bug#24156: QEMU '-net bridge' --> "qemu-system-x86_64: -net bridge: bridge helper failed"

[myglc2]

Motivation: bridging or routing is required to enable a connection to be
made inward to a QEMU VM. TAP seems like the best of the available
solutions. But connecting to a TAP device produces an error when the
QEMU bridge helper fails.

Example:

address@hidden ~/src/vmb$ qemu-system-x86_64 -net user -net bridge -net 
nic,model=virtio -enable-kvm -m 4096 -k en-us -display curses 
/home/g1/src/vmb/tmp/img6/vm.img
failed to parse default acl file 
`/gnu/store/1072khbm9124a8a1pyyyw4mr1p12jsfq-qemu-2.6.0/etc/qemu/bridge.conf'
qemu-system-x86_64: -net bridge: bridge helper failed

This error was produced with the attached 'img-tap' script. e.g., to
build the vm ...

./img-tap mk 1

To (attempt to) run the vm ..

./img-tap run 1


Running Guix built from git checkout on GuixSD:
stat ~/.config/guix/latest | grep File:
  File: '/home/g1/.config/guix/latest' -> '../../src/guix'
address@hidden ~/src/vmb$ git -C ~/.config/guix/latest describe
v0.11.0-242-g7ccb874

img-tap
Description: Binary data