linux-kernel - Re: kdbus: to merge or not to merge?

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Date:	Thu, 6 Aug 2015 20:14:27 +0200
From:	Daniel Mack <daniel@...que.org>
To:	Andy Lutomirski <luto@...capital.net>,
	David Herrmann <dh.herrmann@...il.com>
Cc:	Tom Gundersen <teg@...m.no>,
	"Kalle A. Sandstrom" <ksandstr@....fi>,
	Greg KH <gregkh@...uxfoundation.org>,
	Borislav Petkov <bp@...en8.de>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Havoc Pennington <havoc.pennington@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>, cee1 <fykcee1@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: kdbus: to merge or not to merge?

On 08/06/2015 05:21 PM, Andy Lutomirski wrote:
> Maybe gdbus really does use kdbus already, but on
> very brief inspection it looked like it didn't at least on my test VM.

No, it's not in any released version yet. The patches for that are being
worked on though and look promising.

> If the client buffers on !EPOLLOUT and has a monster buffer, then
> that's the client's problem.
> 
> If every single program has a monster buffer, then it's everyone's
> problem, and the size of the problem gets multiplied by the number of
> programs.

The size of the memory pool of a bus client is chosen by the client
itself individually during the HELLO call. It's pretty much the same as
if the client allocated the buffer itself, except that the kernel does
it on their behalf.

Also note that kdbus features a peer-to-peer based quota accounting
logic, so a single bus connection can not DOS another one by filling its
buffer.


Thanks,
Daniel
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