Dejan Muhamedagic <[email protected]> writes:

> On Mon, Jun 03, 2013 at 06:19:06PM +0200, Ferenc Wagner wrote:
> 
>> I've got a script for resource creation, which puts the new resource in
>> a shadow CIB together with the necessary constraints, runs a simulation
>> and finally offers to commit the shadow CIB into the live config (by
>> invoking an interactive crm).  This works well.  My concern is that if
>> somebody else (another cluster administrator) changes anything in the
>> cluster configuration between creation of the shadow copy and the
>> commit, those changes will be silently reverted (lost) by the commit.
>> Is there any way to avoid the possibility of this?  According to
>> http://article.gmane.org/gmane.linux.highavailability.pacemaker/11021,
>> crm provides this functionality for its configure sessions [*], but the
>> shadow CIB route has good points as well (easier to script via cibadmin,
>> simulation), which I'd like to use.  Any ideas?
>
> Record the two epoch attributes of the cib tag at the beginning
> and check if they changed just before applying the changes.

Maybe I don't understand you right, but isn't this just narrowing the
time window of the race?  After all, that concurrent change can happen
between the epoch check and the commit, can't it?
-- 
Thanks,
Feri.
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