Compatibility between D-Bus and kdbus

Thiago Macieira thiago at
Tue Nov 25 18:52:15 PST 2014

On Wednesday 26 November 2014 00:59:05 Lennart Poettering wrote:
> > Another point we have to take into account is that we'll have fewer rules
> > now  because the syntax is simpler. The client library will need to sort
> > out false positives and drop unneeded messages. That said, the number
> > can't be too small.
> Actually the kdbus match logic should not allow fewer rules, and the
> syntax isn't any simpler. kdbus matches are as fine-grained as dbus1
> matches, though they are probabilistic and might allow false
> positives. In fact, since the bloom stuff cannot be used to match
> against kernel signals like NameOwnerChanged you might need *more*
> matches on kdbus than on dbus1...

I don't think QtDBus would need more. If as you say the new rule mechanism 
with bloom filters is as powerful as the old one, then we'll produce exactly as 
many rules.

QtDBus by itself does not listen to NameOwnerChanged without also specifying 
the first string argument. Those would translate to name notifications 1:1 

In the future, if the bloom filter mechanism is powerful enough, we may be able 
to create more precise rules and thus add two rules where today we have a 
single one. Given how precise QtDBus is today already, I expect that those 
situations will be few and far between.

Thiago Macieira - thiago (AT) - thiago (AT)
   Software Architect - Intel Open Source Technology Center
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