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

[John Snow]

On 10/15/19 4:44 AM, Kevin Wolf wrote:
> Am 14.10.2019 um 20:10 hat John Snow geschrieben:
>>
>>
>> On 10/11/19 7:18 PM, John Snow wrote:
>>>
>>>
>>> On 10/11/19 5:48 PM, Eric Blake wrote:
>>>> On 10/11/19 4:25 PM, John Snow wrote:
>>>>> From: Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com>
>>>>>
>>>>> 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 <vsementsov at virtuozzo.com>
>>>>> Reviewed-by: Max Reitz <mreitz at redhat.com>
>>>>> Message-Id: <20190806152611.280389-1-vsementsov at virtuozzo.com>
>>>>> [Maintainer edit: Max's suggestions from on-list. --js]
>>>>> Signed-off-by: John Snow <jsnow at redhat.com>
>>>>> ---
>>>>>   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.
>>
>> I've noticed that seasoned C programmers hate extra parentheses a lot.
>> I've noticed that I cannot remember operator precedence enough to ever
>> feel like this is actually an improvement.
>>
>> Something about a nice weighted tree of ((expr1) || (expr2)) feels
>> soothing to my weary eyes. So, if it's not terribly important, I'd
>> prefer to leave it as-is.
> 
> I don't mind the parentheses, but I do prefer QEMU_IS_ALIGNED() to the
> open-coded version. Would that be a viable compromise?
> 

Oh, I'm sorry! I did change that. I didn't mean to appear any more
stubborn than I actually am.

--js