[Bug 430652] [NEW] /etc/qemu-ifup script regression - fails to find bridge interface

[Dominic Evans]

Public bug reported:

Binary package hint: qemu-kvm

= Abstract

The /etc/qemu-ifup script used by `-net tap` seems to have regressed in
0.11.0~rc2-0ubuntu4 and no longer functions correctly on a machine where
it previously worked.

= Description

/etc/qemu-ifup used to hardcode the bridge interface to br0. Now it
attempts to found this out using an awk of the routing table. This fails
on my system in the following way:

$ sudo qemu rhel5-1.img -net nic -net tap -m 512 -name RHEL1 -vga std
bridge 100 does not exist!
/etc/qemu-ifup: could not launch network script
qemu: Could not initialize device 'tap'

The qemu-ifup script is attempted to find `br0` via the following cmd (which grabs the last column on the line that starts with 'default')
  switch=$(/sbin/ip route list | awk '/^default / { print $NF }')

(ip addresses modified)
$ /sbin/ip route list
74.125.127.0/24 dev br0  proto kernel  scope link  src 74.125.127.11 
169.254.0.0/16 dev br0  scope link  metric 1000 
default via 74.125.127.1 dev br0  metric 100

Obviously in my case that gives '100', which is incorrect.

** Affects: qemu-kvm (Ubuntu)
     Importance: Undecided
         Status: New

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/etc/qemu-ifup script regression - fails to find bridge interface
https://bugs.launchpad.net/bugs/430652
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