| Managed start up options |
| ======================== |
| |
| In system mode emulation, it's possible to create a VM in a paused |
| state using the ``-S`` command line option. In this state the machine |
| is completely initialized according to command line options and ready |
| to execute VM code but VCPU threads are not executing any code. The VM |
| state in this paused state depends on the way QEMU was started. It |
| could be in: |
| |
| - initial state (after reset/power on state) |
| - with direct kernel loading, the initial state could be amended to execute |
| code loaded by QEMU in the VM's RAM and with incoming migration |
| - with incoming migration, initial state will be amended with the migrated |
| machine state after migration completes |
| |
| This paused state is typically used by users to query machine state and/or |
| additionally configure the machine (by hotplugging devices) in runtime before |
| allowing VM code to run. |
| |
| However, at the ``-S`` pause point, it's impossible to configure options |
| that affect initial VM creation (like: ``-smp``/``-m``/``-numa`` ...) or |
| cold plug devices. The experimental ``--preconfig`` command line option |
| allows pausing QEMU before the initial VM creation, in a "preconfig" state, |
| where additional queries and configuration can be performed via QMP |
| before moving on to the resulting configuration startup. In the |
| preconfig state, QEMU only allows a limited set of commands over the |
| QMP monitor, where the commands do not depend on an initialized |
| machine, including but not limited to: |
| |
| - ``qmp_capabilities`` |
| - ``query-qmp-schema`` |
| - ``query-commands`` |
| - ``query-status`` |
| - ``x-exit-preconfig`` |
