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List:       openvswitch-discuss
Subject:    [ovs-discuss] Concept of facets and subfacets
From:       xiaoma80.dev () gmail ! com (JieYue Ma)
Date:       2012-11-29 12:26:37
Message-ID: CAJ6iH_jYW--8pHQOQtmkM7PRSHTvRFAj-0_ffsTDT+tegKHS3A () mail ! gmail ! com
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As I understand, there are two kinds of flow in OVS. One is in the
user space, e.g. vswitchd, where flow key can include some wildcards
to match, while the other lies in kernel space, e.g. openvswitch.ko,
where the flow key can never have wildcard.

If no wildcard in user space flow (a.k.a facet), the flow from kernel
space (a.k.a subfacet) will exactly match its facet, which means one
facet has only one subfacet

If not, the user space flow can match multiple flows from kernel
space, leads to the scenario that one facet contains multiple
subfacets


I am not sure if I AM RIGHT, please point out if I am wrong, thanks

On Wed, Nov 28, 2012 at 1:34 PM, Ahmed Talha Khan <auny87 at gmail.com> wrote:
>
> Hey,
>
> While going through the code for OVS data path I could not really understand
> the need and functionality of facets and sub-facets. The code comment on
> "struct facet" explain it like this.
>
> From file "ofproto-dpif.c"
>
> "A facet associates a "struct flow", which represents the Open vSwitch
> userspace idea of an exact-match flow, with one or more subfacets.  Each
> subfacet tracks the datapath's idea of the exact-match flow equivalent to
> the facet.  When the kernel module (or other dpif implementation) and Open
> vSwitch userspace agree on the definition of a flow key, there is exactly
> one subfacet per facet.  If the dpif implementation supports more-specific
> flow matching than userspace, however, a facet can have more than one
> subfacet, each of which corresponds to some distinction in flow that
> userspace simply doesn't understand"
>
> "Each subfacet tracks the datapath's idea of the exact-match flow equivalent
> to the facet" ?? What does this means? The comments after this are obviously
> based on this line which i dont really understand. Can anybody explain what
> Facets are and what they imply ?
>
> --
> Regards,
> -Ahmed Talha Khan
>
>
> _______________________________________________
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> discuss at openvswitch.org
> http://openvswitch.org/mailman/listinfo/discuss
>

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