Re: [Qemu-devel] [PATCH v7 3/3] qmp.c: system_wakeup: runstate and wake-up support check

[Markus Armbruster <armbru@redhat.com>]

This affects both QMP and HMP.  Let's rephrase the title to

    qmp hmp: Make system_wakeup check wake-up support and run state

Can do that in my tree.

Daniel Henrique Barboza <danielhb@linux.ibm.com> writes:

> The qmp/hmp command 'system_wakeup' is simply a direct call to
> 'qemu_system_wakeup_request' from vl.c. This function verifies if
> runstate is SUSPENDED and if the wake up reason is valid before
> proceeding. However, no error or warning is thrown if any of those
> pre-requirements isn't met. There is no way for the caller to
> differentiate between a successful wakeup or an error state caused
> when trying to wake up a guest that wasn't suspended.
>
> This means that system_wakeup is silently failing, which can be
> considered a bug. Adding error handling isn't an API break in this
> case - applications that didn't check the result will remain broken,
> the ones that check it will have a chance to deal with it.
>
> Adding to that, recent changes in query-target added a new flag called

"... the commit before previous extended query-target with a new flag..."

> wakeup-suspend-support that indicates if the guest has the capability
> of waking up from suspended state. Although such guest will never
> reach SUSPENDED state and erroring it out in this scenario would
> suffice, it is more informative for the user to differentiate between a
> failure because the guest isn't suspended versus a failure because the
> guest does not have support for wake up at all.
>
> All this considered, this patch changes qmp_system_wakeup to:
>
> - check if the guest has the capability to wake-up from suspend. If
> not, error out informing about the lack of support;
>
> - make the runstate verification before proceeding to call
> qemu_system_wakeup_request, firing up an error message if the user tries
> to wake up a machine that isn't in SUSPENDED state.
>
> After this patch, this is the output of system_wakeup in a guest that
> does not have wake-up from suspend support (ppc64):
>
> (qemu) system_wakeup
> wake-up from suspend is not supported by this guest
> (qemu)
>
> And this is the output of system_wakeup in a x86 guest that has the
> support but isn't suspended:
>
> (qemu) system_wakeup
> Unable to wake up: guest is not in suspended state
> (qemu)

The examples are a nice touch.

> Reported-by: Balamuruhan S <bala24@linux.vnet.ibm.com>
> Signed-off-by: Daniel Henrique Barboza <danielhb@linux.ibm.com>
> ---
>  hmp.c          |  4 +++-
>  qapi/misc.json |  3 ++-
>  qmp.c          | 10 ++++++++++
>  3 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/hmp.c b/hmp.c
> index ef93f4878b..d177d14cc9 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -1156,7 +1156,9 @@ void hmp_cont(Monitor *mon, const QDict *qdict)
>  
>  void hmp_system_wakeup(Monitor *mon, const QDict *qdict)
>  {
> -    qmp_system_wakeup(NULL);
> +    Error *err = NULL;

Blank line between declaration and statement, please.  Happy to touch
this up in my tree.

> +    qmp_system_wakeup(&err);
> +    hmp_handle_error(mon, &err);
>  }
>  
>  void hmp_nmi(Monitor *mon, const QDict *qdict)
> diff --git a/qapi/misc.json b/qapi/misc.json
> index efba0449a6..73bfc3e436 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -1247,7 +1247,8 @@
>  #
>  # If the guest has wake-up from suspend support enabled
>  # (wakeup-suspend-support flag from query-target), wakeup guest from
> -# suspend. Does nothing otherwise.
> +# suspend if the guest is in SUSPENDED state. Returns an error
> +# otherwise.
>  #
>  # Since:  1.1
>  #
> diff --git a/qmp.c b/qmp.c
> index 25fdc9a5b2..5366e963ad 100644
> --- a/qmp.c
> +++ b/qmp.c
> @@ -205,6 +205,16 @@ void qmp_cont(Error **errp)
>  
>  void qmp_system_wakeup(Error **errp)
>  {
> +    if (!qemu_wakeup_suspend_support()) {
> +        error_setg(errp,
> +                   "wake-up from suspend is not supported by this guest");
> +        return;
> +    }
> +    if (!runstate_check(RUN_STATE_SUSPENDED)) {
> +        error_setg(errp,
> +                   "Unable to wake up: guest is not in suspended state");
> +        return;
> +    }
>      qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
>  }