linux-kernel - Re: [RFC PATCH] xfrm: fix handling of XFRM policies mark and mask.

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Date:	Thu, 7 Feb 2013 13:54:37 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Emmanuel Thierry <emmanuel.thierry@...ecom-bretagne.eu>
Cc:	jamal <j.hadi123@...il.com>, Romain KUNTZ <r.kuntz@...lavors.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	herbert@...dor.apana.org.au,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jamal Hadi Salim <hadi@...erus.ca>
Subject: Re: [RFC PATCH] xfrm: fix handling of XFRM policies mark and mask.

On Thu, Feb 07, 2013 at 12:08:22PM +0100, Emmanuel Thierry wrote:
> 
> This is a nice idea, however you keep the insertion asymmetric. The usage of xfrm marks in non-conflicting cases will be made possible, but it stays disturbing for a user as the initial example will still have the same behavior:
> * Inserting the marked one then the unmarked will succeed
> * Inserting the unmarked then the marked one will fail
> This gives to the user the feeling of an indeterministic behavior of the xfrm module.

This was intended. Inserting the marked one then the unmarked
is a working scenario. Some users might rely on it, so we can't
change this as you proposed.

On the other hand, inserting the unmarked one then the marked
might result in a wrong policy lookup, so we can't allow this.
The only possibility we have, is inserting with different
priorites and that's what I'm proposing.

I fear we have to live with that asymmetric behaviour if
both policies have the same priority.

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