On 02/20/2016 10:39 AM, Max Reitz wrote:
> Currently, we do not define exactly what is returned when read, but
> having a reliable source of zeros is always nice.
>
> Signed-off-by: Max Reitz <mre...@redhat.com>
> ---
> block/null.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/block/null.c b/block/null.c
> index d90165d..ad883d9 100644
> --- a/block/null.c
> +++ b/block/null.c
> @@ -90,6 +90,7 @@ static coroutine_fn int null_co_readv(BlockDriverState *bs,
> int64_t sector_num, int nb_sectors,
> QEMUIOVector *qiov)
> {
> + qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
> return null_co_common(bs);
> }Shouldn't this be made optional? That is, one of the points of null-co was to be as fast as possible, and the memset will slow us down. So having an optional bool as part of the null-co setup, which defaults off for back-compat but can be turned on for guaranteed all-zero reads, sounds like it would be nicer than forcing all-zero reads. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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