[libvirt] Re: [Qemu-devel] [PATCH 1/6] Allow multiple monitor devices (v2)

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Avi Kivity wrote:
 hotplug disk
 -ENOSPC on disk

It's true that events don't correlate directly to commands, but they do correlate to the state of the system and that is affected by commands.
events are time stamped.  In non-human mode, I think command responses 
should be time stamped too so that a management tool knows when the 
event was generated and can correlate the system state to the particular 
event.
Sure, we'll need to make sure notifications don't mix with command responses, and that all commands are acked (the (qemu) prompt serves that purpose now), but it seems to me do be a lot easier for the management end.
FWIW, you can have asynchronous completion of monitor commands.  See 
migration as an example.  The (qemu) prompt is the ack that the 
command is finished.  You can only have one async command per monitor 
session which is why you need multiple monitors.
Migration has the -d switch to be truly async (not to wait).  We need 
an async notifier to tell us migration has finished or failed.
Multiplexing multiple monitor sessions AFAICT is going to require a 
non-human mode.  But it's totally orthogonal to this patch set.  You 
could implement it today if you wanted.
If we had a non-human monitor mode, I think it would be fine to have 
many monitors multiplexed over a single channel.  The internal 
monitor abstraction doesn't change.
I don't understand why we need to multiplex many monitors over one 
channel.  Let's keep one monitor, but with the ability to send 
notifications to the other end.
I don't understand how you think it would be implemented.  Each command 
is going to have a unique 'Monitor *' associated with it.  How that ends 
up being displayed to the user/management tool is irrelevant.  Right 
now, you can only have one 'Monitor *' active on a single "channel" at a 
time.  This is mostly a matter of output format.  I don't see how we can 
keep the monitor output consistent and compatible as it stands today and 
still support multiple 'Monitor *'s active in a single channel.
--
Regards,

Anthony Liguori

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