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Re: [Qemu-devel] [RFC PATCH 28/56] block: Widen dirty bitmap granularity
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [RFC PATCH 28/56] block: Widen dirty bitmap granularity to uint64_t for safety |
Date: |
Tue, 08 Aug 2017 17:58:17 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux) |
John Snow <address@hidden> writes:
> 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 <address@hidden>
>
> [bweeooop]
>
>> --- a/block/dirty-bitmap.c
>> +++ b/block/dirty-bitmap.c
>
> [buuuuweeeep]
>
>> @@ -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?
I didn't feel like fixing an unused function, so I dropped it. Can
mention this in the commit message.
- Re: [Qemu-devel] [RFC PATCH 29/56] block: Make BlockDirtyInfo byte count unsigned in QAPI/QMP, (continued)
- [Qemu-devel] [RFC PATCH 43/56] blockjob: Lift speed sign conversion out of mirror_start(), Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 50/56] block: Make BLOCK_IMAGE_CORRUPTED offset, size unsigned in QAPI/QMP, Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 56/56] crypto: Make QCryptoBlockInfoLUKS offsets unsigned in QAPI/QMP, Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 42/56] blockjob: Lift speed sign conversion out of stream_start(), Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 28/56] block: Widen dirty bitmap granularity to uint64_t for safety, Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 20/56] block: Make ImageInfo sizes unsigned in QAPI/QMP, Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 38/56] blockjob: Lift speed sign conversion out of block_job_set_speed(), Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 27/56] block/dirty-bitmap: Clean up signed vs. unsigned dirty counts, Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 49/56] block: Make ImageCheck file offset unsigned in QAPI, Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 34/56] block: Make BlockDeviceStats sizes, offsets unsigned in QAPI/QMP, Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 53/56] block: Make blockdev-add byte counts unsigned in QAPI/QMP, Markus Armbruster, 2017/08/07
- [Qemu-devel] [RFC PATCH 37/56] blockjob: Make BlockJobInfo and event speed unsigned in QAPI/QMP, Markus Armbruster, 2017/08/07