Libguestfs wants to use qemu to run a captive appliance. When the
program linked to libguestfs exits, we want qemu to be cleaned up.
Libguestfs goes to great lengths to do this at the moment: it either
forks a separate process to ensure clean-up is done, or it asks
libvirt to clean up the qemu process. However this is complicated and
not totally reliable.
On Linux, FreeBSD and macOS, there are mechanisms to ensure a signal
or message is delivered to a process when its parent process goes
away. The qemu test suite even uses this mechanism on Linux (see
PR_SET_PDEATHSIG in tests/qtest/libqtest.c).
In nbdkit we have long had the concept of running nbdkit captively,
and we have the nbdkit --exit-with-parent flag to help
(https://libguestfs.org/nbdkit-captive.1.html#EXIT-WITH-PARENT)
This commit adds the same mechanism. The syntax is:
qemu -run-with exit-with-parent=on [...]
This is not a feature that most typical users of qemu (for running
general purpose, long-lived VMs) should use, so it defaults to off.
The exit-with-parent.[ch] files are copied from nbdkit, where they
have a 3-clause BSD license which is compatible with qemu:
https://gitlab.com/nbdkit/nbdkit/-/tree/master/common/utils?ref_type=heads
Thanks: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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