Several use-cases of dbus

[Dmitry Morozhnikov]

Hello all!

I`m plan to begin some hacking to make my desktop better as i see it (usually, 
it is too difficult to describe what i wish to see than implement it by 
self..) Generally, i`m not happy with current state of system-service/desktop 
interoperability. And after some looking at this list i think what dbus is an 
only right solution in that area.

But first of all, please correct my main assumption: per-login dbus daemon 
connects to system dbus daemon and able to to and from it. (Unfortunately, i 
was not found answer to this question after looking at documentation and 
first-time looking at the code).

1.

Well, lets imagine first simple situation. Some service, say, hypothetical 
virus scanner fired up by cron at some time. In my meaning desktop user 
_should_ have been noticed about that. How it can be done. 

Service on startup connects to system dbus and fire up broadcast notification. 
In simple meaning, this service can`t and should no know who is logged in on 
desktop, how much users logged in if any. So it can`t ask desktop dbus daemon 
to start notification process. It just fire up notification about "Super 
virus scanner is working". But who will listen for such messages?

I think there should be special per-login daemon which will serve such 
notification. Name it.. DesktopAgent (and interface, therefore will be 
something like org.freedesktop.dbus.desktopagent). After receiving 
notification from service, it should:

1) Check if current user have some level of access to this specific service. 
How? I don`t know.. Maybe check user/group of runned service and check user 
permissions? Looks like transparent solution, but i`m not sure if this 
possible with dbus at all.
2) If yes, select appropriate applet which is shipped with this specific 
service and ask desktop dbus daemon to run it. Maybe service can provide 
well-known name of such applet, so work of DesktopAgent will be pretty simple 
in this case.

After that, in tray icon will appear some sign of runned service. User will be 
able to control or ever stop it. But that part should be completely 
applet-depended, i think.

Is it possible to implement DesktopAgent functionality into per-login dbus 
daemon? Yes, but i`m very unsure what this is good idea.

2. 

Okay. Let`s imagine more complicated example. Super virus scanner was started 
at 10:00 am as expected, but.. user, after two cups of coffee, reach computer 
at 10:05 am. How it will know about runned service if DesktopAgent have no 
chance to receive notification from it?

In my opinion, DesktopAgent just after startup should fire up broadcast 
message, something like "Please renotify me" which will cause all services 
interested in it resend notifications "I`m there". Probably, such operation 
should be repeated each five minutes or so, to avoid message lost, etc..

3. 

Continuing with virus scanner. Today, it is possible to intercept file system 
access to some infected file and do some action on it (dazuko project for 
example). But user have no chance to interact with anti-virus software to 
tell it which action should be performed. Okay, having DesktopAgent and 
antivirus which can interact with it, it is possible to run special applet to 
ask user a question (delete, quarantine, heal, ignore, etc..). But.. What if 
there are no one near the computer? How long service should wait to perform 
default action? And most important question in our context: should it be 
notified if question dialog is appear to the user at all?

4.

Last scenario i can remember now :-)

Some dialup service is issued to run by kmail for example. Unfortunately, 
modem is busy for a moment by ifmail (there are few peoples who know what is 
that, but it is not meaningful :-). Kmail uses dbus to perform this action 
and receive negative response immediately. But other peoples logged it also 
want to know about this error! And yes, it is pretty possible to create 
another special applet, specific to this dialup service which will display 
error and exit. But may be it is more simple to allow DesktopAgent to respond 
by self for some specific action like system error messages? Any ideas?

P.S. Please forgive me if my questions are completely stupid or there is 
already some projects with such purpose. Unfortunately, i can`t start work 
right now, but i want to have some food for the thought now. I`m not sure if 
this is possible at all with dbus or if this feet dbus design/purpose at all.

P.P.S. Please, if this possible don`t tell me "noone need such antivirus under 
linux". This is not an answer. After last fight with Gaelitum.A under windows 
i`m a little paranoid about that. Anyway, it is used only for example.

P.P.P.S. And.. Please forgive my pure English :-)

-- 
Dmitry Morozhnikov
mailto:dmiceman at mail.ru