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

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Christian Limpach wrote:

> On 9/15/05, Anthony Liguori <aliguori@xxxxxxxxxx> 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
>
>  

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