If I understand the question correctly, OVS handles this situation by
installing the new version of the flow using DPIF_FP_ZERO_STATS, which
causes the datapath flow's statistics to be zeroed and to report the
previous statistics to userspace.

On Sat, Jan 21, 2012 at 11:19:28AM +0530, Ramana Reddy wrote:
> When the first packet is coming to datapath, the datapath does not know
> what to do, and its handover to userspace, and userspace program will
> insert the necessary actions along with the flow in the kernel path.
> Later, all subsequent packets taken care of the fast path, and the
> respective stats are updated in the datapath.
> 
> Now, assume that the packets are redirected to another path some time, not
> the datapath. In this case, the datapath entry for that respected flow will
> be deleted, if the flow is not reaches to datapath with in the expiry time.
> But in my scenario, the flow definitely passes again the datapath with in
> the expiry time. In this case, the datapath stats are not valid and needs
> update from user space before the packet reaches to datapath again, so that
> the stats are valid thereafter.
> 
> Thanks,
> Ramana.
> 
> 
> 
> 
> On Fri, Jan 20, 2012 at 11:47 PM, Ben Pfaff <[email protected]> wrote:
> 
> > What is a non-expiry flow?
> >
> > I don't understand the sentence that begins "This is possible."
> >
> > On Fri, Jan 20, 2012 at 09:36:46PM +0530, Ramana Reddy wrote:
> > > Hi Ben,
> > > Thanks for your reply. As you mentioned the datapath updates
> > > its own stats. But I need to update the stats for a given non-expiry
> > flow in
> > > the datapath from user space.
> > >
> > > This is possible, if the flow is deviated from the datapath certain time
> > > (less than
> > > the expiry time).
> > >
> > > Thanks,
> > > Ramana.
> > >
> > >
> > > On Fri, Jan 20, 2012 at 9:06 PM, Ben Pfaff <[email protected]> wrote:
> > >
> > > > On Fri, Jan 20, 2012 at 06:19:30PM +0530, Ramana Reddy wrote:
> > > > > How to update the datapath stats from user space in OVS-1.2.2.
> > > > > Is facet_update_stats in ofproto-dpif.c does this.
> > > > > If not what is the API from user space which is updating the
> > > > > stats.
> > > >
> > > > I don't really know what you're asking.  A straightforward
> > > > interpretation is that the datapath updates its own stats.  But that is
> > > > probably not what you are asking.  Can you ask a more specific
> > question?
> > > >
> >
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