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

[Fam Zheng]

On Mon, 03/23 14:14, Stefan Hajnoczi wrote:
> 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?

It's not. I will restore it.

> 
> > +    if (bdrv_req_is_aligned(bs, sector_num << BDRV_SECTOR_BITS,
> > +                            nb_sectors << BDRV_SECTOR_BITS)) {
> > +        ret = bdrv_co_do_writev(bs, sector_num, nb_sectors, NULL,
> > +                                BDRV_REQ_ZERO_WRITE | flags);
> > +    } else {