Re: [Qemu-devel] [PATCH v3] block: mirror - fix full sync mode when target does not support zero init

[Jeff Cody <jcody@redhat.com>]

On Thu, Oct 01, 2015 at 03:35:15PM +0200, Paolo Bonzini wrote:
> 
> 
> On 01/10/2015 15:14, Jeff Cody wrote:
> > During mirror, if the target device does not support zero init, a
> > mirror may result in a corrupted image for sync="full" mode.
> > 
> > This is due to how the initial dirty bitmap is set up prior to copying
> > data - we did not mark sectors as dirty that are unallocated.  This
> > means those unallocated sectors are skipped over on the target, and for
> > a device without zero init, invalid data may reside in those holes.
> > 
> > If both of the following conditions are true, then we will explicitly
> > mark all sectors as dirty:
> > 
> >     1.) sync = "full"
> >     2.) bdrv_has_zero_init(target) == false
> > 
> > If the target does support zero init, but a target image is passed in
> > with data already present (i.e. an "existing" image), it is assumed the
> > data present in the existing image is valid data for those sectors.
> > 
> > Signed-off-by: Jeff Cody <jcody@redhat.com>
> > ---
> >  block/mirror.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/block/mirror.c b/block/mirror.c
> > index a258926..ce367e0 100644
> > --- a/block/mirror.c
> > +++ b/block/mirror.c
> > @@ -455,6 +455,8 @@ static void coroutine_fn mirror_run(void *opaque)
> >      if (!s->is_none_mode) {
> >          /* First part, loop on the sectors and initialize the dirty bitmap.  */
> >          BlockDriverState *base = s->base;
> > +        bool mark_all_dirty = s->base == NULL && !bdrv_has_zero_init(s->target);
> > +
> >          for (sector_num = 0; sector_num < end; ) {
> >              /* Just to make sure we are not exceeding int limit. */
> >              int nb_sectors = MIN(INT_MAX >> BDRV_SECTOR_BITS,
> > @@ -477,7 +479,7 @@ static void coroutine_fn mirror_run(void *opaque)
> >              }
> >  
> >              assert(n > 0);
> > -            if (ret == 1) {
> > +            if (ret == 1 || mark_all_dirty) {
> >                  bdrv_set_dirty_bitmap(s->dirty_bitmap, sector_num, n);
> >              }
> >              sector_num += n;
> > @@ -767,8 +769,8 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
> >      base = mode == MIRROR_SYNC_MODE_TOP ? bs->backing_hd : NULL;
> >      mirror_start_job(bs, target, replaces,
> >                       speed, granularity, buf_size,
> > -                     on_source_error, on_target_error, unmap, cb, opaque, errp,
> > -                     &mirror_job_driver, is_none_mode, base);
> > +                     on_source_error, on_target_error, unmap,
> > +                     cb, opaque, errp, &mirror_job_driver, is_none_mode, base);
> >  }
> >  
> >  void commit_active_start(BlockDriverState *bs, BlockDriverState *base,
> > 
> 
> Unnecessary last hunk, but the patch is good anyway.
> 
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks,

I'll go ahead and drop the last hunk when applying.

Jeff