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

[Vladimir Sementsov-Ogievskiy]

20.05.2017 02:02, 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.

Sorry for late answer, I was ill.

Hmm, old assert is still here. I just add another one. Readonly means: 
bitmap must not be changed by _get _set and _clear at all - from loading 
up to releasing. It is needed to maintain the case: "bitmap was loaded 
from read-only storage, so that it was not marked as 'in_use' in that 
storge". 'disabled' field is not appropriate because it is managed by user.

> >       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

--
Best regards,
Vladimir