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

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Message-Id: <7A6C94DE-C3B0-49FB-AE49-3E6706B675F0@lurchi.franken.de>
Date:	Wed, 18 Jun 2014 15:24:00 +0200
From:	Michael Tuexen <Michael.Tuexen@...chi.franken.de>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Vlad Yasevich <vyasevich@...il.com>,
	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 18 Jun 2014, at 15:16, David Laight <David.Laight@...LAB.COM> 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.
Well, you can have an additional field in the struct to do that...
I wouldn't say that it is forbidden...
> 
> What does FreeBSD do about the 'sockaddr_storage'?
Need to double check, but we just use it as an large enough memory
block to hold struct sockaddr_in and struct sockaddr_in6. There was
a lengthy discussion a long time ago and that was the compromise...
> 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.
Would't you use struct sockaddr * for that?

Best regards
Michael
> 
> 	David
> 
> 
> 
> 
> 

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