DBus in the kernel?

[Thiago Macieira]

Em Quarta-feira 06 Janeiro 2010, às 13:00:19, Ian Molton escreveu:
> Lennart Poettering wrote:
> > That is certainly doable, and is in fact done by some projects
> > (i.e. bluez passes BT audio via such a side-channel). However it kinda
> > sucks that as soon as you want to pass more than boring control data
> > you cannot use dbus anymore and need to invent your own protocol.
> 
> well, you either need to use data than dbus can marshall efficiently or
> not... OTOH, I'd have thought a byte stream could be marshalled with
> damn near zero overhead. (other than dbus' current two context switch
> overhead)

Not exactly.

First of all, it cannot be done without memcpy, which also means the library 
must allocate a chunk of memory that matches your byte array size.

Second, the way that it's written, the marshalling code is inefficient. There's 
some overhead here. Same thing for the dermashalling.

Third, the validation routines also add some overhead, and they're run on the 
sender side, on the bus (probably upon receipt then before sending) and again 
on the client side. The D-Bus message format requires sequential parsing.

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Senior Product Manager - Nokia, Qt Development Frameworks
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