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

Guru Shetty guru at ovn.org
Wed Nov 6 17:39:12 UTC 2019

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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