Re: [PULL 01/19] util/hbitmap: strict hbitmap_reset

[John Snow]

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