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Date: Thu, 06 Mar 2008 08:57:22 +0200
From: Avi Kivity <avi@qumranet.com>
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Subject: Re: [Qemu-devel] Signal handling and qcow2 image corruption
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To: qemu-devel@nongnu.org

Anthony Liguori wrote:
> David Barrett wrote:
>> I'm tracking down a image corruption issue and I'm curious if you can 
>> answer the following:
>>
>> 1) Is there any difference between sending a "TERM" signal to the 
>> QEMU process and typing "quit" at the monitor?
>
> Yes.  Since QEMU is single threaded, when you issue a quit, you know 
> you aren't in the middle of writing qcow2 meta data to disk.
>

That's not enough.  If you write a metadata pointer before allocating 
and writing the block, and you terminate between these two operations, 
the next write allocation will leave two pointers pointing to the same 
block.

I don't know if qemu is susceptible to this.



-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.