[Pkg-xen-devel] Bug#658305: Prevent silently failing on duplicate vifname

[Hans van Kranenburg]

Package: xen-utils-common
Version: 4.1.2-3
Severity: normal

When configurating a duplicate custom vifname for interfaces in the Xen
dom0 that are added to a bridge (which is obviously a configuration
error), the hotplug scripts fail silently to rename the new vifX.0 to
the custom vifname, if it's already existing.

The result of this, is that the domU will start normally, but no network
traffic between domU and the dom0 bridge is possible, because the vifX.0
never gets added to the bridge.

Worse... when doing xm shutdown on the newly created domU, while
investigating the issue, the interface of another running domU gets shut
down, and remains hanging around in a DOWN state, because it cannot be
removed (the other unrelated domU is still running, but succesfully made
unavailable on the network!).

When starting the new domU again, the interface of the other domU will
be added to the bridge again, and while looking at the output of brctl
show, tcpdump and ping, which make no sense, because everything will
seem to be right, nagios will notify you of another host being down. :|

The attached patch makes sure the script exits with an error when the
vifname is already in use. The patch applies to unstable, but it's very
easy to port to xen-utils-common in squeeze, which I'll be doing myself
(been there, done that).

The effect, when I try to configure a vifname of "pietje" for two domU's
looks like:

mu.mgt.xs4.mendix.net:/etc/xen/guests 2-# xm create -c tomato
Using config file "./tomato".
mu.mgt.xs4.mendix.net:/etc/xen/guests 2-# Error: Device 0 (vif) could
not be connected. Cannot rename interface vif40.0. An interface with
name pietje already exists.

Please consider adding the patch, and/or sending it upstream.

Thanks!

-- 
Hans van Kranenburg - System / Network Engineer
T +31 (0)10 2760434 | hans.van.kranenburg at mendix.com | www.mendix.com
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