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

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Message-id: <87oam5olpu.fsf%l.stelmach@samsung.com>
Date:	Thu, 30 Apr 2015 14:16:13 +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 12:40>, when Richard Weinberger wrote:
> Am 30.04.2015 um 12:19 schrieb Łukasz Stelmach:
>> 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.
>
> That's why I said we can think of new kernel features if they are
> needed.  But they current sink or swim approach of kdbus folks is also
> not the solution.  As I said, if dbus-daemon utilizes the kernel
> interface as much as possible we can think of new features.

What kernel interfaces do you suggest to use to solve the issues
I mentioned in the second paragraph: race conditions, LSM support (for
example)?

BTW. Does anyone know how microkernel-based OSes implement sockets?
-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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