netdev - Re: [RFC net-next 1/1] : sctp: denoise deprecation log on SCTP

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Date:	Thu, 9 Jul 2015 09:59:47 -0300
From:	Marcelo Ricardo Leitner <mleitner@...hat.com>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	Jamal Hadi Salim <jhs@...atatu.com>,
	Neil Horman <nhorman@...driver.com>,
	Vlad Yasevich <vyasevic@...hat.com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	tuexen@...muenster.de
Subject: Re: [RFC net-next 1/1] : sctp: denoise deprecation log on SCTP_EVENTS

On Thu, Jul 09, 2015 at 01:54:37PM +0200, Daniel Borkmann wrote:
> On 07/09/2015 12:38 PM, Jamal Hadi Salim wrote:
> ...
> >In the newer kernels this message is extremely noisy. After a quick
> >discussion with Daniel it seems to me it will be very hard to get
> >existing apps that nobody is going to update to continue to work
> >(i.e no forward compat). And newer apps that desire to play in both
> >older kernels and new kernels will have to play some tricks to work
> >(i.e weak backward compatibility).  These are good reasons
> >to totally get rid of this message. At minimal to neutre it.
> 
> To put some more context into this, here was the past discussion
> on this topic:
> 
>   http://www.spinics.net/lists/linux-sctp/msg03596.html
> 
> This begs the question, which we need to clarify:
> 
>   Can we *ever* get rid of the old UAPI that the RFC proposed
>   and later on deprecated?
> 
> In the thread, there was a mentioning of 5-6 years schedule, but
> I honestly doubt that this would be enough, i.e. for people only
> upgrading their kernels, but not being able to touch their legacy
> SCTP apps (maybe due to proprietary appliance crap, etc).
> 
> A pr_warn_once() would only warn for the first app triggering this
> (and not for follow-ups), it would surely take incentives away to
> update their code since less annoying, but if the uapi in fact
> could never be removed, then why bothering spamming the klog in
> the first place? ;) I can understand the deprecation dilemma, but
> personally, I would have no problem if we just want to remove the
> pr_warn_ratelimited() altogether ...
> 
> >The attached change tries to do that. However, if you had multiple
> >apps, you will only get warning for the first one.
> >
> >Will send proper patch when theres some consensus.

The new message is misleading as currently we don't have SCTP_EVENT 
available to use. So if someone tries to actually follow that lead, it
will lead to a dead and confusing end.

I'm okay with just switching it to pr_warn_once, though. It makes sense
to not spam klog but to have the message there, because even if we keep
it available for backwards compatibility, it might suffer from some
limitations in the future and the usage of the new one is always
recommended.

  Marcelo

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