Persistent data with KDED (or KIOD) and a KIO Slave?

[David Faure]

On samedi 7 octobre 2017 21:22:42 CEST Mark Gaiser wrote:
> Hi,
> 
> I'm about to experiment a bit with a KIO slave idea [1] I've been having
> for a while.
> 
> I get how a KIO slave works, that's not an issue.
> 
> What i don't get fully is how a KIO slave with persistent storage works
> (say like baloo or stash) where a KIOD/KDED module is required to read from
> the storage.
> 
> How would i make a module that:
> * starts on-demand and stays running for the session lifetime once it's
> started. It should only stop if the session stops or if i tell it to stop.
> I'm guessing this is with "X-KDE-Kded-phase" at 2, but then i still don't
> get where that module is registered, how kded knows about it and - most
> importantly! - what needs to be done to get KDED or KIOD to start it? Is
> that some sort of spacial dbus signal?...

KDED/KIOD modules are plugins (.so with embedded json, installed in the right 
dir for kiod to find it).
Take one example (for kiod: kio/src/kssld; for kded: kio/src/ioslaves/remote/
kdedmodule), do the same :)

> * We have KDED and KIOD, i think i would like to use KIOD for the reduced
> dependency, but is that possible with the requirements of the point above
> this one?

KIOD is only about services started on demand.
Do you really need something that starts with the user session?

> * For persistent storage (or session persistent like for instance the stash
> plugin), what is the best way to get data from the module into the KIO
> slave? DBus? Protobuf? shared memory?

What I don't get is: if it's only about persistent storage, i.e. on disk,
why do you need a kded/kiod module? You could just use the storage from the 
slave, with a lock file.

> [1] At this moment it's for a KIO slave dedicated to tag support backed by
> either a JSON or YAML file and does not require file monitoring at all to
> work.

Then it seems to me you don't need a kded/kiod module.

-- 
David Faure, faure at kde.org, http://www.davidfaure.fr
Working on KDE Frameworks 5