[ovs-dev] [PATCH] ofproto-dpif: Tighten up megaflow wildcard handling.

[Ben Pfaff]

On Wed, Jun 19, 2013 at 10:03:56AM -0700, Justin Pettit wrote:
> On Jun 19, 2013, at 9:21 AM, Ben Pfaff <blp at nicira.com> wrote:
> > I don't understand the change in compose_output_action__().  It adds
> > the ECN bits to the mask but I don't see anything there that depends
> > on those bits.
> > 
> > In do_xlate_actions(), why do OFPACT_SET_VLAN_VID and
> > OFPACT_SET_VLAN_PCP have new dependencies?  They do not read the
> > fields that they add to the mask.
> 
> In both of these cases, we're updating partial fields with a whole
> field "set", so I think the old value matters.

We need to generalize that principle.  The kernel sets large groups of
fields with a single action.  For example, there is a single action to
set the IPv4 source and destination address, TOS, TTL, IP protocol,
and fragment bits (*), so any action that sets any one of those needs to
add a dependency on the rest.

(*) The kernel won't allow actually changing the IP protocol or
    fragment bits.