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

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Date:	Thu, 30 Apr 2015 12:19:00 +0200
From:	Łukasz Stelmach <l.stelmach@...sung.com>
To:	Richard Weinberger <richard@....at>
Cc:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Theodore Ts'o <tytso@....edu>,
	Harald Hoyer <harald@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] kdbus for 4.1-rc1

It was <2015-04-30 czw 11:12>, when Richard Weinberger wrote:
> Am 30.04.2015 um 11:05 schrieb Łukasz Stelmach:
>> Regardless, of initrd issues I feel there is a need of a local IPC
>> that is more capable than UDS. Linus Torvalds is probably right that
>> dbus-daemon is everything but effictient. I disagree, however, that
>> it can be optimised and therefore solve *all* issues kdbus is trying
>> to address. dbus-deamon, by design, can't some things. It can't
>> transmitt large payloads without copying them. It can't be made
>> race-free.
>
> This is true.
> But as long dbus-deamon is not optimized as much as possible there is
> no reason to force push kdbus.
> As soon dbus-deamon exploits all kernel interfaces as much it can and
> it still needs work (may it performance or other stuff) we can think
> of new kernel features which can help dbus-deamon.

I may not be well informed about kernel interfaces, but there are some
use cases no dbus-daemon optimisation can make work properly because of
rece-conditons introduced by the user-space based message router.

For example, a service can't aquire credentials of a client process that
actually sent a request (it can, but it can't trust them). The service
can't be protected by LSM on a bus that is driven by dbus-daemon. Yes,
dbus-daemon, can check client's and srevice's labels and enforce a
policy but it is going to be the daemon and not the LSM code in the
kernel.

-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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