linux-kernel - Re: [GIT PULL] kdbus for 4.1-rc1

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Date:	Wed, 15 Apr 2015 21:41:36 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Havoc Pennington <hp@...ox.com>, Rik van Riel <riel@...hat.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tom Gundersen <teg@...m.no>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>
Subject: Re: [GIT PULL] kdbus for 4.1-rc1

On Wed, Apr 15, 2015 at 01:22:12PM -0700, Andy Lutomirski wrote:

> This leads me to a potentially interesting question: where's the
> buffering?  If there's a bus with lots of untrusted clients and one of
> them broadcasts data faster than all receivers can process it, where
> does it go?
> 
> At least with a userspace solution, it's clear what the OOM killer
> should kill when this happens.  Unless it's PID 1.  Sigh.

... and there is a PID 1 specimen that really likes to spew over dbus.
A lot.  I had never been able to find out _why_ does systemd feel like
broadcasting all kinds of stuff from PID 1 - maybe somebody in this
thread can answer that.  For example, what's the point of broadcasting
mount table updates, when
	* it can't hope to catch all individual changes - they _can_ get
lumped together, no matter what it tries.
	* any process can just as easily keep track of that data on its
own as it could by watching those broadcasts; parsing /proc/self/mountinfo
isn't harder than parsing notifications.
	* you need to start with obtaining the original state somehow, or
what would you apply those updates to?
	* if one insists on having a daemon doing such broadcasts, what
the hell is the point of having PID 1 do that?  Exact same logics would
do just fine.  Moreover, you could have one running in a namespace of
your session, which is something PID 1 won't see.

Sure, I understand why it wants to be aware of what's mounted and where it's
mounted.  Just as it wants to know what time it is.  Should it broadcast
a dbus message every second, just to tell everyone what had it found about
the time?

I'm somewhat tempted to propose AF_TWITTER - would match the style... ;-/
And frankly, this really looks like a social media braindamage - complete
with status update broadcast every time a plane flies by...
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