Re: [Qemu-devel] [Qemu-stable] [PATCH 1/2] block: Fix unaligned zero write

[Peter Lieven <pl@kamp.de>]

Am 23.03.2015 um 15:14 schrieb Stefan Hajnoczi:
> On Mon, Mar 23, 2015 at 12:46:09PM +0800, Fam Zheng wrote:
>> @@ -3435,6 +3446,10 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
>>           bytes = ROUND_UP(bytes, align);
>>       }
>>   
>> +    if (use_local_qiov) {
>> +        /* Local buffer may have non-zero data. */
>> +        flags &= ~BDRV_REQ_ZERO_WRITE;
>> +    }
>>       ret = bdrv_aligned_pwritev(bs, &req, offset, bytes,
>>                                  use_local_qiov ? &local_qiov : qiov,
>>                                  flags);
>> @@ -3475,14 +3490,32 @@ int coroutine_fn bdrv_co_write_zeroes(BlockDriverState *bs,
>>                                         int64_t sector_num, int nb_sectors,
>>                                         BdrvRequestFlags flags)
>>   {
>> +    int ret;
>> +
>>       trace_bdrv_co_write_zeroes(bs, sector_num, nb_sectors, flags);
>>   
>> -    if (!(bs->open_flags & BDRV_O_UNMAP)) {
>> -        flags &= ~BDRV_REQ_MAY_UNMAP;
>> -    }
> Why is it okay to drop this when the request is aligned?

I also think it is not. This is the only point in the code that clears the
MAY_UNMAP flag when we do not open with discard=on

Peter