On 22.02.2016 17:31, Eric Blake wrote:
> 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.Can do, will do, thanks. Max
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