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Re: [PULL 01/19] util/hbitmap: strict hbitmap_reset
From: |
John Snow |
Subject: |
Re: [PULL 01/19] util/hbitmap: strict hbitmap_reset |
Date: |
Fri, 11 Oct 2019 19:18:42 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 |
On 10/11/19 5:48 PM, Eric Blake wrote:
> On 10/11/19 4:25 PM, John Snow wrote:
>> From: Vladimir Sementsov-Ogievskiy <address@hidden>
>>
>> hbitmap_reset has an unobvious property: it rounds requested region up.
>> It may provoke bugs, like in recently fixed write-blocking mode of
>> mirror: user calls reset on unaligned region, not keeping in mind that
>> there are possible unrelated dirty bytes, covered by rounded-up region
>> and information of this unrelated "dirtiness" will be lost.
>>
>> Make hbitmap_reset strict: assert that arguments are aligned, allowing
>> only one exception when @start + @count == hb->orig_size. It's needed
>> to comfort users of hbitmap_next_dirty_area, which cares about
>> hb->orig_size.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>> Reviewed-by: Max Reitz <address@hidden>
>> Message-Id: <address@hidden>
>> [Maintainer edit: Max's suggestions from on-list. --js]
>> Signed-off-by: John Snow <address@hidden>
>> ---
>> include/qemu/hbitmap.h | 5 +++++
>> tests/test-hbitmap.c | 2 +-
>> util/hbitmap.c | 4 ++++
>> 3 files changed, 10 insertions(+), 1 deletion(-)
>>
>
>> +++ b/util/hbitmap.c
>> @@ -476,6 +476,10 @@ void hbitmap_reset(HBitmap *hb, uint64_t start,
>> uint64_t count)
>> /* Compute range in the last layer. */
>> uint64_t first;
>> uint64_t last = start + count - 1;
>> + uint64_t gran = 1ULL << hb->granularity;
>> +
>> + assert(!(start & (gran - 1)));
>> + assert(!(count & (gran - 1)) || (start + count == hb->orig_size));
>
> I know I'm replying a bit late (since this is now a pull request), but
> would it be worth using the dedicated macro:
>
> assert(QEMU_IS_ALIGNED(start, gran));
> assert(QEMU_IS_ALIGNED(count, gran) || start + count == hb->orig_size);
>
> instead of open-coding it? (I would also drop the extra () around the
> right half of ||). If we want it, that would now be a followup patch.
>
If the PR doesn't make it for some reason, I can amend a cleanup patch
for the next PR.
--js
[PULL 02/19] block: move bdrv_can_store_new_dirty_bitmap to block/dirty-bitmap.c, John Snow, 2019/10/11
[PULL 03/19] block/dirty-bitmap: return int from bdrv_remove_persistent_dirty_bitmap, John Snow, 2019/10/11
[PULL 04/19] block/qcow2: proper locking on bitmap add/remove paths, John Snow, 2019/10/11
[PULL 05/19] block/dirty-bitmap: drop meta, John Snow, 2019/10/11
[PULL 07/19] block/dirty-bitmap: drop BdrvDirtyBitmap.mutex, John Snow, 2019/10/11
[PULL 06/19] block/dirty-bitmap: add bs link, John Snow, 2019/10/11
[PULL 08/19] block/dirty-bitmap: refactor bdrv_dirty_bitmap_next, John Snow, 2019/10/11