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

[John Snow]

On 05/19/2017 07:02 PM, John Snow wrote:
> 
> 
> 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 <address@hidden>
>> ---
>>  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.
> 

I must have been *REALLY* tired when I sent this; I had thought you were
replacing an assertion instead of just adding one.

I'm sorry about that.

>>      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
>>