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

[Avi Kivity]

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.