Re: [Wg-openstack] Minutes from Sept 21 Openstack WG meeting

[Jim Fehlig <jfehlig@xxxxxxxx>]

On 09/28/2016 06:46 AM, Lars Kurth wrote:
>
> On 23/09/2016 03:59, "Jim Fehlig" <jfehlig@xxxxxxxx> wrote:
>
>> On 09/22/2016 09:51 AM, Lars Kurth wrote:
>>>> On 22 Sep 2016, at 16:45, Jim Fehlig <jfehlig@xxxxxxxx> wrote:
>>>>
>>>> On 09/21/2016 11:25 AM, Lars Kurth wrote:
>>>>> === Stuck stuff ===
>>>>>
>>>>> * https://bugs.launchpad.net/nova/+bug/1450465 (no-one looking at
>>>>> that)
>>>>> Joao: not sure how this can be fixed
>>>>> Joao: on some Nova releases this works, but with Neutron it doesn't
>>>>> work
>>>>> Joao: issue with OpenStack assumptions
>>>>> Jim: The only way it solve this is to increase the buffer size
>>>>> Joao: any Xen related fix would create a backwards compatibility issue
>>>>> Jim: not able to specify "want to have PV only", "want to have" ...
>>>>> the
>>>>> default getting both to os hard to change the default ...
>>>>> Jim: instance fails to start because the name is too long we fail the
>>>>> whole thing
>>>>> Joao: name is taken straight from a UID
>>>>>
>>>>> ACTION: Lars it chat to Bob Ball / Platform Team to see whether how
>>>>> XS is
>>>>> working around this or whether there is a way to fix this
>>> I brought this up, and Ian Jackson is not opposed to provide an option
>>> in libxl that allows to optionally provide a custom name for vif's or an
>>> option which leads the generation of a shorter name. Not sure whether
>>> this will solve the problem, but if it does, you may want to quickly
>>> chat to him on IRC.
>> Custom names are already available via the ifname field of
>> libxl_device_nic
>> structure. OpenStack nova specifies names such as 'tap695cf459-b0'. For
>> HVM
>> domains, in addition to the PV NIC, libxl will also create an emulated
>> NIC. The
>> tap device for the emulated NIC gets '-emu' appended to the specified
>> name.  The
>> resulting name 'tap695cf459-b0-emu' is 18 characters, which on linux
>> exceeds 16
>> defined by IFNAMSIZ. The issue was previously discussed and there seemed
>> to be a
>> slight preference to fixing it in nova and neutron
>>
>> http://www.gossamer-threads.com/lists/xen/devel/386076
>>
>> I'm still a bit skeptical pushing the fix to libxl applications.
> Looking at the thread, it was not clear to me whether this was the outcome
> of the thread. My understanding is that we don't know whether shortening
> the name (from "-emu" to "-e"), would actually fully fix the issue and not
> just move it elsewhere. Is this correct?

Shortening the suffix appended to the user-provided name would work, assuming
IFNAMSIZ-name is big enough for the suffix. But there is nothing preventing
users from specifying a name==IFNAMSIZ, in which case there is no room for
appending a suffix.

Another unanswered question was whether the name was also used in some rules or
filters elsewhere in the system. E.g. in an iptables rule or an openvswitch port
profile or the like. Appending a suffix to the name could break such rules or
filters.

Regards,
Jim


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