Xen devel - May 2010 - Problem starting stubdoms past a domid of 257 + fix

I''m running Xen 4.0.1-rc1-pre (21122:7d1d4abd8b44). In this version,
and in all other Xen 3.5-unstable + versions that I''ve looked at, is
this function in XendDomainInfo.py:

    def getStubdomDomid(self):
        dom_list = xstransact.List(''/local/domain'')
        for d in dom_list:
            target = xstransact.Read(''/local/domain/'' + d +
''/target'')
            if target is not None and int(target) is self.domid :
                return int(d)
        return None

The bolded line has a bug in it, unfortunately. This function is used in domain
destruction, and destruction works properly when a domain has a stubdom, but
only until it reaches a domid of around 257. Past that, it breaks. This can be
easily seen by simply starting a bunch of HVMs with stubdoms (I tested by
creating + destroying the same one, over and over).

What''s interesting is that the function works at all -- "is"
really does not seem to be the right comparator to use here.

The fix is to change that line to read:

            if target is not None and int(target) == self.domid :

I have patched all of my existing Xen installs, and tested the fix. This might
make a good candidate for inclusion in 4.0.1, as well as xen-unstable (if it has
the same piece of code).

-John Weekes

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On Fri, May 14, 2010 at 03:02:04PM -0700, John Weekes
wrote:
>    I''m running Xen 4.0.1-rc1-pre (21122:7d1d4abd8b44). In this
version, and
>    in all other Xen 3.5-unstable + versions that I''ve looked at,
is
>    this function in XendDomainInfo.py:
>        def getStubdomDomid(self):
>            dom_list = xstransact.List(''/local/domain'')
>            for d in dom_list:
>                target = xstransact.Read(''/local/domain/''
+ d + ''/target'')
>                if target is not None and int(target) is self.domid :
>                    return int(d)
>            return None
>    The bolded line has a bug in it, unfortunately. This function is used in
>    domain destruction, and destruction works properly when a domain has a
>    stubdom, but only until it reaches a domid of around 257. Past that, it
>    breaks. This can be easily seen by simply starting a bunch of HVMs with
>    stubdoms (I tested by creating + destroying the same one, over and
over).
> 
>    What''s interesting is that the function works at all --
"is" really does
>    not seem to be the right comparator to use here.
> 
>    The fix is to change that line to read:
>                if target is not None and int(target) == self.domid :
>    I have patched all of my existing Xen installs, and tested the fix. This
>    might make a good candidate for inclusion in 4.0.1, as well as
>    xen-unstable (if it has the same piece of code).
> 
You might want to submit an actual patch together with a Signed-off-by line.
See the end of: http://wiki.xensource.com/xenwiki/XenFaq

-- Pasi


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> You might want to submit an actual patch
I could work on this further next week. My hope was that someone with the 
build setup already configured for both versions could create one in just a 
few seconds, though.
> together with a Signed-off-by line.
Not needed in this case.

-John 


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