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

[Paolo Bonzini <pbonzini@redhat.com>]

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>