Since OVS keeps desired state in a DB, upon sudden crash of the
host we may leave a port behind. There's no problem on VM
shutdown or NIC hotunplug as we call corresponding del-port
function (virNetDevOpenvswitchRemovePort()). But if the host
suddenly crashes we won't ever do that. What happens next, is
when OVS starts it finds desired state in its DB and creates a
stale port.

OVS added support for transient ports in v2.5.0 (Feb 2016) and
since its v2.9.0 it even installs a systemd service
(ovs-delete-transient-ports) that automatically deletes transient
ports on system startup. If we mark a port as transient then OVS
won't restore its state on restart after crash.

This change may render "--may-exist" argument redundant, but I'm
not sure about all the implications if it was removed. Let's keep
it for now.

Resolves: https://gitlab.com/libvirt/libvirt/-/issues/615
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 src/util/virnetdevopenvswitch.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/util/virnetdevopenvswitch.c b/src/util/virnetdevopenvswitch.c
index f1765ae1c8..e23f4c83b6 100644
--- a/src/util/virnetdevopenvswitch.c
+++ b/src/util/virnetdevopenvswitch.c
@@ -164,7 +164,9 @@ int virNetDevOpenvswitchAddPort(const char *brname, const char *ifname,
 
     cmd = virNetDevOpenvswitchCreateCmd(&errbuf);
     virCommandAddArgList(cmd, "--", "--may-exist",
-                         "add-port", brname, ifname, NULL);
+                         "add-port", brname, ifname,
+                         "--", "set", "Port", ifname, "other_config:transient=true",
+                         NULL);
 
     virNetDevOpenvswitchConstructVlans(cmd, virtVlan);
 
-- 
2.43.2
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On 4/22/24 3:56 AM, Michal Privoznik wrote:
> Since OVS keeps desired state in a DB, upon sudden crash of the
> host we may leave a port behind. There's no problem on VM
> shutdown or NIC hotunplug as we call corresponding del-port
> function (virNetDevOpenvswitchRemovePort()). But if the host
> suddenly crashes we won't ever do that. What happens next, is
> when OVS starts it finds desired state in its DB and creates a
> stale port.
> 
> OVS added support for transient ports in v2.5.0 (Feb 2016) and
> since its v2.9.0 it even installs a systemd service
> (ovs-delete-transient-ports) that automatically deletes transient
> ports on system startup. If we mark a port as transient then OVS
> won't restore its state on restart after crash.
> 
> This change may render "--may-exist" argument redundant, but I'm
> not sure about all the implications if it was removed. Let's keep
> it for now.
> 
> Resolves: https://gitlab.com/libvirt/libvirt/-/issues/615
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> ---
>   src/util/virnetdevopenvswitch.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/src/util/virnetdevopenvswitch.c b/src/util/virnetdevopenvswitch.c
> index f1765ae1c8..e23f4c83b6 100644
> --- a/src/util/virnetdevopenvswitch.c
> +++ b/src/util/virnetdevopenvswitch.c
> @@ -164,7 +164,9 @@ int virNetDevOpenvswitchAddPort(const char *brname, const char *ifname,
>   
>       cmd = virNetDevOpenvswitchCreateCmd(&errbuf);
>       virCommandAddArgList(cmd, "--", "--may-exist",
> -                         "add-port", brname, ifname, NULL);
> +                         "add-port", brname, ifname,
> +                         "--", "set", "Port", ifname, "other_config:transient=true",
> +                         NULL);
>   
>       virNetDevOpenvswitchConstructVlans(cmd, virtVlan);
>   

While checking this out, I noticed that the machine I was testing on 
still has ports on its OVS bridge that I had manually created back in 
2021 the last time I touched anything related to OVS :-). After adding a 
new port using the modified commandline, I rebooted the machine and the 
pre-existing "stale" interfaces were still there, but the one I had just 
created with transient=true was gone.

Reviewed-by: Laine Stump <laine@redhat.com>
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