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Revision 85dde9a9


Added by Markus Armbruster over 9 years ago

Fix netdev name lookup in -device, device_add, netdev_del

qemu_find_netdev() looks up members of non_vlan_clients by name. It
happily returns the first match. Trouble is the names need not be

non_vlan_clients contains host parts (netdevs) and guest parts (NICs).

Netdevs have unique names: a netdev's name is a (mandatory)
qemu_netdev_opts ID, and these are unique.

NIC names are not unique. If a NIC has a qdev ID (which is unique),
that's its name. Else, we make up a name. The made-up names are
unique, but they can clash with qdev IDs. Even if NICs had unique
names, they could still clash with netdev names.

Callers of qemu_find_netdev():

  • net_init_nic() wants a netdev. It happens to work because it runs
    before NICs get added to non_vlan_clients.
  • do_netdev_del() wants a netdev. If it gets a NIC, it complains and
    fails. Bug: a netdev with the same name that comes later in
    non_vlan_clients can't be deleted:

    $ qemu-system-x86_64 -nodefaults -vnc :0 -S -monitor stdio -netdev user,id=hostnet0 -device virtio-net-pci,netdev=hostnet0,id=virtio1
    (qemu) netdev_add user,id=virtio1
    (qemu) info network
    Devices not on any VLAN:
    hostnet0: net=, restricted=n peer=virtio1
    virtio1: model=virtio-net-pci,macaddr=52:54:00:12:34:56 peer=hostnet0
    virtio1: net=, restricted=n
    (qemu) netdev_del virtio1
    Device 'virtio1' not found

  • parse_netdev() wants a netdev. If it gets a NIC, it gets confused.
    With the test setup above:

    (qemu) device_add virtio-net-pci,netdev=virtio1
    Property 'virtio-net-pci.netdev' can't take value 'virtio1', it's in use

    You can even connect two NICs to each other:

    $ qemu-system-x86_64 -nodefaults -vnc :0 -S -monitor stdio -device virtio-net-pci,id=virtio1 -device e1000,netdev=virtio1
    Devices not on any VLAN:
    virtio1: model=virtio-net-pci,macaddr=52:54:00:12:34:56 peer=e1000.0
    e1000.0: model=e1000,macaddr=52:54:00:12:34:57 peer=virtio1
    (qemu) q
    Segmentation fault (core dumped)
  • do_set_link() works fine for both netdevs and NICs. Whether it
    really makes sense for netdevs is debatable, but that's outside this
    patch's scope.

Change qemu_find_netdev() to return only netdevs. This fixes the
netdev_del and device_add/-device bugs demonstrated above.

To avoid changing set_link, make do_set_link() search non_vlan_clients
by hand instead of calling qemu_find_netdev().

Signed-off-by: Markus Armbruster <>
Signed-off-by: Michael S. Tsirkin <>


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