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

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Date:	Wed, 5 Aug 2015 09:10:50 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Havoc Pennington <havoc.pennington@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tom Gundersen <teg@...m.no>, Daniel Mack <daniel@...que.org>,
	"Kalle A. Sandstrom" <ksandstr@....fi>,
	Borislav Petkov <bp@...en8.de>, cee1 <fykcee1@...il.com>
Subject: Re: kdbus: to merge or not to merge?

Hi

On Tue, Aug 4, 2015 at 4:47 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Tue, Aug 4, 2015 at 7:09 AM, David Herrmann <dh.herrmann@...il.com> wrote:
>> This is a bug in the proxy (which is already fixed).
>
> Should I expect to see it in Rawhide soon?

Use this workaround until it does:

    $ DBUS_SYSTEM_BUS_ADDRESS="kernel:path=/sys/fs/kdbus/0-system/bus"
./your-binary

> Anyway, the broadcasts that I intended to exercise were
> KDBUS_ITEM_ID_REMOVE.  Those appear to be broadcast to everyone,
> irrespective of "policy", so long as the "match" thingy allows it.

Matches are opt-in, not opt-out. Nobody will get this message unless
they opt in.

> The bloom filter thing won't help at all according to the docs: bloom
> filters don't apply to kernel-generated notifications.

Bloom filters apply to message payloads. Kernel notifications do not
carry a message payload. Message metadata can be filtered for
explicitly (without false-positives).

> So yes, as far as I can tell, kdbus really does track object lifetime
> by broadcasting every single destruction event to every single
> receiver (subject to caveats above) and pokes the data into every
> receiver's tmpfs space.

Broadcast reception is opt-in.

Thanks
David
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