Compatibility between D-Bus and kdbus

Lennart Poettering mzqohf at
Wed Nov 26 02:51:57 PST 2014

On Tue, 25.11.14 18:52, Thiago Macieira (thiago at wrote:

> 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.

Well, i figure qtdbus has a way to install completely generic matches?
Like for example a simple match being the precise string
"arg0=''"? If so, then this might result in two matches being
installed. Firstly, a bloom filter match for the field in
question. And secondly a match against NameOwnerChanged messages from
the kernel, without bloom filter, since a match a generic as the one
mentioned could also match against NameOwnerChanged messages.


Lennart Poettering, Red Hat

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