Hello,

My name is Kevin Tower and I am a systems engineer and self-proclaimed
virtualization evangelist at the University of Washington.  We make use of
the downstream fork of XCP -- XenSever, but I use XCP in some of my
personal dev environments.  We have been attempting to make use of the
"port locking" functionality that was added in 6.1 / 1.6, but I believe it
to be broken.  Details of the issue follow, as well as a proposed fix.

I see that George Shuklin made a commit to the code 3 months ago (see
https://github.com/xen-org/xen-api/commit/06c2d0fedc7031c27ad9215a751c404fde1ebb70
)
that made changes to the script regarding this feature, but my tests have
shown that this change is insufficient to handle all use cases.

When attempting to use the port-locking features on a VIF that is connected
to a "normal" network (no VLAN tags), the logic works correctly.  However,
It breaks when a VLAN-tagged network comes into play.  What happens is that
the VLAN network is added to the network as a "fake bridge," to use the
vSwitch terminology, which is a child object to the primary bridge device.
 When a VIF is attached to the (VLAN-tagged) network, it is associated with
this fake bridge instead of the real bridge.  So, when this script is
called against such a VIF, the get_bridge_name_vswitch() function returns
the name of the fake bridge instead of the real one.

The problem is that most of the ovs-* Open vSwitch utilities, including the
ovs-ofctl that is used to set up the VIF filters, don't recognize the fake
bridge as a valid bridge device and fail, and the port locking rules never
get added.  Also, the way this script is written, these failures are silent
because the return code is not captured, but I have not done anything about
that.

I have tested a fix that appears to work in both the VLAN and the non-VLAN
case.  Roughly described, after getting a bridge device name by executing
"ovs-vsctl iface-to-br vif_name", I run  "ovs-vsctl br-to-parent
bridge_device" and return that instead.  If the bridge device is a fake
bridge, it returns the "real" bridge device name, but if it is already a
real bridge device, it returns the same device name that was passed as a
parameter.

I am somewhat unfamiliar with the process for contributing bug fixes to an
open source project (if this fix is accepted, it will be my first!), and I
am also pretty new to git (I've used other source control systems, though).
 What is the best way for me to provide my suggested fix?  Should I post
the .diff here on the mailing list?  Should I create a pull request from my
own fork of the xen-api repository on github that has the suggested code
changes?

Thanks in advance,

Kevin Tower
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