Re: [Qemu-devel] Live migration using qcow2

[Dietmar Maurer]

> On Thu, Feb 21, 2013 at 12:02:18PM +0000, Dietmar Maurer wrote:
> > > The problem is about cache coherency. Local files work just fine
> > > with cache=writeback, but if you migrate to a different host, you
> > > get the problem that the destination kernel may cache some parts of
> > > the image while the source is still writing to it. When you do the
> > > actual switch to the destination host and the backend doesn't take
> > > care of invalidating that cache, you might (partially) read outdated data.
> >
> > Isn't there a way to force a cache flush?
> 
> Forcing the caches for a single file to be dropped? Not that I'm aware of (or
> anyone else who looked into the problem before we decided to document
> cache=none as a requirement).

What happens if you open a file with O_DIRECT first, the reopen with other 
flags? 
Would that flush the cache?