Re: [Qemu-devel] [PATCH 09/25] block/dirty-bitmap: add readonly field to BdrvDirtyBitmap

[John Snow <jsnow@redhat.com>]

On 05/03/2017 08:25 AM, Vladimir Sementsov-Ogievskiy wrote:
> It will be needed in following commits for persistent bitmaps.
> If bitmap is loaded from read-only storage (and we can't mark it
> "in use" in this storage) corresponding BdrvDirtyBitmap should be
> read-only.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/dirty-bitmap.c         | 16 ++++++++++++++++
>  include/block/dirty-bitmap.h |  3 +++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
> index 90af37287f..ab6a95cf41 100644
> --- a/block/dirty-bitmap.c
> +++ b/block/dirty-bitmap.c
> @@ -44,6 +44,8 @@ struct BdrvDirtyBitmap {
>      int64_t size;               /* Size of the bitmap (Number of sectors) */
>      bool disabled;              /* Bitmap is read-only */
>      int active_iterators;       /* How many iterators are active */
> +    bool readonly;              /* Bitmap is read-only and may be changed only
> +                                   by deserialize* functions */
>      QLIST_ENTRY(BdrvDirtyBitmap) list;
>  };
>  
> @@ -436,6 +438,7 @@ void bdrv_set_dirty_bitmap(BdrvDirtyBitmap *bitmap,
>                             int64_t cur_sector, int64_t nr_sectors)
>  {
>      assert(bdrv_dirty_bitmap_enabled(bitmap));
> +    assert(!bdrv_dirty_bitmap_readonly(bitmap));

Doesn't this change the nature of the assertion?

We're going from
    return !(bitmap->disabled || bitmap->successor);
to
	!bitmap->readonly

That makes me a little nervous to ACK this patch, because the
correctness depends on how readonly is updated and manipulated in the
future, which makes it more prone to error.

>      hbitmap_set(bitmap->bitmap, cur_sector, nr_sectors);
>  }
>  
> @@ -443,12 +446,14 @@ void bdrv_reset_dirty_bitmap(BdrvDirtyBitmap *bitmap,
>                               int64_t cur_sector, int64_t nr_sectors)
>  {
>      assert(bdrv_dirty_bitmap_enabled(bitmap));
> +    assert(!bdrv_dirty_bitmap_readonly(bitmap));
>      hbitmap_reset(bitmap->bitmap, cur_sector, nr_sectors);
>  }
>  
>  void bdrv_clear_dirty_bitmap(BdrvDirtyBitmap *bitmap, HBitmap **out)
>  {
>      assert(bdrv_dirty_bitmap_enabled(bitmap));
> +    assert(!bdrv_dirty_bitmap_readonly(bitmap));
>      if (!out) {
>          hbitmap_reset_all(bitmap->bitmap);
>      } else {
> @@ -519,6 +524,7 @@ void bdrv_set_dirty(BlockDriverState *bs, int64_t cur_sector,
>          if (!bdrv_dirty_bitmap_enabled(bitmap)) {
>              continue;
>          }
> +        assert(!bdrv_dirty_bitmap_readonly(bitmap));
>          hbitmap_set(bitmap->bitmap, cur_sector, nr_sectors);
>      }
>  }
> @@ -540,3 +546,13 @@ int64_t bdrv_get_meta_dirty_count(BdrvDirtyBitmap *bitmap)
>  {
>      return hbitmap_count(bitmap->meta);
>  }
> +
> +bool bdrv_dirty_bitmap_readonly(const BdrvDirtyBitmap *bitmap)
> +{
> +    return bitmap->readonly;
> +}
> +
> +void bdrv_dirty_bitmap_set_readonly(BdrvDirtyBitmap *bitmap)
> +{
> +    bitmap->readonly = true;
> +}
> diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
> index 1e17729ac2..0aab5841f5 100644
> --- a/include/block/dirty-bitmap.h
> +++ b/include/block/dirty-bitmap.h
> @@ -75,4 +75,7 @@ void bdrv_dirty_bitmap_deserialize_ones(BdrvDirtyBitmap *bitmap,
>                                          bool finish);
>  void bdrv_dirty_bitmap_deserialize_finish(BdrvDirtyBitmap *bitmap);
>  
> +bool bdrv_dirty_bitmap_readonly(const BdrvDirtyBitmap *bitmap);
> +void bdrv_dirty_bitmap_set_readonly(BdrvDirtyBitmap *bitmap);
> +
>  #endif
>