Re: [Qemu-devel] [PATCH v2 7/8] block: core copy-on-read logic

[Stefan Hajnoczi]

On Wed, Nov 23, 2011 at 8:58 AM, Stefan Hajnoczi <address@hidden> wrote:
> On Wed, Nov 23, 2011 at 4:42 AM, Zhi Yong Wu <address@hidden> wrote:
>> On Thu, Nov 17, 2011 at 9:40 PM, Stefan Hajnoczi
>> <address@hidden> wrote:
>>> +    /* Cover entire cluster so no additional backing file I/O is required 
>>> when
>>> +     * allocating cluster in the image file.
>>> +     */
>>> +    round_to_clusters(bs, sector_num, nb_sectors,
>>> +                      &cluster_sector_num, &cluster_nb_sectors);
>> Why need to round down/up sector_num/nb_sectors in this function? The
>> detection of race condition for write request has been done before
>> this function.
>
> If we write less than a cluster then the image format will have to
> perform additional to populate the regions of the cluster that we did

"perform additional I/O"