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

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

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.

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.

This patch would allow:

xm destroy xmexample1 && xm create /etc/xen/xmexample1

Even though it might really be conflicting.  This could lead to *very* 
subtle device corruption down the road.

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.

I'll work up a patch tonight after class.

Regards,

Anthony Liguori

Dan Smith wrote:

>This patch is an update of my previous anti-duplicate-domain patch.
>Now, we check an existing same-name domain to see if it's in the
>"terminated" state, renaming it to "zombie-domid-name" if so.
>
>This basically makes the problem go away for me, as it gives the dying
>domain time to clean itself up.
>
>Test 10_create_fastdestroy from the next release of xm-test validates
>that this fixes the problem.
>
>Signed-off-by: Dan Smith <danms@us.ibm.com>
>
>  
>
>------------------------------------------------------------------------
>
>diff -r c27431cf81f9 tools/python/xen/xend/XendDomain.py
>--- a/tools/python/xen/xend/XendDomain.py	Thu Sep 15 13:17:24 2005
>+++ b/tools/python/xen/xend/XendDomain.py	Thu Sep 15 08:44:22 2005
>@@ -297,6 +297,20 @@
>         @param config: configuration
>         @return: domain
>         """
>+
>+        existing = self.domains.get_by_name(sxp.child_value(config, "name"))
>+        if existing:
>+            if existing.is_terminated():
>+                newname = "zombie-%i-%s" % (existing.domid, existing.name)
>+                log.debug("Renaming zombie domain %s -> %s" %
>+                          (existing.name, newname))
>+                existing.setName(newname)
>+            else:
>+                log.debug("Attempt to create duplicate domain %s" %
>+                          existing.name)
>+                raise XendError("Domain %s already exists as %i!" %
>+                                (existing.name, existing.id))
>+        
>         dominfo = XendDomainInfo.create(self.dbmap, config)
>         return dominfo
> 
>  
>
>------------------------------------------------------------------------
>
>
>  
>
>------------------------------------------------------------------------
>
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