netdev - Re: [PATCH net-next 0/6] A step closer to RFC 6458 compliancy

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Message-ID: <53A19339.80908@gmail.com>
Date:	Wed, 18 Jun 2014 09:25:13 -0400
From:	Vlad Yasevich <vyasevich@...il.com>
To:	David Laight <David.Laight@...LAB.COM>,
	'Michael Tuexen' <Michael.Tuexen@...chi.franken.de>
CC:	Geir Ola Vaagland <geirola@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>
Subject: Re: [PATCH net-next 0/6] A step closer to RFC 6458 compliancy

On 06/18/2014 09:16 AM, David Laight wrote:
> From: Michael Tuexen [ 
>> On 18 Jun 2014, at 10:42, David Laight <David.Laight@...LAB.COM> wrote:
>>
>>> From: Vlad Yasevich
>>>> On 06/17/2014 11:36 AM, David Laight wrote:
>>>>> From: Of Geir Ola Vaagland
>>>>>> These patches are part of my master thesis project. I have been searching for discrepancies
>> between
>>>>>> the socket API specificiation in RFC 6458 and the current Linux SCTP implementation. The
>> following
>>>>>> patches are my humble attempts at getting somewhat closer to compliancy.
>>>>>
>>>>> I've just been reading RFC 6458 - HTF did it get past the editors and
>>>>> then published in its current form?
>>>>> Lots of the structures have implied padding.
>>> ...
>>>> I've argued the padding issue, but the editor stance is that it's implementation
>>>> dependent.
>>>
>>> It wouldn't be as bad if the RFC said that the structure contained the
>>> fields that followed (as is typical of the posix definitions),
>>> but instead it gives a definition of the structure.
> 
>> That would have been a possibility, but it was never suggested.
>> As far as I know, C does not guarantee the memory layout for structs,
>> except for the sequence of the components. So a compiler might add
>> some padding at any place. When implementing this, you need to take
>> care of this (and your job might be simpler, since you might only
>> work with a specific set of compilers).
>> In FreeBSD we also added some padding to some structures since they
>> "evolved" during the lifetime of of the internet draft and we wanted
>> to preserve some compatibility.
>> I agree, that one must take care of the implied padding and I will double
>> check how this is handled in FreeBSD. Not sure...
> 
> You need to add explicit named pad fields in order to zero them.
> (since you don't really want a memset())
> That is against my reading of the RFC.
> 
> What does FreeBSD do about the 'sockaddr_storage'?
> I'd have thought it had the same rules as NetBSD - where (IIRC) it should never
> be instantiated, but only exists as a pointer type for function parameters.
> 

I don't remember any such rules when sockaddr_storage was defined.  Can you
point to any document stating such rules?
It is definitely useful as a container object at times.

-vlad

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