[ovs-discuss] mf_value and mf_subvalue size restrictions

Jesse Gross jesse at nicira.com
Sat Nov 8 04:13:05 UTC 2014


On Fri, Nov 7, 2014 at 3:12 PM, Madhu Challa <challa at noironetworks.com> wrote:
> I was referring to the bit mask present in the spec:
>
> A.2.3.5 Flow Match Field Masking
> When oxm_hasmask is 1, the OXM TLV contains a bitmask and its length
> is effectively doubled, so
> oxm_length is always even. The bitmask follows the field value and is
> encoded in the same way. The masks
> are defined such that a 0 in a given bit position indicates a “don’t
> care” match for the same bit in the
> corresponding field, whereas a 1 means match the bit exactly
>
> So if a mask is present with a Geneve option the max oxm_length could
> be 256 bytes which will not fit a single oxm ?

This may be a reason to find a different way to do the encoding of the
Geneve type. The payload of a single option maxes out at 124 bytes so
that will always fit in an OXM. However, eating away at that some for
the experimenter ID and option header would push us over the edge so
maybe that calls for the mapping table approach or some other way to
avoid having the header there.



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