[ovs-dev] [PATCH 3/8] nx-match: Do not check pre-requisites for load actions

Simon Horman horms at verge.net.au
Tue Oct 30 00:59:25 UTC 2012

On Mon, Oct 29, 2012 at 09:58:58AM -0700, Ben Pfaff wrote:
> On Sat, Oct 27, 2012 at 03:05:57PM +0900, Simon Horman wrote:
> > There are (or at least will be) cases where this check can produce false
> > positives.  For example, a flow which matches a non-MPLS packet and then
> > applies an MPLS push action followed by an action to load the MPLS label.
> So, I remember the discussion, but I don't remember coming to exactly
> this conclusion.
> The problem seems to be, at this point, MPLS specific, because for
> most prerequisites, whether it is satisfied cannot be affected by
> actions.  For example, no action can transform a TCP packet into a
> non-TCP packet, and vice versa.
> My thought is, then, for now we should define a new function to test
> whether a prerequisite could ever be satisfied given a particular
> flow.  For all prerequisites other than MPLS, this would return the
> same thing as mf_are_prereqs_ok(); for MPLS, it could just return
> true.

I think that I am comfortable with that approach, I will implement it
and see how things go.

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