Re: [Qemu-devel] [PATCH v7 07/11] cli: add --preconfig option

[Eric Blake]

On 05/04/2018 03:37 AM, Igor Mammedov wrote:
> This option allows pausing QEMU in the new RUN_STATE_PRECONFIG state,
> allowing the configuration of QEMU from QMP before the machine jumps
> into board initialization code of machine_run_board_init()
>
> The intent is to allow management to query machine state and additionally
> configure it using previous query results within one QEMU instance
> (i.e. eliminate the need to start QEMU twice, 1st to query board specific
> parameters and 2nd for actual VM start using query results for
> additional parameters).
>
> The new option complements -S option and could be used with or without
> it. The difference is that -S pauses QEMU when the machine is completely
> initialized with all devices wired up and ready to execute guest code
> (QEMU needs only to unpause VCPUs to let guest execute its code),
> while the "preconfig" option pauses QEMU early before board specific init
> callback (machine_run_board_init) is executed and allows the configuration
> of machine parameters which will be used by board init code.
>
> When early introspection/configuration is done, command 'exit-preconfig'
> should be used to exit RUN_STATE_PRECONFIG and transition to the next
> requested state (i.e. if -S is used then QEMU will pause the second
> time when board/device initialization is completed or start guest
> execution if -S isn't provided on CLI)
>
> PS:
> Initially 'preconfig' is planned to be used for configuring numa
> topology depending on board specified possible cpus layout.
>
> Signed-off-by: Igor Mammedov <address@hidden>
> ---

> +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. That's
> +when --preconfig command line option should be used. It allows pausing QEMU

s/when/when the/

> +before the initial VM creation, in a new 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:

Reviewed-by: Eric Blake <address@hidden>

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org