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

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Date:	Wed, 18 Jun 2014 13:53:22 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Michael Tuexen' <Michael.Tuexen@...chi.franken.de>,
	Vlad Yasevich <vyasevich@...il.com>
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

From: Michael Tuexen 
> On 18 Jun 2014, at 15:25, Vlad Yasevich <vyasevich@...il.com> wrote:
> 
> > 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.
> I agree. The description would be OK for struct sockaddr. I have never instantiated
> a variable of that type. The only use (I know of) of struct sockaddr_storage
> is as a container object.

I remember Christos saying something to that effect on one of the NetBSD lists.
But I can't remember exactly when and searching the archives might be hard.
He might remember.

	David



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