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docs/microvm.rst: add instructions for shutting down the guest 

Add a new section explaining the particularities of the microvm
machine type for triggering a guest-initiated shut down.

Signed-off-by: Sergio Lopez <slp@redhat.com>
Message-Id: <20191115161338.42864-3-slp@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Sergio Lopez 2019-11-15 17:13:38 +01:00 committed by Paolo Bonzini
parent ff9d708933
commit 62e9dc3582
1 changed files with 21 additions and 0 deletions
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docs/microvm.rst
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@ -106,3 +106,24 @@ disabled::
-device virtio-blk-device,drive=test \
-netdev tap,id=tap0,script=no,downscript=no \
-device virtio-net-device,netdev=tap0
Triggering a guest-initiated shut down
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As the microvm machine type includes just a small set of system
devices, some x86 mechanisms for rebooting or shutting down the
system, like sending a key sequence to the keyboard or writing to an
ACPI register, doesn't have any effect in the VM.
The recommended way to trigger a guest-initiated shut down is by
generating a ``triple-fault``, which will cause the VM to initiate a
reboot. Additionally, if the ``-no-reboot`` argument is present in the
command line, QEMU will detect this event and terminate its own
execution gracefully.
Linux does support this mechanism, but by default will only be used
after other options have been tried and failed, causing the reboot to
be delayed by a small number of seconds. It's possible to instruct it
to try the triple-fault mechanism first, by adding ``reboot=t`` to the
kernel's command line.