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

[Paolo Bonzini]

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.

Paolo