On Mon, Jun 07, 2021 at 05:07:17PM -0400, Laine Stump wrote: > Connecting a tap device to an Open vSwitch is done by adding a "port" > to the switch with the ovs-vsctl "add-port" command. The port will > have the same name as the tap device, but it is a separate entity, and > can survive beyond the destruction of the tap device (although under > normal circumstances the port will be deleted around the same time the > tap device is deleted). > > This makes it possible for a port of a particular name to already > exist at the time libvirt calls ovs-vsctl to add that port. The > original commit of Open vSwitch support (commit df81004632, libvirt > 0.9.10, Feb. 2012) used the "--may-exist" option to the add-port > command to indicate that a port of the desired name might already > exist, and that it was okay to simply re-use this port (rather than > failing with an error message). > > Then in commit 33445ce8446d9 (libvirt 1.2.7, April 2014) the command > was changed to use "--if-exists del-port blah" instead of > "--may-exist". The reason given was that there was a bug in OVS where > a stale port would be unusable even though it still existed; the > workaround was to forcibly delete any existing port prior to adding > the new port (of the same name). This is the ovs-vsctl command still > in use by libvirt today. > > It recently came up in the discussion of a bug concerning guest packet > loss during OpenStack upgrades (https://bugzilla.redhat.com/1963164) > that the bug in OVS that necessitated the del-port workaround was > fixed quite a long time ago (August 2015): > > https://github.com/openvswitch/ovs/commit/e21c6643a02c6b446d2fbdfde366ea303b4c2730 > > thus rendering the workaround in libvirt unnecessary. The assertion in > that discussion is that this workaround is now the cause of the packet > loss being experienced during OpenStack upgrades. I'm not convinced > this is the case, but it does appear that there is no reason to carry > this workaround in libvirt any longer, so this patch reverts the code > back to the original behavior (using "--may-exist" instead of > "--if-exists del-port"). > > Signed-off-by: Laine Stump <laine@xxxxxxxxxx> Reviewed-by: Daniel P. Berrangé <berrange@xxxxxxxxxx> Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
