linux-kernel - Re: [PATCH 00/12] Add kdbus implementation

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Message-ID: <alpine.LRH.2.00.1410300019570.11562@twin.jikos.cz>
Date:	Thu, 30 Oct 2014 00:24:02 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:	Jiri Kosina <jkosina@...e.cz>, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, john.stultz@...aro.org,
	arnd@...db.de, tj@...nel.org, marcel@...tmann.org, desrt@...rt.ca,
	hadess@...ess.net, dh.herrmann@...il.com, tixxdz@...ndz.org,
	simon.mcvittie@...labora.co.uk, daniel@...que.org,
	alban.crequy@...labora.co.uk, javier.martinez@...labora.co.uk,
	teg@...m.no
Subject: Re: [PATCH 00/12] Add kdbus implementation

On Wed, 29 Oct 2014, Greg Kroah-Hartman wrote:

> > > kdbus is a kernel-level IPC implementation that aims for resemblance to
> > > the the protocol layer with the existing userspace D-Bus daemon while
> > > enabling some features that couldn't be implemented before in userspace.
> > 
> > I'd be interested in the features that can't be implemented in userspace 
> > (and therefore would justify existence of kdbus in the kernel). Could you 
> > please point me to such list / documentation?
> 
> Lennart has given whole talks about this in the past, here's a recent
> talk going into the details:
> 	https://www.youtube.com/watch?v=HPbQzm_iz_k

I think it's a reasonable expectation that kernel patch submissions should 
be reasonably self-contained though. We've always been very strict about 
pushing everybody to provide extensive cover letters, changelogs and 
explanations, so this shouldn't really be an exception, I think.

> > It seems to me that most of the highlight features from the cover letter 
> > can be "easily" (for certain definition of that word, of course) 
> > implemented in userspace (vmsplice(), sending fd through unix socket, user 
> > namespaces, UUID management, etc).
> 
> We have dbus in userspace today, but that requires extra copies of data,

But we can do zero-copy between processess for quite some time already, so 
what exactly is the issue here?

> and isn't easy, or even possible, to do some of the application-specific
> bus logic that kdbus provides.  

I unfortunately have absolutely no idea what should I imagine here.

> See the talk above for details, there are slides around somewhere with 
> just text that we can add to the cover letter if that will help out in 
> future spins of this patch series.

I think that would be very helpful. Thanks.

-- 
Jiri Kosina
SUSE Labs

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