[Libguestfs] [p2v PATCH 09/10] rely on Linux for killing nbdkit, when the parent thread exits

[Richard W.M. Jones]

So this patch unfortunately isn't correct for a few reasons:

(1) Non-Linux/BSD OSes don't support a concept like
--exit-with-parent.  nbdkit will exit with an error if you try to use
this feature on such OSes.  You can test if --exit-with-parent is
supported before trying to use it by:

  nbdkit --exit-with-parent --version

which will exit with an error if the feature is not supported.

However this isn't really a major issue for us.  The bigger one is:

(2) --exit-with-parent is not reliable.  It's best thought of as a
best-effort, fallback attempt to kill nbdkit.  It requires that nbdkit
issues a prctl(2), so any time that the parent (virt-p2v) dies before
nbdkit issues the prctl, nbdkit will not get cleaned up.

So I would say to implement this you'll have to:

 - Check if “system ("nbdkit --exit-with-parent --version")” returns 0.

 - If so, add the --exit-with-parent flag (otherwise, don't).

 - Keep the PID tracking / kill code that already exists.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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