Date:	Wed, 9 Jul 2014 11:44:28 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	Daniel Borkmann <dborkman@...hat.com>, davem@...emloft.net,
	geirola@...il.com, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org
Subject: Re: [PATCH net-next 0/5] SCTP updates

On Wed, Jul 09, 2014 at 11:36:07AM -0400, Vlad Yasevich wrote:
> On 07/09/2014 11:13 AM, Neil Horman wrote:
> > On Wed, Jul 09, 2014 at 03:28:03PM +0200, Daniel Borkmann wrote:
> >> On 07/09/2014 12:49 PM, Neil Horman wrote:
> >>> On Wed, Jul 09, 2014 at 11:57:37AM +0200, Daniel Borkmann wrote:
> >>>> On 07/08/2014 04:41 PM, Neil Horman wrote:
> >>>>> On Tue, Jul 08, 2014 at 04:05:26PM +0200, Daniel Borkmann wrote:
> >>>>>> On 07/08/2014 01:14 PM, Neil Horman wrote:
> >>>>>> ...
> >>>>>>> since you're adding cmsg's from rfc6458, do you also want to add some
> >>>>>>> deprecation warnings around the use of SCTP_SNDRCVINFO too, so we can start to
> >>>>>>> schedule its eventual removal?
> >>>>>>
> >>>>>> Sure, we can do that. Do you want me to include it into the set?
> >>>>>
> >>>>> If you're plan is to implement 6458, then yes, I think that would be good.
> >>>>
> >>>> Looking a bit closer at it, all our pr_warn_ratelimited(DEPRECATED ...)
> >>>> warnings in SCTP are being done in 'slowpath' {set,get}sockopt(2) operations
> >>>> only, which is fine. What you're suggesting is to place similar ratelimited
> >>>> warnings (due to different possible pids on the machine) into the 'fastpath'
> >>>> where we get and set cmsg message headers.
> >>>>
> >>>> While that may be fine for {set,get}sockopt(2) that's called once or very few
> >>>> times, I'm not sure this is a good idea in SCTP_SNDRCVINFO as it will yield
> >>>> to unnecessary spamming the klog since up to now this is the only way our
> >>>> users can set or receive this info. I'm not sure we want to annoy users like
> >>>> that ...
> >>>>
> >>> Then we wrap it in a ONCE macro so that it only triggers on the first use
> >>> instance.
> >>
> >> I'm not convinced about this so far. The whole point is that we also provide the
> >> pid just as we currently do, so that we give the user a chance to possibly pin
> >> point the process that needs code change to not use the deprecated API anymore.
> >>
> >>>> In how many years do you plan a removal ... I think we're stuck with uapi
> >>>> basically forever as we don't want to break old binaries, no? ;/
> >>>>
> >>> I thought we could remove things on a schedule if we followed the deprecation
> >>> process, but that may just be for sysfs.  Regardless, it would still be nice to
> >>> inform people they are using an older api.
> >>
> >> I think we rather might be stuck with also the deprecated stuff forever, just
> >> as AF_PACKET still has to carry around the old spkt stuff. :( So if we don't
> >> remove anything, there's actually also no point to spam the log about it, if
> >> everyone can/should read it from the RFC anyway.
> >>
> > So this begs the question as to why we have deprecation warnings to begin with.
> > At what point do we draw the line where we can change some aspect of the user
> > api.  I agree if the answer is never, then yeah we're stuck, but then, why
> > bother announcing deprecation warnings at all?
> 
> I think we can deprecate user API after a significantly long period of time
> (like 5 or 6 years).  That's why we also have a deprecation schedule that can
> be updated and hopefully that's something people pay attention to.
> 
> The problem here is deprecation of ancillary data and that's is a lot tougher
> then socket options.  In this particular case (SCTP_SNDRCVINFO vs SCTP_RCVINFO),
> I don't think there is any way to deprecate the SCTP_SNDRCVINFO since the event
> enabling it is the same as the one for SCTP_RCVINFO.  This was a mistake in the
> spec.  Ancillary data should not have been enabled using even notification api,
> as it is not an event, but we now have to live with it.
> 
Ugh I didn't even consider cmsg type overlap.  Thats probably it then, we can't
deprecate it.  Though that does call the question up as to how to differentiate
expectations of the data format for each cmsg, if they use the same type.  Does
the SCTP_RCVINFO data struct overlay the SNDRCVINFO struct exactly?  (sorry I've
not checked myself yet).

Neil

> -vlad
> 
> > 
> > Neil
> > 
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