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Re: [libvirt] [PATCH 0/4] Support mac and port profile for <interface type='hostdev'>

On 03/02/2012 03:03 PM, Roopa Prabhu wrote:
> On 3/2/12 11:04 AM, "Laine Stump" <laine laine org> wrote:
>> On 03/01/2012 04:02 AM, Roopa Prabhu wrote:
>>> This patch series is based on laines patches to support <interface
>>> type='hostdev'>.
>>> https://www.redhat.com/archives/libvir-list/2012-February/msg01126.html
>>> It support to set mac and port profile on an interface of type hostdev.
>>> * If virtualport is specified, the existing virtual port functions are
>>> called to set mac, vlan and port profile.
>> I'm unable to test that part, as I don't have any 802.1QbX capable
>> switches (and it sounds like the design is problematic anyway.)
> The design is still fine for 802.1Qbh.

Yes, my apologies for misinterpreting all the exchanges.

> I have tested it. 802.1Qbh does not
> need a macvtap device. For 802.1Qbg in v2 (was planning on pushing it the
> next hr),

I'll try to review it as quickly as possible.

>  I have put a check for 802.1Qbg and hostdevs and fail as suggested
> by stefan.

I'm quickly learning that I understood much less about 802.1QbX (and in
particular, how it's been implemented) than I thought! (Fortunately, as
a result of all this, I think I now understand it a bit better).

>>> * If virtualport is not specified and device is a sriov virtual function,
>>> - mac is set using IFLA_VF_MAC
>> Success!! I tried this for VFs that have a netdev driver attached, and
>> VFs that don't, and it behaved properly in both cases - when the guest
>> is started, the MAC address is set properly for the guest to use, and
>> when the guest is stopped, the MAC address of that VF is restored to its
>> original value (implying that your code to save the old MAC address
>> works properly).
> Nice. Thanks for trying it out.
>>> * If virtualport is not specified and device is a non-sriov virtual function,
>>> - mac is set using existing SIOCGIFHWADDR (This requires that the
>>>         netdev be present on the host before starting the VM)
>> This one has a problem, at least with my non-sriov hardware (which
>> happens to be the onboard NetXtreme device of a Thinkstation, using the
>> tg3 driver) it appears the MAC address gets reset to its original
>> setting at some point after libvirt changes it. To help understand what
>> happens - assume the device's original MAC address is o:o:o:o:o:o, and
>> my xml looks like this:
>>   <interface type='hostdev' managed='yes'>
>>     <mac address='n:n:n:n:n:n'/>
>>     ...
>>   </interface>
>> When the guest boots up, ifconfig shows there is an interface with mac
>> address o:o:o:o:o:o.
>> Additionally, if I manually change the mac address to p:p:p:p:p:p on the
>> host before starting the guest, when the guest boots, ifconfig shows the
>> mac address as... o:o:o:o:o:o. So, whether or not libvirt is
>> successfully setting the mac address, it's getting reset (probably by
>> the card's firmware).
> Yes this I kind of expected. It depends on the driver. I thought there are
> some drivers that remember the mac address set by SIOCGIFHWADDR. But my
> assumption was totally based on the fact that we wanted to add support for
> all devices. Having the code there just means we try to set the device mac.
> It takes effect only if the hw supports it.

If there was just a way to determine that at runtime, but it seems that
by the time the MAC address has been reset, we are no longer able to
call the ioctl to check the address :-(

>> So perhaps this is another case of wanting to do something that just
>> isn't possible, and the way out is to simply generate an error on domain
>> startup if the netdev being passed through isn't a VF?
> We can do this too. Only support it for sriov vf's.

Yes, if it's going to silently do the wrong thing, maybe we should leave
the SIOCGIFHWADDR code in there for reference, but also add a failure
condition if the card isn't SRIOV.

(I guess this means my effort to make sure USB ethernets were also
supported was kind of pointless, since they're sure to have the same
problems :-P Mostly I only included that support to promote code sharing
and consistency, though, so I'm not really disappointed.)

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