Re: [Qemu-devel] [PATCH v12 1/2] mirror: Rewrite mirror_iteration

[Fam Zheng]

On Sat, 02/06 14:24, Max Reitz wrote:
> On 05.02.2016 03:00, Fam Zheng wrote:
> > The "pnum < nb_sectors" condition in deciding whether to actually copy
> > data is unnecessarily strict, and the qiov initialization is
> > unnecessarily for bdrv_aio_write_zeroes and bdrv_aio_discard.
> > 
> > Rewrite mirror_iteration to fix both flaws.
> > 
> > The output of iotests 109 is updated because we now report the offset
> > and len slightly differently in mirroring progress.
> > 
> > Signed-off-by: Fam Zheng <address@hidden>
> > ---
> >  block/mirror.c             | 335 
> > +++++++++++++++++++++++++++------------------
> >  tests/qemu-iotests/109.out |  80 +++++------
> >  trace-events               |   1 -
> >  3 files changed, 243 insertions(+), 173 deletions(-)
> > 
> > diff --git a/block/mirror.c b/block/mirror.c
> > index 2c0edfa..48cd0b3 100644
> > --- a/block/mirror.c
> > +++ b/block/mirror.c
> 
> [...]
> 
> > @@ -449,16 +520,16 @@ static void coroutine_fn mirror_run(void *opaque)
> >       */
> >      bdrv_get_backing_filename(s->target, backing_filename,
> >                                sizeof(backing_filename));
> > -    if (backing_filename[0] && !s->target->backing) {
> > -        ret = bdrv_get_info(s->target, &bdi);
> > -        if (ret < 0) {
> > -            goto immediate_exit;
> > -        }
> > -        if (s->granularity < bdi.cluster_size) {
> > -            s->buf_size = MAX(s->buf_size, bdi.cluster_size);
> > -            s->cow_bitmap = bitmap_new(length);
> > -        }
> > +    if (!bdrv_get_info(s->target, &bdi) && bdi.cluster_size) {
> 
> This should be bdi.has_cluster_size...

has_cluster_size is a member of ImageInfo not BlockDriverInfo, and is derived
from (bdi.cluster_size != 0).

> 
> > +        target_cluster_size = bdi.cluster_size;
> 
> ...and maybe we want an explicit minimum of BDRV_SECTOR_SIZE here; but I
> guess this is already assumed all over the block layer, so it may be
> fine without.

Okay, it doesn't hurt to add an assert here.

Fam

> 
> >      }
> > +    if (backing_filename[0] && !s->target->backing
> > +        && s->granularity < target_cluster_size) {
> > +        s->buf_size = MAX(s->buf_size, target_cluster_size);
> > +        s->cow_bitmap = bitmap_new(length);
> > +    }
> > +    s->target_cluster_sectors = target_cluster_size >> BDRV_SECTOR_BITS;
> 
> (this shouldn't be 0, so target_cluster_size needs to be at least
> BDRV_SECTOR_SIZE)
> 
> Max
>