Re: [Qemu-devel] [PATCH V4 10/16] qmp event: Add COLO_EXIT event to notify users while exited COLO

[Zhang Chen <zhangckid@gmail.com>]

On Tue, Feb 6, 2018 at 3:27 PM, Markus Armbruster <armbru@redhat.com> wrote:

> Zhang Chen <zhangckid@gmail.com> writes:
>
> > On Sat, Feb 3, 2018 at 3:49 PM, Markus Armbruster <armbru@redhat.com>
> wrote:
> >
> >> Zhang Chen <zhangckid@gmail.com> writes:
> >>
> >> > From: zhanghailiang <zhang.zhanghailiang@huawei.com>
> >> >
> >> > If some errors happen during VM's COLO FT stage, it's important to
> >> > notify the users of this event. Together with 'x-colo-lost-heartbeat',
> >> > Users can intervene in COLO's failover work immediately.
> >> > If users don't want to get involved in COLO's failover verdict,
> >> > it is still necessary to notify users that we exited COLO mode.
> >> >
> >> > Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> >> > Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> >> > Signed-off-by: Zhang Chen <zhangckid@gmail.com>
> >> > Reviewed-by: Eric Blake <eblake@redhat.com>
> >> [...]
> >> > diff --git a/qapi/migration.json b/qapi/migration.json
> >> > index 70e7b67..6fc95b7 100644
> >> > --- a/qapi/migration.json
> >> > +++ b/qapi/migration.json
> >> > @@ -869,6 +869,41 @@
> >> >    'data': [ 'none', 'require', 'active', 'completed', 'relaunch' ] }
> >> >
> >> >  ##
> >> > +# @COLO_EXIT:
> >> > +#
> >> > +# Emitted when VM finishes COLO mode due to some errors happening or
> >> > +# at the request of users.
> >> > +#
> >> > +# @mode: which COLO mode the VM was in when it exited.
> >> > +#
> >> > +# @reason: describes the reason for the COLO exit.
> >> > +#
> >> > +# Since: 2.12
> >> > +#
> >> > +# Example:
> >> > +#
> >> > +# <- { "timestamp": {"seconds": 2032141960, "microseconds": 417172},
> >> > +#      "event": "COLO_EXIT", "data": {"mode": "primary", "reason":
> "request" } }
> >> > +#
> >> > +##
> >> > +{ 'event': 'COLO_EXIT',
> >> > +  'data': {'mode': 'COLOMode', 'reason': 'COLOExitReason' } }
> >>
> >> Standard question when I see a new event: is there a way to poll for the
> >> event's information?  If not, why don't we need one?
> >>
> >>
> > Your means is we'd better print the information to a log file or
> something
> > like that for all qemu events?
> > CC  Eric Blake <eblake@redhat.com>
> > any idea about this?
>
> Events carrying state change information management applications want to
> track are generally paired with a query- command.  While the management
> application is connected, it can track by passively listening for state
> change events.  After (re)connect, it has to actively query the current
> state.
>
> Questions?
>


If I understand correctly, maybe we need a qemu events general history
mechanism
to solve this problem,
because lots of qemu events can't resend the current state. Yes, when the
"management application"(like libvirt)
lose the connection to qemu,  management application can't get the
information after reconnect.

Thanks
Zhang Chen


>
> >> Remember, management applications might miss events when they lose the
> >> connection and have to reconnect, say because the management application
> >> needs to be restarted.
> >>
> >> > +
> >> > +##
> >> > +# @COLOExitReason:
> >> > +#
> >> > +# The reason for a COLO exit
> >> > +#
> >> > +# @request: COLO exit is due to an external request
> >> > +#
> >> > +# @error: COLO exit is due to an internal error
> >> > +#
> >> > +# Since: 2.12
> >> > +##
> >> > +{ 'enum': 'COLOExitReason',
> >> > +  'data': [ 'request', 'error' ] }
> >> > +
> >> > +##
> >> >  # @x-colo-lost-heartbeat:
> >> >  #
> >> >  # Tell qemu that heartbeat is lost, request it to do takeover
> procedures.
>