Date:	Wed, 09 Jul 2014 12:32:55 -0400
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Neil Horman <nhorman@...driver.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 07/09/2014 11:44 AM, Neil Horman wrote:
> 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).

No there is not direct overlap between the two.  However, as Michael pointed out,
there is a new option to control SCTP_RCVINFO.  So would could add a deprecation
warning to the over SCTP_EVENTS option and carry SCTP_SNDRCVINFO with it.
Once SCTP_EVENTS goes away so can SCTP_SNDRCVINFO.

-vlad

> 
> Neil
> 
>> -vlad
>>
>>>
>>> Neil
>>>
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