Re: [Qemu-block] [Qemu-devel] [RFC PATCH 28/56] block: Widen dirty bitmap granularity to uint64_t for safety
On 08/07/2017 08:55 PM, John Snow wrote: > > > On 08/07/2017 10:45 AM, Markus Armbruster wrote: >> Block dirty bitmaps represent granularity in bytes as uint32_t. It >> must be a power of two and a multiple of BDRV_SECTOR_SIZE. >> >> The trouble with uint32_t is computations like this one in >> mirror_do_read(): >> >> uint64_t max_bytes; >> >> max_bytes = s->granularity * s->max_iov; >> >> The operands of * are uint32_t and int, so the product is computed in >> uint32_t (assuming 32 bit int), then zero-extended to uint64_t. >> >> Since granularity is generally combined with 64 bit file offsets, it's >> best to make it 64 bits, too. Less opportunity to screw up. And definitely conflicts with my work on byte-based block status. >> >> -uint32_t bdrv_dirty_bitmap_meta_granularity(BdrvDirtyBitmap *bitmap) >> -{ >> -return BDRV_SECTOR_SIZE << hbitmap_granularity(bitmap->meta); >> -} > > Why? Unused? Not cool enough to mention? Already deleted as unused in my byte-based series. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org signature.asc Description: OpenPGP digital signature
Re: [Qemu-block] [Qemu-devel] [RFC PATCH 28/56] block: Widen dirty bitmap granularity to uint64_t for safety
On 08/07/2017 10:45 AM, Markus Armbruster wrote: > Block dirty bitmaps represent granularity in bytes as uint32_t. It > must be a power of two and a multiple of BDRV_SECTOR_SIZE. > > The trouble with uint32_t is computations like this one in > mirror_do_read(): > > uint64_t max_bytes; > > max_bytes = s->granularity * s->max_iov; > > The operands of * are uint32_t and int, so the product is computed in > uint32_t (assuming 32 bit int), then zero-extended to uint64_t. > > Since granularity is generally combined with 64 bit file offsets, it's > best to make it 64 bits, too. Less opportunity to screw up. > > Signed-off-by: Markus Armbruster[bweeooop] > --- a/block/dirty-bitmap.c > +++ b/block/dirty-bitmap.c [bwp] > @@ -506,16 +506,11 @@ uint32_t > bdrv_get_default_bitmap_granularity(BlockDriverState *bs) > return granularity; > } > > -uint32_t bdrv_dirty_bitmap_granularity(const BdrvDirtyBitmap *bitmap) > +uint64_t bdrv_dirty_bitmap_granularity(const BdrvDirtyBitmap *bitmap) > { > return BDRV_SECTOR_SIZE << hbitmap_granularity(bitmap->bitmap); > } > > -uint32_t bdrv_dirty_bitmap_meta_granularity(BdrvDirtyBitmap *bitmap) > -{ > -return BDRV_SECTOR_SIZE << hbitmap_granularity(bitmap->meta); > -} Why? Unused? Not cool enough to mention?