Error: Device 768 (vbd) could not be connected. Backend device not found.

Error: Device 768 (vbd) could not be connected. Backend device not found.

[Jonathan M. McCune]

Hello,

I am getting this error when I try to start an HVM guest on an AMD 
Sahara system.  The xen-unstable-hvm.hg revision 8724 works fine.  I 
tried to upgrade to xen-unstable.hg revision 9668.  I got 9668 to boot 
using 'yaird' to build the initrd for the -xen kernel. I can 
successfully start a paravirtualized guest, but I am now having trouble 
starting an HVM guest.  The error message is:

Error: Device 768 (vbd) could not be connected. Backend device not found.

I googled a bit and other people have seen this error, but no solutions
seem to be presented.

Each attempt to start the domain puts a line like the following in
/var/log/xen-hotplug.log (The '8' here is the domain ID):

xenstore-read: couldn't read path backend/vbd/8/768/node

Here is my config file:

kernel = "/usr/lib/xen/boot/hvmloader"
builder='hvm'
memory = 260
name = "Sarge"
disk = [ 'file:/sarge/disk.img,ioemu:hda,w' ]
vif = [ 'type=ioemu, mac=00:14:bf:52:df:5e, bridge=xenbr0' ]
device_model = '/usr/lib/xen/bin/qemu-dm'
memmap = '/usr/lib/xen/boot/mem-map.sxp'
boot='c'
sdl=1
vnc=0

I have made sure that xend and xenstored are running, but I'm not sure 
what else to check (it works on the older Xen!).  Any suggestions would 
be greatly appreciated.

Thanks,
-Jon

Re: Error: Device 768 (vbd) could not be connected. Backend device not found.

[Ryan Harper]

* Jonathan M. McCune <jonmccune@cmu.edu> [2006-04-19 09:14]:
> Hello,
> 
> I am getting this error when I try to start an HVM guest on an AMD 
> Sahara system.  The xen-unstable-hvm.hg revision 8724 works fine.  I 
> tried to upgrade to xen-unstable.hg revision 9668.  I got 9668 to boot 
> using 'yaird' to build the initrd for the -xen kernel. I can 
> successfully start a paravirtualized guest, but I am now having trouble 
> starting an HVM guest.  The error message is:
> 
> Error: Device 768 (vbd) could not be connected. Backend device not found.
<snip>
> disk = [ 'file:/sarge/disk.img,ioemu:hda,w' ]

I got this when the loop driver (which is a module in -xen kernel config
is used) wasn't loaded.  Try modprobe loop, and re-run your create
command.


-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com

RE: Error: Device 768 (vbd) could not be connected. Backend device not found.

[Petersson, Mats]

> -----Original Message-----
> From: xen-devel-bounces@lists.xensource.com 
> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of 
> Jonathan M. McCune
> Sent: 19 April 2006 15:12
> To: xen-users@lists.xensource.com; xen-devel@lists.xensource.com
> Subject: [Xen-devel] Error: Device 768 (vbd) could not be 
> connected. Backend device not found.
> 
> Hello,
> 
> I am getting this error when I try to start an HVM guest on 
> an AMD Sahara system.  The xen-unstable-hvm.hg revision 8724 
> works fine.  I tried to upgrade to xen-unstable.hg revision 
> 9668.  I got 9668 to boot using 'yaird' to build the initrd 
> for the -xen kernel. I can successfully start a 
> paravirtualized guest, but I am now having trouble starting 
> an HVM guest.  The error message is:
> 
> Error: Device 768 (vbd) could not be connected. Backend 
> device not found.
> 
> I googled a bit and other people have seen this error, but no 
> solutions seem to be presented.
> 
> Each attempt to start the domain puts a line like the 
> following in /var/log/xen-hotplug.log (The '8' here is the domain ID):
> 
> xenstore-read: couldn't read path backend/vbd/8/768/node
> 
> Here is my config file:
> 
> kernel = "/usr/lib/xen/boot/hvmloader"
> builder='hvm'
> memory = 260
> name = "Sarge"
> disk = [ 'file:/sarge/disk.img,ioemu:hda,w' ] vif = [ 
> 'type=ioemu, mac=00:14:bf:52:df:5e, bridge=xenbr0' ] 
> device_model = '/usr/lib/xen/bin/qemu-dm'
> memmap = '/usr/lib/xen/boot/mem-map.sxp'
> boot='c'
> sdl=1
> vnc=0
> 
> I have made sure that xend and xenstored are running, but I'm 
> not sure what else to check (it works on the older Xen!).  
> Any suggestions would be greatly appreciated.

Check that your qemu-dm is actually where you've got it specified. I can
think of several times when I've had problems because the qemu-dm isn't
where it should've been... 

Also check that /sarge/disk.img is actually present... 

Are you running a 32-bit or 64-bit hypervisor? Did you by any chance
change from one to the other? If so, did you clean out the old one
first? I've had several problems caused by the 64-bit build finding
(old) 32-bit components and behaving really weird as a consequence... 

--
Mats
> 
> Thanks,
> -Jon
> 
> 
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