Re: [Qemu-devel] Re: [libvirt] Re: [PATCH 2/3] Introduce monitor 'wait' command

[Anthony Liguori <anthony@codemonkey.ws>]

Hollis Blanchard wrote:
> On Wed, 2009-04-08 at 14:35 -0500, Anthony Liguori wrote:
>   
>> You're basically saying that if something isn't connected, drop them.  
>> If it is connected, do a monitor_printf() such that you're never queuing 
>> events.  Entirely reasonable and I've considered it.
>>
>> However, I do like the idea though of QEMU queuing events for a certain 
>> period of time.  Not everyone always has something connected to a 
>> monitor.  I may notice that my NFS server (which runs in a VM) is not 
>> responding, VNC to the system, switch to the monitor, and take a look at 
>> the event log.  If I can get the past 10 minutes of events, I may see 
>> something useful like a host IO failure.
>>     
>
> "10 minutes" is the red flag for me. Why not 5 minutes? 60 minutes? 24
> hours? The fact that it's so arbitrary suggests it doesn't really
> belong. If you care, you can attach a logging daemon that keeps the last
> 10 minutes worth of data...
>   

It has to be some finite amount.   You're right, it's arbitrary, but so 
is every other memory limitation we have in QEMU.  You could make it 
user configurable but that's just punting the problem.

You have to do some level of buffering.  It's unavoidable.  If you 
aren't buffering at the event level, you buffer at the socket level, etc.

Regards,

Anthony Liguori