Xen devel - Apr 2007 - Error: Device 0 (vkbd) is already connected.

Hi,

   Is vfb working well lately?  I thought I''d test it out on ia64 and
it
works great, but only once per boot.  If I stop the domain and restart
it, I get the following:

Error: Device 0 (vkbd) is already connected.

To make sure this isn''t an ia64 anomaly, I tried it on an x86_64
system.
Same thing, works the first time, reboot the domain and it''s broken.  I
see someone reported a similar issue last month, but there was no
response:

http://lists.xensource.com/archives/html/xen-devel/2007-03/msg01141.html

The backtrace in xend.log looks like this:

[2007-04-11 15:23:07 2659] ERROR (__init__:1072) XendDomainInfo.initDomain: exce
ption occurred
Traceback (most recent call last):
  File "//usr/lib/python/xen/xend/XendDomainInfo.py", line 1518, in
_initDomain
    self._createDevices()
  File "//usr/lib/python/xen/xend/XendDomainInfo.py", line 1316, in
_createDevices
    devid = self._createDevice(devclass, config)
  File "//usr/lib/python/xen/xend/XendDomainInfo.py", line 1292, in
_createDevice
    return self.getDeviceController(deviceClass).createDevice(devConfig)
  File "//usr/lib/python/xen/xend/server/DevController.py", line 111,
in createDevice
    raise VmError("Device %s is already connected." % dev_str)
VmError: Device 0 (vkbd) is already connected.

My domain config file has the following options to enable vfb:

vfb = [ ''type=vnc, vnclisten=0.0.0.0, vncunused=1'' ]
extra = "console=ttyS0 xencons=ttyS video=xenfb"

Is anyone able to make this work reliably more than once?  Thanks,

	Alex

-- 
Alex Williamson                             HP Open Source & Linux Org.


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Hi,


I can confirm this failure using 3.0.5-rc2 hypervisor and tools with a
3.0.4-1 2.6.16.38 Gentoo guest on i386.
After dom0 boot, the domU boots fine, vncfb runs fine.
If I halt the domU, I can''t boot it again and get this error :
Device 0 (vkbd) is already connected.

All was running fine with 3.0.4-1 hypervisor and tools and same
guest/config.


Regards,
Cédric

2007/4/11, Alex Williamson
<alex.williamson@hp.com>:
>
> Hi,
>
>    Is vfb working well lately?  I thought I''d test it out on ia64
and it
> works great, but only once per boot.  If I stop the domain and restart
> it, I get the following:
>
> Error: Device 0 (vkbd) is already connected.
>
> To make sure this isn''t an ia64 anomaly, I tried it on an x86_64
system.
> Same thing, works the first time, reboot the domain and it''s
broken.  I
> see someone reported a similar issue last month, but there was no
> response:
>
> http://lists.xensource.com/archives/html/xen-devel/2007-03/msg01141.html
>
> The backtrace in xend.log looks like this:
>
> [2007-04-11 15:23:07 2659] ERROR (__init__:1072) XendDomainInfo.initDomain:
> exce
> ption occurred
> Traceback (most recent call last):
>   File "//usr/lib/python/xen/xend/XendDomainInfo.py", line 1518,
in
> _initDomain
>     self._createDevices()
>   File "//usr/lib/python/xen/xend/XendDomainInfo.py", line 1316,
in
> _createDevices
>     devid = self._createDevice(devclass, config)
>   File "//usr/lib/python/xen/xend/XendDomainInfo.py", line 1292,
in
> _createDevice
>     return self.getDeviceController(deviceClass).createDevice(devConfig)
>   File "//usr/lib/python/xen/xend/server/DevController.py", line
111, in
> createDevice
>     raise VmError("Device %s is already connected." % dev_str)
> VmError: Device 0 (vkbd) is already connected.
>
> My domain config file has the following options to enable vfb:
>
> vfb = [ ''type=vnc, vnclisten=0.0.0.0, vncunused=1'' ]
> extra = "console=ttyS0 xencons=ttyS video=xenfb"
>
> Is anyone able to make this work reliably more than once?  Thanks,
>
>         Alex
>
> --
> Alex Williamson                             HP Open Source & Linux Org.
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>

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On Wed, Apr 11, 2007 at 03:32:19PM -0600, Alex Williamson
wrote:
> Hi,
> 
>    Is vfb working well lately?  I thought I''d test it out on ia64
and it
> works great, but only once per boot.  If I stop the domain and restart
> it, I get the following:
> 
> Error: Device 0 (vkbd) is already connected.
> 
> To make sure this isn''t an ia64 anomaly, I tried it on an x86_64
system.
> Same thing, works the first time, reboot the domain and it''s
broken.  I
> see someone reported a similar issue last month, but there was no
> response:
> 
> http://lists.xensource.com/archives/html/xen-devel/2007-03/msg01141.html
> 
> The backtrace in xend.log looks like this:
> 
> [2007-04-11 15:23:07 2659] ERROR (__init__:1072) XendDomainInfo.initDomain:
exce
> ption occurred
> Traceback (most recent call last):
>   File "//usr/lib/python/xen/xend/XendDomainInfo.py", line 1518,
in _initDomain
>     self._createDevices()
>   File "//usr/lib/python/xen/xend/XendDomainInfo.py", line 1316,
in _createDevices
>     devid = self._createDevice(devclass, config)
>   File "//usr/lib/python/xen/xend/XendDomainInfo.py", line 1292,
in _createDevice
>     return self.getDeviceController(deviceClass).createDevice(devConfig)
>   File "//usr/lib/python/xen/xend/server/DevController.py", line
111, in createDevice
>     raise VmError("Device %s is already connected." % dev_str)
> VmError: Device 0 (vkbd) is already connected.
> 
> My domain config file has the following options to enable vfb:
> 
> vfb = [ ''type=vnc, vnclisten=0.0.0.0, vncunused=1'' ]
> extra = "console=ttyS0 xencons=ttyS video=xenfb"
> 
> Is anyone able to make this work reliably more than once?  Thanks,
I''ve done some testing & this is (reasonably) reproducable on x86
too. On
some occassions I can''t even get it to start once, other times it works
a couple of times.

After some debugging I think I''ve identified a race condition:

 1. XendDomainInfo._createDevices() gets a list of devices to be created
    from XendConfig.ordered_device_refs()

    On a simple guest, this has 4 devices, vfb, vbd, vif, vkbd - in that
    order

 2. It iterates over those devices, creating the appropriate DevController
    subclass instance, and then calling createDevice() on that object.

 3. When createDevice() is called on the vfb  device, it spawns xen-vncfb
    daemon.

 4. During startup xen-vncfb writes into the backend paths

            /local/domain/0/backend/vfb/0

     And

            /local/domain/0/backend/vkbd/0

 5. When createDevice() is called on the vkbd device in XenD, if the 2nd
    xenstore path write from step 4 has occurred, then you''ll hit the
    ''Device 0 (vkbd) is already connected'' error. If the 2nd
path write
    didn''t complete yet then everything is fine.


I think the reason it often works once after boot is that loading xen-vncfb
from disk the first time around is just enough of a slow down to ensure step 
5 occurs before the 2nd xenstore write in step 4 has occurred.


The key seems to be to ensure the vkbd device is initialized in xenstore
before the vfb device - this ensures all the xenstored setup from XenD
is complete before the xen-vncfb daemon starts. I''m attaching a patch
which implements this - I''ve been able to create & destroy a domain
many
times over with this patch & never hit the error message anymore.


   Signed-off-by: Daniel P. Berrange <berrange@redhat.com>


Regards,
Dan.
-- 
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