Re: [Qemu-devel] Re: KVM call agenda for Apr 27

[Kevin Wolf <kwolf@redhat.com>]

Am 27.04.2010 00:36, schrieb Anthony Liguori:
> On 04/26/2010 05:12 PM, Chris Wright wrote:
>> * Anthony Liguori (anthony@codemonkey.ws) wrote:
>>    
>>> On 04/26/2010 12:26 PM, Chris Wright wrote:
>>>      
>>>> Please send in any agenda items you are interested in covering.
>>>>
>>>> While I don't expect it to be the case this week, if we have a
>>>> lack of agenda items I'll cancel the week's call.
>>>>        
>>> - qemu management interface (and libvirt)
>>> - stable tree policy (push vs. pull and call for stable volunteers)
>>>      
>> block plug in (follow-on from qmp block watermark)
>>    
> 
> A few comments:
> 
> 1) The problem was not block watermark itself but generating a 
> notification on the watermark threshold.  It's a heuristic and should be 
> implemented based on polling block stats.  Otherwise, we'll be adding 
> tons of events to qemu that we'll struggle to maintain.

Polling just feels completely wrong. You're almost guaranteed to poll in
the wrong intervals because depending on what the guest is doing you
might need it every couple of seconds (installation) or you may not need
it in days (just working on a fully allocated image).

> 2) A block plugin doesn't solve the problem if it's just at the 
> BlockDriverState level because it can't interact with qcow2.

There's no interaction with qcow2 needed, it would just need to remember
the highest offset it was requested to read or write. But I'd really
hate to stick another protocol between qcow2 and file.

It doesn't solve the problem nicely though because it still needs to
generate some event which is not present in a normal qemu without the
plugin.

Kevin