[libvirt] [PATCHv4] qemu: allow blkstat/blkinfo calls during migration

[Paolo Bonzini]

On 05/21/2011 12:11 AM, Eric Blake wrote:
> I think we're safe.  It shouldn't matter if thread 2 reads thread 3's
> answer (because they are both read-only queries, and should be getting
> the same answer; or even if the answers differ, reading the newer answer
> is not horrible because it is still an accurate answer).

The queries could be for different disks, and one might fail.  The 
problem is mostly if the first fails and the second succeeds, and the 
program sees a success instead of a failure.

... but a much simpler fix is to make statRetCode a pointer, so that 
there is nothing to do on the producer side after the flag has been 
reset.  I strongly suggest doing this, as it is a very simple change 
that Cannot Make Things Worse (TM).

Paolo