Description of problem:

This is on Rawhide, booting an appliance like this:

/usr/bin/qemu-kvm \
  -drive file=/tmp/test.img,cache=off,if=virtio \
  -m 500 -no-reboot \
  -kernel /tmp/libguestfsJMrUXK/kernel \
  -initrd /tmp/libguestfsJMrUXK/initrd \
  -append 'panic=1 console=ttyS0 udevtimeout=300 noapic acpi=off cgroup_disable=memory selinux=0 guestfs=10.0.2.4:6666 guestfs_verbose=1' \
  -nographic -serial stdio \
  -net channel,6666:unix:/tmp/libguestfsJMrUXK/sock,server,nowait \
  -net user,vlan=0,net=10.0.2.0/8 \
  -net nic,model=virtio,vlan=0 \     <===== NB
  -no-hpet -rtc-td-hack

When the appliance boots, it does this inside the guest:

  /sbin/ifconfig lo 127.0.0.1
  /sbin/ifconfig eth0 10.0.2.10
  /sbin/route add default gw 10.0.2.2
  ping -n -v -c 5 10.0.2.2

Ping fails with:

  PING 10.0.2.2 (10.0.2.2) 56(84) bytes of data.
  From 10.0.2.10 icmp_seq=2 Destination Host Unreachable
  From 10.0.2.10 icmp_seq=3 Destination Host Unreachable
  From 10.0.2.10 icmp_seq=4 Destination Host Unreachable

Also connections from inside the guest fail with:

  connect: Network is unreachable

Previously this was worked fine to set up the network.
However in Rawhide, this fails a lot of the time.

The virtio_net module is loaded, and there are no kernel
errors or other messages to indicate any problem.

If I change the line marked "NB" above to:

  -net nic,model=ne2k_pci,vlan=0

(and obviously load the ne2k-pci driver instead of virtio_net)
then the test *works*.

Note: The only change in the test is replacing virtio with ne2k-pci,
so it does appear to be a problem with virtio somewhere.

Version-Release number of selected component (if applicable):

qemu-0.10.91-0.4.rc1.fc12.x86_64
kernel (in guest) 2.6.31-0.24.rc0.git18.fc11.x86_64

How reproducible:

Not 100% of the time, but quite close to it.

Steps to Reproduce:

With libguestfs:
guestfish -v alloc /tmp/test.img 200M : run