Re: [Xen-devel] Broken changing of config parameters for inactive domains

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Thu, Dec 07, 2006 at 06:09:11PM +0000, Daniel P. Berrange wrote:
> I've been testing out the inactive domain support in more depth, and looking
> for any odd interactions with xm and/or libvirt. In doing so I seem to have
> found some problems with changing the configuration of existing domains.
> 
> Since the config files are no longer in /etc/xen, users will no longer simply
> be able to edit them to tweak parameters before booting. Changing the files
> under /var/lib/xend/domains is not practical because XenD won't see the
> changed files (unless it uses Inotify - which it doesn't).
> 
> I don't think we need to worry about changing every single parameter at this
> time, but the basic set of memory, max memory, vcpu count should definitely
> be made to work with 'xm' / XMLRPC / SEXPR  apis.  If it was practical I'd
> also like to see the network & block device add/remove APIs work for inactive
> domains too.
> 
> 
> Currently, this sort of works, but results in very wierd bugs. eg changing
> the VCPUs for a guest:
> 
> So, I have a guest with 2 vcpus:
> 
>   # xm list
>   Name                                      ID   Mem VCPUs      State   
> Time(s)
>   Domain-0                                   0  2981     2     r-----   2381.2
>   demo                                           410     2                 0.0
> 
> 
> And want to change it to have 8:
> 
>   # xm set-vcpus demo 8
>   Command set-vcpus is deprecated.  Please use xm vcpu-set instead.
>   Error: 
>   Usage: xm <subcommand> [args]
>   [sniped rest of error]
> 
> So it apparently failed, but it actualy succeeded....
> 
>   # xm list
>   Name                                      ID   Mem VCPUs      State   
> Time(s)
>   Domain-0                                   0  2981     2     r-----   2381.7
>   demo                                           410     8                 0.0
> 
> What's even wierder, is if I now go and try to start the guest I end up
> with 2 copies of it !!
> 
>   # xm start demo
>   # xm list
>   Name                                      ID   Mem VCPUs      State   
> Time(s)
>   Domain-0                                   0  2981     2     r-----   2382.9
>   demo                                      45   410     8     -b----      0.8
>   demo                                      45   410     8     -b----      0.8

After a little more debugging, this duplicate domains problem seems to be
unrelated to the changing of config params.

I defined an inactive guest with a UUID of 
'66857c70-9898-fdfc-ed53-8eee3ba294bf'
which got stored on disk as 

  /var/lib/xend/domains/66857c70-9898-fdfc-ed53-8eee3ba294bf/config.sxp 

When starting the guest, however, it got a UUID of 
66857c709898fdfced538eee3ba294bf
so it thought there was a dup.  So, XenD needs to normalize UUIDs to remove any
embedded '-' when saving the inactive domain config to avoid this duplicate
domains issue.

Regards,
Dan.
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