typing in hostname.

The attached patch does two things: - Extends our event loop implementation so it can modify the event mask associated with an FD, and the timeout associated with a timer. While you could simulate this with an add & remove, this has the possibility of failure (from malloc). Merely updating an existing event can be done without failure. Avahi needs this ability for its event loop integration - Added qemu/mdns.c file to actually provide the service information. This has two parts. The first section of code is taken straight from one of the Avahi example programs. The second section is a implementaiton of the Avahi event loop contract in terms of our event API - it works very nicely which says good things about design of our event loop Some things... - I arbitrarily picked a service type of '_libvirtd._tcp'. The docs on picking service types seem non-existant on Avahi website, but it seems to be common to use service name from /etc/services and protocol both prefixed with _. - I advertise two subtypes, of '_xen.libvirtd._tcp' and '_qemu.libvirtd._tcp' What I actually want todo is to be able to probe the libvirt local drivers to auto-discover what virtualization platforms are available. A sort of lightweight virConnectOpen which merely returns TRUE/FALSE and doesn't actually allocate a virConnectPtr object. Need to extend the internal driver API for this. - I want to advertise whether the server is configured with TLS certs or not, so remote clients can automatically choose to use SSH urls with the remote driver if neccessary. - Let the admin turn advertisement on/off in the config file because some people may not like it on their LAN. If you fancy trying it, avahi-browse --all from another host on the LAN should show the service being advertised. The advertisements do not cross LAN routers by default.