DBUS API questions

Havoc Pennington hp at redhat.com
Wed May 2 08:49:40 PDT 2007


>     I think I understand the difference between interfaces and object
> paths. I am still somewhat confused about how bus paths enter the
> picture. Some enlightenment would be appreciated.

Here is a good analogy:

bus name = hostname
unique bus name = IP address
interface = interface (in a language, like Java)
object path = object reference / pointer

The "hostname" analogy requires you to imagine that each process or 
application is a "host"

Don't try to overthink it. interface is just interface, bus name is the 
name of something on the bus (and the only things on the bus are 
processes), and object paths are names of objects. "Objects" has the 
same meaning you are used to, java.lang.Object, python object, GObject, etc.

I'll let others comment on the domain-specific stuff, but re: the API 
the DBus naming conventions would be like:


i.e. the method names are AllCaps not javaCaps. The interface names are 
also AllCaps (as in Java and many other things).

Also, on the struct interface you posted, I would not have getType(), 
getLength(), etc. as remote IPC calls. Remember, when remoting, round 
trips = bad. Using this object would involve too many little round trips.

Instead, have one method that returns all the info in one D-Bus struct, 
for example.

> I am assuming here that there is a native DBUS interface for getting a
> list of all objects under a specific path. (something like: ls
> /org/libsmbios/table/byHandle/*) In that case, iterOverType() may not be
> necessary.

This info can be in the results of Introspect() but it is not all that 
convenient an API for a typical app since it would involve parsing XML.
You might want to have a method that just returns an array of object paths.


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