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

To: Christian.Limpach@xxxxxxxxxxxx
Subject: Re: [Xen-tools] Re: [Xen-devel] [PATCH] Make xend reject duplicates and rename zombies
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Fri, 16 Sep 2005 16:37:23 -0500
Cc: Xen Tools Developers <xen-tools@xxxxxxxxxxxxxxxxxxx>, Xen Developers <xen-devel@xxxxxxxxxxxxxxxxxxx>
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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.


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 :-)


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.



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