Re: [Qemu-block] [PATCH 1/1] block: ignore flush requests when storage is clean

[Kevin Wolf]

Am 21.06.2016 um 09:32 hat Paolo Bonzini geschrieben:
> 
> 
> On 20/06/2016 17:19, Denis V. Lunev wrote:
> > +    /* Check if storage is actually dirty before flushing to disk */
> > +    if (!bs->dirty) {
> > +        goto flush_parent;
> > +    }
> > +    bs->dirty = false;
> > +
> 
> This should be cleared after the flush is complete.  If you have
> 
>     write begin
>     write end
>     flush #1 begin
>     flush #2 begin
> 
> Then the second flush must only return after the first has finished.

I think clearing bs->dirty after the flush completion wouldn't
necessarily be right either if there are concurrent writes in flight, as
only completed writes are guaranteed to be flushed by it.

Kevin