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    qmp: query-current-machine with wakeup-suspend-support · 46ea94ca
    Daniel Henrique Barboza 提交于
    When issuing the qmp/hmp 'system_wakeup' command, what happens in a
    nutshell is:
    
    - qmp_system_wakeup_request set runstate to RUNNING, sets a wakeup_reason
    and notify the event
    - in the main_loop, all vcpus are paused, a system reset is issued, all
    subscribers of wakeup_notifiers receives a notification, vcpus are then
    resumed and the wake up QAPI event is fired
    
    Note that this procedure alone doesn't ensure that the guest will awake
    from SUSPENDED state - the subscribers of the wake up event must take
    action to resume the guest, otherwise the guest will simply reboot. At
    this moment, only the ACPI machines via acpi_pm1_cnt_init and xen_hvm_init
    have wake-up from suspend support.
    
    However, only the presence of 'system_wakeup' is required for QGA to
    support 'guest-suspend-ram' and 'guest-suspend-hybrid' at this moment.
    This means that the user/management will expect to suspend the guest using
    one of those suspend commands and then resume execution using system_wakeup,
    regardless of the support offered in system_wakeup in the first place.
    
    This patch creates a new API called query-current-machine [1], that holds
    a new flag called 'wakeup-suspend-support' that indicates if the guest
    supports wake up from suspend via system_wakeup. The machine is considered
    to implement wake-up support if a call to a new 'qemu_register_wakeup_support'
    is made during its init, as it is now being done inside acpi_pm1_cnt_init
    and xen_hvm_init. This allows for any other machine type to declare wake-up
    support regardless of ACPI state or wakeup_notifiers subscription, making easier
    for newer implementations that might have their own mechanisms in the future.
    
    This is the expected output of query-current-machine when running a x86
    guest:
    
    {"execute" : "query-current-machine"}
    {"return": {"wakeup-suspend-support": true}}
    
    Running the same x86 guest, but with the --no-acpi option:
    
    {"execute" : "query-current-machine"}
    {"return": {"wakeup-suspend-support": false}}
    
    This is the output when running a pseries guest:
    
    {"execute" : "query-current-machine"}
    {"return": {"wakeup-suspend-support": false}}
    
    With this extra tool, management can avoid situations where a guest
    that does not have proper suspend/wake capabilities ends up in
    inconsistent state (e.g.
    https://github.com/open-power-host-os/qemu/issues/31).
    
    [1] the decision of creating the query-current-machine API is based
    on discussions in the QEMU mailing list where it was decided that
    query-target wasn't a proper place to store the wake-up flag, neither
    was query-machines because this isn't a static property of the
    machine object. This new API can then be used to store other
    dynamic machine properties that are scattered around the code
    ATM. More info at:
    https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg04235.htmlReported-by: NBalamuruhan S <bala24@linux.vnet.ibm.com>
    Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>
    Message-Id: <20181205194701.17836-2-danielhb413@gmail.com>
    Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
    Acked-by: NEduardo Habkost <ehabkost@redhat.com>
    Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
    46ea94ca
xen-hvm.c 47.4 KB