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Re: [Qemu-devel] [PATCH V4 10/16] qmp event: Add COLO_EXIT event to noti

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH V4 10/16] qmp event: Add COLO_EXIT event to notify users while exited COLO
Date: Tue, 6 Feb 2018 09:20:17 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

On 02/05/2018 09:13 PM, Zhang Chen wrote:

+{ '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 <address@hidden>
any idea about this?

Nothing to add, Markus is right - implementing a new mechanism that logs all events as they are issued, and teaching libvirt to parse that log at startup, is more work than just implementing a query-foo command that libvirt already knows how to use to query current state on first connect (and based on that query, make an intelligent decision on whether at least one event was missed during downtime). So far, no one has come up with an event that is so important it must be logged, when compared to the working alternative of just having events be ways to optimize performance so that the query- command doesn't have to be polled all the time, but no severe loss if the event is missed because the query- can be used in its place.

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

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