[Xen-users] Hotplug scripts not working / problem with loopback driver

[Craig Webster <craig@xxxxxxxxxx>]

Hi list,

I'm having a bit of an annoying problem which, being new to Xen and  
the loopback device, I have no idea how to fix.
Everything was running along fine with 4 VMs, I attempted to add a  
5th VM and it couldn't connect to the backend devices. A quick Google  
suggested that increasing the max_loop parameter for the kernel  
(loopback driver is compiled in, not a module) would fix this so I  
added that param to my grub.conf and rebooted.
When I tried to start any of the previously working VMs I now get  
this happening:
  saturn vm # xm create subversion.cfg -c
  Using config file "subversion.cfg".
  Error: Device 769 (vbd) could not be connected. Hotplug scripts  
not working.
  saturn vm # xm destroy subversion
  saturn vm # xm create subversion.cfg -c
  Using config file "subversion.cfg".
  Error: Device 770 (vbd) could not be connected. Backend device not  
found.
  saturn vm # xm destroy subversion
  saturn vm # xm create subversion.cfg -c
  Using config file "subversion.cfg".
  Error: Device 770 (vbd) could not be connected. Backend device not  
found.
I have since tried removing the max_loop param from my grub.conf and  
rebooting but the same problem keeps coming up.
Google suggested removing the memory limit on dom0 but that didn't  
make any difference; I still got the same error.
Looking at the logs it appears that there's something wrong with my  
loopbacks or block hotplug script, but I don't know enough to know  
what to Google for next.
Commenting out the disk parameter in my vm config file allows the  
boot process to get much further (until it tries to mount the disks).
These are the log entries:
  saturn vm # tail /var/log/xen-hotplug.log
  mkdir: cannot create directory `/var/run/xen-hotplug/block': File  
exists
  mkdir: cannot create directory `/var/run/xen-hotplug/block': File  
exists
  [... repeated lots ...]
  mkdir: cannot create directory `/var/run/xen-hotplug/block': File  
exists
  ioctl: LOOP_SET_FD: Device or resource busy

  saturn vm # tail /var/log/xend.log
      return self.dom.waitForDevices()
    File "/usr/lib64/python2.4/site-packages/xen/xend/ 
XendDomainInfo.py", line 1343, in waitForDevices
      self.waitForDevices_(c)
    File "/usr/lib64/python2.4/site-packages/xen/xend/ 
XendDomainInfo.py", line 971, in waitForDevices_
      return self.getDeviceController(deviceClass).waitForDevices()
    File "/usr/lib64/python2.4/site-packages/xen/xend/server/ 
DevController.py", line 135, in waitForDevices
      return map(self.waitForDevice, self.deviceIDs())
    File "/usr/lib64/python2.4/site-packages/xen/xend/server/ 
DevController.py", line 151, in waitForDevice
      raise VmError("Device %s (%s) could not be connected. "
  VmError: Device 770 (vbd) could not be connected. Backend device  
not found.
My subversion.cfg looks like this:

  saturn vm # cat subversion.cfg
  kernel = "/var/vm/vmlinuz-2.6-xenU"
  memory = 64
  ip = "aaa.bbb.ccc.ddd" # This is a public IP in the cfg file
  netmask = "255.255.255.192"
  gateway = "aaa.bbb.ccc.ddd" # As is this
  vif = ['bridge=xenbr0']
  name = "subversion"
  disk = ['file:/var/vm/subversion-hd.img,sda1,w','file:/var/vm/ 
subversion-swap.img,sda2,w']
  root = "/dev/sda1 ro"

If you have any suggestions which could help me get these VMs running  
again they would be much appreciated.
Cheers,
Craig

ps apologies for the length of the post -- wanted to include as much  
information as possible.
--
Craig Webster | t: +44 (0)131 516 8595 | e: craig@xxxxxxxxxx
Xeriom.NET    | f: +44 (0)131 661 0689 | w: http://xeriom.net

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