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

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Date:	Fri, 3 Jul 2015 17:13:37 +0800
From:	cee1 <fykcee1@...il.com>
To:	Łukasz Stelmach <l.stelmach@...sung.com>
Cc:	Richard Weinberger <richard@....at>,
	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>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [GIT PULL] kdbus for 4.1-rc1

2015-04-30 22:52 GMT+08:00 Łukasz Stelmach <l.stelmach@...sung.com>:
> It was <2015-04-30 czw 14:45>, when Richard Weinberger wrote:
>> Am 30.04.2015 um 14:40 schrieb Łukasz Stelmach:
>>> It was <2015-04-30 czw 14:23>, when Richard Weinberger wrote:
>>>> Am 30.04.2015 um 14:16 schrieb Łukasz Stelmach:
>>>>> 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.
>>> [...]
>>>>>>> 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)?
>>>>
>>>> The question is whether it makes sense to collect this kind of meta data.
>>>> I really like Andy and Alan's idea improve AF_UNIX or revive AF_BUS.
>>>
>>> Race conditions have nothing to do with metadata. Neither has LSM
>>> support.
>>
>> Sorry, I thought you mean the races while collecting metadata in userspace...
>
> My bad, some reace conditions *are* associated with collecting metadata
> but ont all. It is impossible (correct me if I am wrong) to implement
> reliable die-on-idle with dbus-daemon.
>
>>> AF_UNIX with multicast support wouldn't be AF_UNIX anymore.
>>>
>>> AF_BUS? I haven't followed the discussion back then. Why do you think it
>>> is better than kdbus?
>>
>> Please see https://lwn.net/Articles/641278/
>
> Thanks. If I understand correctly, the author suggests using EBPF on a
> receiveing socket side for receiving multicast messages. This is nice if
> you care about introducing (or not) (too?) much of new code. However,
> AFAICT it may be more computationally complex than Bloom filters because
> you need to run EBPF on every receiving socket instead of getting a list
> of a few of them to copy data to. Of course for small number of
> receivers the "constant" cost of running the Bloom filter may be higher.

Still think about the idea of implementing KDBUS in the form of socket.

What about using __multicast group__ instead of EBPF, to send/receive
multicast message?

(Which can implement the bloom filter as follows ?) E.g.

Sender:
        send to multi_address

Receivers:
        if ((multi_address & joined_address) == joined_address) {
                /* a message for us */
        }

Then we can further apply EBFP to remove the "False positive" case,
which will otherwise wake up user space code, and let it clear "False
positive" case.



-- 
Regards,

- cee1
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