Re: [Qemu-devel] [PATCH 2/3] move vm stop/start to migrate_set_state

[Avi Kivity]

On 07/12/2009 10:10 PM, Anthony Liguori wrote:
> > It's actually a common scenario for block devices.  I don't know 
> > about networking, but for disks a write can be completed and then 
> > report an error if the cable or power was disconnected before the 
> > acknowledge could arrive.
>
>
> Is it common that a disk cable is yanked out before the ack arrives? 

It was common when I was doing filesystems.

> Are their gremlins in your servers :-)

Worse, QA.

> > It could conceivably happen with networking if the device reports an 
> > error when it isn't sure if the data was sent out or not (but it 
> > actually was), or if some path after the transmission required a 
> > memory allocation, which failed.
>
> But does this actually happen or is this all theoretical?

With block devices, my experience indicates that the probability of 
something happening is proportional to the damage it will cause.  With 
networking, it may be theoretical or practical, I suggest we don't rely 
on it either way.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.