[ovs-discuss] OVS deleting flows from the datapath on exit

[Ben Pfaff]

I posted a series to change this behavior:
https://mail.openvswitch.org/pipermail/ovs-dev/2019-November/364812.html
https://mail.openvswitch.org/pipermail/ovs-dev/2019-November/364811.html

On Wed, Nov 06, 2019 at 10:13:16AM -0800, Ben Pfaff wrote:
> You might be right.
> 
> I don't think this affects what actions we shoudl take, though.  It
> still seems better to use "exit" to stop OVS gracefully.
> 
> I'm working on a patch to make "exit" avoid removing flows unless
> --cleanup is passed in.  It's slow going because I've got higher
> priorities things to do.
> 
> On Wed, Nov 06, 2019 at 09:39:12AM -0800, Guru Shetty wrote:
> > It may have come from this commit instead:
> > 
> > commit 9b5422a98f817b9f2a1f8224cab7e1a8d0bbba1f
> > Author: Ilya Maximets <i.maximets at samsung.com>
> > Date:   Wed Dec 16 15:32:21 2015 +0300
> > 
> >     ovs-lib: Try to call exit before killing.
> > 
> >     While killing OVS may not free all allocated resources.
> > 
> > Previously we used to SIGTERM ovs-vswitchd and even now, it looks like
> > doing that prevents the flush of datapath flows.
> > 
> > On Fri, 1 Nov 2019 at 13:35, Ben Pfaff <blp at ovn.org> wrote:
> > 
> > > OVS currently can gracefully exit in two ways: either with or without
> > > deleting the datapath.  But, either way, it deletes all of the flows
> > > from the datapath before it exits.  That is due to commit e96a5c24e853
> > > ("upcall: Remove datapath flows when setting n-threads."), which was
> > > first released in OVS 2.1 back in 2014.
> > >
> > > This isn't usually a big deal.  However, some controller folks I'm
> > > talking to are concerned about upgrade.  If the datapath flows persisted
> > > after OVS exits, then existing network connections (and perhaps some
> > > that are "similar" to them because they match the same megaflows) could
> > > carry on while the upgrade was in progress.
> > >
> > > I am surprised that I have not heard complaints about this in the 5
> > > years that the behavior has been this way.  Does anyone have any stories
> > > to report about it now that I bring it up?  Contrariwise, if we changed
> > > OVS so that it did not delete datapath flows on exit, can anyone suggest
> > > what problems that might cause?
> > >
> > > Thanks,
> > >
> > > Ben.
> > > _______________________________________________
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> > >