On Wed, Sep 12, 2012 at 12:09:41PM -0700, Ben Pfaff wrote: > On Wed, Sep 12, 2012 at 05:44:32PM +0900, Simon Horman wrote: > > By passing a flow to the action parser the pre-requisites > > of set-feild actions will be checked. If the flow is NULL, > > for instance in test code such as ofctl_parse_ofp11_instructions(), > > then the check is skiped, as it always was before this change. > > > > Unfortunately I don't think that this check is correct as > > it does not take into account other actions actions that may > > be applied before the load action, e.g. vlan push/pop, which may > > affect the pre-requisites. > > > > I believe that in its current form there is scope for both false positives > > (not so bad, perhaps) and false negatives (pretty bad). I would welcome > > some input on if these concerns are valid and if so how they may be > > overcome. > > When I've thought about this problem before, I wasn't able to come up > with an example of when the prerequisite check would be wrong. Do you > have an example?
I would very much like for this not to be a problem. But here are examples that I am concerned about. # MPLS false negative 1. Packet with no MPLS header arrives 2. Push MPLS action is applied 3. Set-Field:MPLS_LABEL action is applied The pre-requisite for 3 is Eth Type 0x8847 or 0x8848, but that isn't true until 2 is applied. # MPLS false positive 1. Packet with single MPLS header arrives 2. Pop MPLS action is applied 3. Set-Field:MPLS_LABEL action is applied The pre-requisite for 3 is Eth Type 0x8847 or 0x8848, which is true at 1 but not after 2 is applied. # VLAN false positive 1. Ppacket without VLAN header arrives 2. Push VLAN action is applied 3. Set-Field:VLAN_PCP is applied The pre-requisite for 3 is that VLAN_VID!=NONE, but this isn't true until 2 is applied. # VLAN false negative 1. Packet with single VLAN header arrives 2. Pop VLAN action is applied 3. Set-Field:VLAN_PCP is applied The pre-requisite for 3 is that VLAN_VID!=NONE, which is true at 1, but not after 2 is applied. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
