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Re: [Qemu-devel] Signal handling and qcow2 image corruption

From: Avi Kivity
Subject: Re: [Qemu-devel] Signal handling and qcow2 image corruption
Date: Thu, 06 Mar 2008 08:57:22 +0200
User-agent: Thunderbird (X11/20080226)

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 

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