Hi All,
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.
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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