On 29/09/2015 04:46, Casper Ti. Vector wrote:
Nevertheless, I think it can be helpful to also support "opportunist" dependencies: if said service is not enabled, it is silently ignored; if said service is enabled, the dependency on it is considered in the dependency resolution process.
As you subsequently wrote, this can be left out of s6-rc. An "opportunist" dependency is not a real dependency, since the service can start without it; if you want to include it, a preprocessor for source directories is the exact right thing to use.
* Online `OR'/virtual dependencies: (...) For example, with a laptop, it's common and useful to have `eth0' and `wlan0' both providing network access, and a network-dependent service can start when either is up.
That kind of dependency is still infrequent compared to "normal" dependencies; I don't think it's unreasonable to maintain a set of compiled databases to address that case. The size of the set may grow exponentially, but if it becomes larger than 4 or 8 databases, I tend to think it's an abuse of virtual dependencies; I can be convinced otherwise with a real-world example that cannot be solved another way. Having several compiled databases and switching between them with s6-rc-update is normal procedure. I worked on s6-rc-update for a long time to make sure that this procedure would be as painless as possible, even if it has to be done on a semi-regular basis. Switching between eth0 and wlan0 is a typical case of this, and as a matter of fact, it's *exactly* what I'm doing on my home router. :) -- Laurent
