fc12 virsh tap networking problem

[Chiradeep Vittal]

Hi,
On a fresh FC12 system, I am able to create and run KVM-based vms with tap networking
using the qemu-kvm command line but not using virsh.
I have user and group set to "root" in /etc/libvirt/qemu.conf. "user mode
networking" works with virsh, but not tap! selinux is disabled. 

I have this xml:
<domain type='kvm'>
  <name>centos</name>
  <uuid>22d9d573-d82c-c18d-36c0-d3ffef057468</uuid>
  <memory>131072</memory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64'>hvm</type>
  </os>
  <features>
    <acpi/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <devices>
    <emulator>/usr/bin/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <source file='/var/lib/images/centos.5-4.x86-64/centos-small.img'/>
      <target dev='hda' bus='ide'/>
    </disk>
    <interface type='user'>
      <mac address='52:54:00:7e:5b:58'/>
    </interface>
    <interface type='ethernet'>
      <mac address='52:54:00:2e:33:c8'/>
      <script path='/var/lib/images/centos.5-4.x86-64/qemu-ifup'/>
    </interface>
    <graphics type='vnc' port='5910' autoport='no'
listen=''/>
  </devices>
</domain>

This won't start even when I execute virsh as root:
[root@fc12 centos.5-4.x86-64]# virsh -c qemu+unix:///system   create domr.xml 
error: Failed to create domain from domr.xml
error: monitor socket did not show up.: No such file or directory
[root@fc12 centos.5-4.x86-64]# tail -3 /var/log/libvirt/qemu/centos.log 
LC_ALL=C
PATH=/sbin:/usr/sbin:/bin:/usr/bin QEMU_AUDIO_DRV=none
/usr/bin/qemu-kvm -S -M pc-0.11 -m 128 -smp 1 -name centos -uuid
22d9d573-d82c-c18d-36c0-d3ffef057468 -monitor
unix:/var/lib/libvirt/qemu/centos.monitor,server,nowait -boot c -drive
file=/var/lib/images/centos.5-4.x86-64/centos-small.img,if=ide,index=0,boot=on
-net nic,macaddr=52:54:00:7e:5b:58,vlan=0,name=nic.0 -net
user,vlan=0,name=user.0 -net
nic,macaddr=52:54:00:2e:33:c8,vlan=1,name=nic.1 -net
tap,script=/var/lib/images/centos.5-4.x86-64/qemu-ifup,vlan=1,name=tap.0
-serial none -parallel none -usb -vnc :10 -vga cirrus 
warning: could not configure /dev/net/tun: no virtual network emulation
qemu: Could not initialize device 'tap'

'***** But I can execute the same command line and it works!!********
[root@fc12
centos.5-4.x86-64]# LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin
QEMU_AUDIO_DRV=none /usr/bin/qemu-kvm -S -M pc-0.11 -m 128 -smp 1 -name
centos -uuid 22d9d573-d82c-c18d-36c0-d3ffef057468 -monitor
unix:/var/lib/libvirt/qemu/centos.monitor,server,nowait -boot c -drive
file=/var/lib/images/centos.5-4.x86-64/centos-small.img,if=ide,index=0,boot=on
-net nic,macaddr=52:54:00:7e:5b:58,vlan=0,name=nic.0 -net
user,vlan=0,name=user.0 -net
nic,macaddr=52:54:00:2e:33:c8,vlan=1,name=nic.1 -net
tap,script=/var/lib/images/centos.5-4.x86-64/qemu-ifup,vlan=1,name=tap.0
-serial none -parallel none -usb -vnc :10 -vga cirrus &
[2] 4543

[root@fc12 centos.5-4.x86-64]# ps -ef | grep qemu
root      4543  3449  0 19:02 pts/12  
00:00:00 /usr/bin/qemu-kvm -S -M pc-0.11 -m 128 -smp 1 -name centos
-uuid 22d9d573-d82c-c18d-36c0-d3ffef057468 -monitor
unix:/var/lib/libvirt/qemu/centos.monitor,server,nowait -boot c -drive
file=/var/lib/images/centos.5-4.x86-64/centos-small.img,if=ide,index=0,boot=on
-net nic,macaddr=52:54:00:7e:5b:58,vlan=0,name=nic.0 -net
user,vlan=0,name=user.0 -net
nic,macaddr=52:54:00:2e:33:c8,vlan=1,name=nic.1 -net
tap,script=/var/lib/images/centos.5-4.x86-64/qemu-ifup,vlan=1,name=tap.0
-serial none -parallel none -usb -vnc :10 -vga cirrus

[Mark McLoughlin]

On Tue, 2009-12-08 at 19:43 -0800, Chiradeep Vittal wrote:
>  Hi,
>  On a fresh FC12 system, I am able to create and run KVM-based vms with
>  tap networking using the qemu-kvm command line but not using virsh.
>  I have user and group set to "root" in /etc/libvirt/qemu.conf. "user
>  mode networking" works with virsh, but not tap! selinux is disabled.  
Okay, you've ruled out the most likely culprits :-)

Is this a stock Fedora 12 kernel?

>  I have this xml:
>  <domain type='kvm'>
>    <name>centos</name>
>    <uuid>22d9d573-d82c-c18d-36c0-d3ffef057468</uuid>
>    <memory>131072</memory>
>    <vcpu>1</vcpu>
>    <os>
>      <type arch='x86_64'>hvm</type>
>    </os>
>    <features>
>      <acpi/>
>      <pae/>
>    </features>
>    <clock offset='utc'/>
>    <devices>
>      <emulator>/usr/bin/qemu-kvm</emulator>
>      <disk type='file' device='disk'>
>        <source
>  file='/var/lib/images/centos.5-4.x86-64/centos-small.img'/>
>        <target dev='hda' bus='ide'/>
>      </disk>
>      <interface type='user'>
>        <mac address='52:54:00:7e:5b:58'/>
>      </interface>
>      <interface type='ethernet'>
>        <mac address='52:54:00:2e:33:c8'/>
>        <script path='/var/lib/images/centos.5-4.x86-64/qemu-ifup'/> 
Try adding:

        <target dev="mytap0"/>

here and seeing if that helps?

>      </interface>
>      <graphics type='vnc' port='5910' autoport='no'
> listen=''/>
>    </devices>
>  </domain>
>  
>  This won't start even when I execute virsh as root:
>  [root@fc12 centos.5-4.x86-64]# virsh -c qemu+unix:///system   create
>  domr.xml 
>  error: Failed to create domain from domr.xml
>  error: monitor socket did not show up.: No such file or directory
>  [root@fc12 centos.5-4.x86-64]# tail
>  -3 /var/log/libvirt/qemu/centos.log 
>  LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin
>  QEMU_AUDIO_DRV=none /usr/bin/qemu-kvm -S -M pc-0.11 -m 128 -smp 1
>  -name centos -uuid 22d9d573-d82c-c18d-36c0-d3ffef057468 -monitor
>  unix:/var/lib/libvirt/qemu/centos.monitor,server,nowait -boot c -drive
>  file=/var/lib/images/centos.5-4.x86-64/centos-small.img,if=ide,index=0,boot=on -net
> nic,macaddr=52:54:00:7e:5b:58,vlan=0,name=nic.0 -net user,vlan=0,name=user.0 -net
> nic,macaddr=52:54:00:2e:33:c8,vlan=1,name=nic.1 -net
> tap,script=/var/lib/images/centos.5-4.x86-64/qemu-ifup,vlan=1,name=tap.0 -serial none
> -parallel none -usb -vnc :10 -vga cirrus 
>  warning: could not configure /dev/net/tun: no virtual network
>  emulation
>  qemu: Could not initialize device 'tap' 
The code here is quite straightforward:

  http://repo.or.cz/w/qemu-kvm/fedora.git/blob/HEAD:/net.c#l1801

all it's doing is configuring the tap device flags and name using the
TUNSETIFF ioctl

You could try strace e.g.

  $> service libvirtd stop
  $> strace -f libvirtd > t.log 2>&1

that might give you more insight to what qemu is doing when it calls
TUNSETIFF

>  '***** But I can execute the same command line and it
> works!!********
>  [root@fc12 centos.5-4.x86-64]# LC_ALL=C
>  PATH=/sbin:/usr/sbin:/bin:/usr/bin
>  QEMU_AUDIO_DRV=none /usr/bin/qemu-kvm -S -M pc-0.11 -m 128 -smp 1
>  -name centos -uuid 22d9d573-d82c-c18d-36c0-d3ffef057468 -monitor
>  unix:/var/lib/libvirt/qemu/centos.monitor,server,nowait -boot c -drive
>  file=/var/lib/images/centos.5-4.x86-64/centos-small.img,if=ide,index=0,boot=on -net
> nic,macaddr=52:54:00:7e:5b:58,vlan=0,name=nic.0 -net user,vlan=0,name=user.0 -net
> nic,macaddr=52:54:00:2e:33:c8,vlan=1,name=nic.1 -net
> tap,script=/var/lib/images/centos.5-4.x86-64/qemu-ifup,vlan=1,name=tap.0 -serial none
> -parallel none -usb -vnc :10 -vga cirrus &
>  2] 4543 
I've no idea why this works, but doesn't work when launched from libvirt

Cheers,
Mark.