xenstore watches not firing for external-to-xend code using xen.xend.xenstore classes

xenstore watches not firing for external-to-xend code using xen.xend.xenstore classes

[Charles Duffy]

I'm trying to write a simple xenstore-based watchdog, as discussed 
previously on this list (quite some time ago -- it got pushed to the 
back of my priority list for a bit).

In any event, I'm trying to use the below code to test the ability of a 
program external to xend to place watches on xenstore. However, the 
callbacks aren't firing except on initial startup, either when I use 
xenstore-write to update /tool/watchdog/test or when I start or shutdown 
domains (to invoke the @introduceDomain or @releaseDomain triggers). 
Obviously I'm missing something here. If this is a simple error on my 
part, or if I'm expecting behaviour that wasn't designed for, I'd 
appreciate a pointer or two.

Thanks!

---------

#!/usr/bin/env python

from xen.xend.xenstore.xstransact import xstransact
from xen.xend.xenstore.xswatch import xswatch

from pprint import pprint
import time, logging
logging.basicConfig(level=logging.DEBUG)

TROOT = '/tool/watchdog'

class XenWatchdog:
   def __init__(self):
     xswatch('@releaseDomain', self.callback, 'releaseDomain')
     xswatch('@introduceDomain', self.callback, 'introduceDomain')
     xswatch('%(TROOT)s/test' % locals(), self.callback, 'test')
   def callback(self, *args, **kwargs):
     pprint([ 'onReleaseDomain', args, kwargs ])

Re: xenstore watches not firing for external-to-xend code using xen.xend.xenstore classes

[Ewan Mellor]

On Thu, Feb 09, 2006 at 10:35:50AM -0600, Charles Duffy wrote:

> I'm trying to write a simple xenstore-based watchdog, as discussed 
> previously on this list (quite some time ago -- it got pushed to the 
> back of my priority list for a bit).
>
> [Snip]
>
> 
> #!/usr/bin/env python
> 
> from xen.xend.xenstore.xstransact import xstransact
> from xen.xend.xenstore.xswatch import xswatch
> 
> from pprint import pprint
> import time, logging
> logging.basicConfig(level=logging.DEBUG)
> 
> TROOT = '/tool/watchdog'
> 
> class XenWatchdog:
>   def __init__(self):
>     xswatch('@releaseDomain', self.callback, 'releaseDomain')
>     xswatch('@introduceDomain', self.callback, 'introduceDomain')
>     xswatch('%(TROOT)s/test' % locals(), self.callback, 'test')
>   def callback(self, *args, **kwargs):
>     pprint([ 'onReleaseDomain', args, kwargs ])

callback needs to return True to say that it would like to stay
registered.  As it is, you are returning nothing, which looks like
False, which means your callback is deregistered after the first call.

This changed a couple of months ago, and it still bites people.  (My
kingdom for a static type system ;-)

Ewan.

Re: xenstore watches not firing for external-to-xend code using xen.xend.xenstore classes

[Charles Duffy]

Ewan Mellor wrote:
> callback needs to return True to say that it would like to stay
> registered.  As it is, you are returning nothing, which looks like
> False, which means your callback is deregistered after the first call.
>   
That was it, indeed.

Thanks!