[Qemu-devel] qcow2, lazy_refcounts and killing qemu

[Richard W.M. Jones]

I found out a few days ago that if you:

(1) Open a qcow2 file that has lazy_refcounts = on and a backing file, and

(2) Write lots of stuff, and

(3) Kill qemu with SIGTERM [which I believed, maybe incorrectly, is a
"nice" way to kill qemu]

.. then you can end up with a corrupt qcow2 file.  In particular the
qcow2 file sometimes forgot that it had a backing file, but I suspect
this was just a symptom and in fact the qcow2 file header wasn't being
written to disk correctly.

Is it correct that sending SIGTERM to qemu should kill it cleanly, or
is that no longer the case, or is lazy_refcounts a special case, or
have I found a bug?

I can reproduce this easily, although of course the reproducer will
involve libguestfs.

Rich.

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