Re: [Wg-openstack] [Xen-devel] tap device name for emulated NIC too long

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Nov 30, 2016 at 06:38:45PM -0700, Jim Fehlig wrote:
> Hi All,

.. crickets..
> 
> During the last Wg-openstack meetup we briefly discussed a long-standing bug
> when using Xen+libvirt+OpenStack with Neutron networking
> 
> https://bugs.launchpad.net/nova/+bug/1450465
> 
> The bug was also discussed on this list with no resolution
> 
> https://lists.xenproject.org/archives/html/xen-devel/2015-06/msg04116.html
> 
> To summarize: the tap device name for an emulated NIC is too long after
> libxl appends '-emu' to the name provided by Neutron. Some proposed fixes
> include
> 
> 1. Shorten '-emu' to just '-e', avoiding IFNAMSIZ limit. But users are free
> to provide a name that already occupies the full IFNAMSIZ. Also, the
> user-provided name may be used in rules, filters, etc. elsewhere in the
> network, so modifying it at all seems questionable.

+1
> 
> 2. Change OpenStack to not exceed IFNAMSIZ-4 when specifying Xen vif name.
> This could be proposed to the Neutron devs, but IMO adding such Xen-specific
> hacks in OpenStack is undesirable.
> 
> 3. Change the Xen default vif type from 'ioemu' to 'vif' (see
> docs/misc/xl-network-configuration.markdown), which avoids creating an
> emulated device. (Note: such a change could be made in Xen or libvirt.) But
> I think this is a no-go. I'd suspect it would result in a lot of broken
> configurations. E.g. a guest may not have PV drivers and is relying on the
> emulated device. Or the guest may be configured to network boot, in which
> case the emulated device would be needed for PXE [0].
> 
> We (the Wg-openstack folks) would like to hear your opinions on these
> proposals, or alternatives for fixing this bug.
> 
> Regards,
> Jim
> 
> [0] iPXE claims support for Xen netfront devices, but I've not yet got it to
> work: http://lists.ipxe.org/pipermail/ipxe-devel/2014-July/003674.html
> 
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> https://lists.xen.org/xen-devel

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