Re: [Xen-tools] Re: [PATCH] Make xend reject duplicates and rename zombies

[Anthony Liguori <aliguori@us.ibm.com>]

Christian Limpach wrote:

>On 9/15/05, Anthony Liguori <aliguori@us.ibm.com> wrote:
>  
>
>>I think this is not the right solution to the problem at hand.  The
>>problem stems from the fact that xm destroy is just a call to
>>xc_domain_destroy which is really just a request to the hypervisor to
>>destroy the domain.
>>    
>>
>
>Indeed.
>
>  
>
>>Therefore, there is a race condition if you assume that the domain is
>>dead after xm destroy returns.  This patch renames the domain name which
>>prevents a name class but does not solve the general problem.  Consider,
>>for instance, if a domain is using a block device and you do an xm
>>destroy.  It is not safe to create a new domain with that same block
>>device until you know that the previously mentioned domain is gone.
>>    
>>
>
>I think renaming would make sense if a domain is crashed.  You might
>want to keep the domain around to attach a debugger to it but at the
>same time restart a fresh copy as soon as possible.
>  
>
As long as you can make sure to rename *after* all of the devices have 
been properly torn down.

Otherwise, we need to make sure to make it well known that restarting a 
domain after a crash can result in very bad things :-)

Regards,

Anthony Liguori

>>This patch would allow:
>>xm destroy xmexample1 && xm create /etc/xen/xmexample1
>>
>>I think the right solution is to make xm destroy not return until the
>>domain has actually gone away and add a flag to xm destroy to return
>>immediately if that behavior is ever desired.
>>    
>>
>
>Sounds good.
>
>  
>
>>I'll work up a patch tonight after class.
>>    
>>
>
>Thanks!
>
>     christian
>
>  
>