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

Ben Pfaff blp at nicira.com
Mon Oct 29 16:58:58 UTC 2012


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.



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