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Date: Fri, 02 May 2008 09:32:35 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: [Qemu-devel] Re: [kvm-devel] Feedback and errors
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To: Avi Kivity <avi@qumranet.com>
Cc: nadim khemir <nadim@khemir.net>, kvm-devel@lists.sourceforge.net, qemu-devel@nongnu.org

Avi Kivity wrote:
> nadim khemir wrote:
>   
>> Hi, great work.
>>
>> While playing with kvm-qemu I noticed a few points that might be of interrest:
>>
>> 1/ -loadvm and -snapshot don't work together. It works as if -loadvm wasn't 
>> passed as argument
>>
>> 2/ two instances of kvm can be passed the same -hda. There is no locking 
>> whatsoever. This messes up things seriously.
>>
>>   
>>     
>
> These two are upstream qemu problems. Copying qemu-devel.
>
> I guess using file locking by default would improve the situation, and 
> we can add a -drive ...,exclusive=no option for people playing with 
> cluster filesystems.
>   

This is not a situation where the user has a reasonable expectation of 
what will happen that we violate.  If the user is unhappy with the 
results, it's because the user made a mistake.  FWIW, the whole override 
thing for Xen has been an endless source of pain.  It's very difficult 
(if not impossible) to accurately determine if someone else is using the 
disk.  Also, it tends to confuse people trying to do something 
legitimate more often than helping someone doing something stupid.

I very frequently run multiple VMs with the same disk.  I do it strictly 
for the purposes of benchmarking.  There are ways to share a disk 
without using a clustered filesystem.

If a higher level management tool wants to enforce a policy (like 
libvirt), then let it.  We should not be enforcing policies within QEMU 
though.

Regards,

Anthony Liguori