On Sat, Feb 18, 2012 at 10:07:45PM -0500, Laine Stump wrote:
> On 02/17/2012 02:51 PM, Ansis Atteka wrote:
> > On Fri, Feb 17, 2012 at 10:55 AM, Laine Stump <laine laine org
> > <mailto:laine laine org
> > On 02/16/2012 06:49 PM, Ansis Atteka wrote:
> > > Currently libvirt sets the attached-mac to altered MAC address
> > that has
> > > first byte set to FE. This patch will change that behavior by
> > using the
> > > original (unaltered) MAC address from the domain XML
> > configuration file.
> > Maybe I didn't read thoroughly enough, but I don't see where it
> > changes
> > the behavior - in the cases where previously the first byte was set to
> > 0xFE, now you send discourage=true, and in the cases where it didn't,
> > now you send discourage=false.
> > "discourage" means whether bridge should be discouraged to use the
> > newly added
> > TAP device's MAC address. Libvirt does that by setting the first MAC
> > address byte
> > high enough.
> > And here is how this patch works:
> > 1. Now in virNetDevTapCreateInBridgePort() function we always pass
> > exactly the same MAC address that was defined in XML.
> > 2. If "discourage" flag was set to true, then we create a copy of MAC
> > address and set its first byte to 0xFE
> > 3. virNetDevSetMAC() function would use the MAC address that was
> > product of #2
> > 4. while virNetDevOpenvswitchAddPort() function would use the
> > original MAC address that was passed in #1 (this code did not need
> > to be changed so most likely that was the reason why you did not
> > notice behavior changes)
> Right. That's what I missed - all I saw was every occurrence of creating
> a temporary mac address with 0xFE in the first byte replaced with adding
> "discourage=true" to the args. I didn't notice that
> virNetDevOpenvswitchAddPort() takes the macaddr (while
> virNetDevBridgeAddPort() doesn't).
> But that means that the tap device has been created with an
> 0xFE-initiated MAC address, and then you attach to the bridge using the
> unmodified address. Is the issue that the mac address used during the
> attach needs to match the MAC address that will be in the traffic? Do
> connections to an openvswitch bridge have an implied MAC filter on them,
> such that only that MAC address gets through?
> (Also, the only time discourage is false is for libvirt's virtual
> network bridges. I'm wondering if they could also use the modified MAC
> address for the tap devices - if that was the case we could just always
> create the temporary MAC address in virNetDevTapCreateInBridgePort()
> (and always set the tap device's mac to that).)
> Let's let this sit over the weekend and see if anyone else has a
> brilliant idea/insight.