Re: [Qemu-devel] [PATCH v2] util/hbitmap: strict hbitmap_reset

[John Snow]

On 9/11/19 11:13 AM, Vladimir Sementsov-Ogievskiy wrote:
> 07.08.2019 19:27, John Snow wrote:
>>
>>
>> On 8/6/19 12:19 PM, Vladimir Sementsov-Ogievskiy wrote:
>>> 06.08.2019 19:09, Max Reitz wrote:
>>>> On 06.08.19 17:26, Vladimir Sementsov-Ogievskiy wrote:
>>>>> 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>
>>>>> ---
>>>>>
>>>>> v2 based on Max's https://github.com/XanClic/qemu.git block
>>>>> which will be merged soon to 4.1, and this patch goes to 4.2
>>>>> Based-on: https://github.com/XanClic/qemu.git block
>>>>>
>>>>> v1 was "[PATCH] util/hbitmap: fix unaligned reset", and as I understand
>>>>> we all agreed to just assert alignment instead of aligning down
>>>>> automatically.
>>>>>
>>>>>    include/qemu/hbitmap.h | 5 +++++
>>>>>    tests/test-hbitmap.c   | 2 +-
>>>>>    util/hbitmap.c         | 4 ++++
>>>>>    3 files changed, 10 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
>>>>> index 4afbe6292e..7865e819ca 100644
>>>>> --- a/include/qemu/hbitmap.h
>>>>> +++ b/include/qemu/hbitmap.h
>>>>> @@ -132,6 +132,11 @@ void hbitmap_set(HBitmap *hb, uint64_t start, 
>>>>> uint64_t count);
>>>>>     * @count: Number of bits to reset.
>>>>>     *
>>>>>     * Reset a consecutive range of bits in an HBitmap.
>>>>> + * @start and @count must be aligned to bitmap granularity. The only 
>>>>> exception
>>>>> + * is resetting the tail of the bitmap: @count may be equal to @start +
>>>>> + * hb->orig_size,
>>>>
>>>> s/@start + hb->orig_size/hb->orig_size - @start/, I think.
>>>
>>> Ha, I wanted to say start + count equal to orig_size. Yours is OK too of 
>>> course.
>>>
>>>>
>>>>>       in this case @count may be not aligned. @start + @count
>>>>
>>>> +are
>>>>
>>>> With those fixed:
>>>>
>>>> Reviewed-by: Max Reitz <address@hidden>
>>>
>>> Thanks!
>>>
>>
>> I'll add this to the pile for 4.2, after I fix the rebase conflicts that
>> arose from 4.1-rc4.
>>
> 
> Hi!
> 
> Didn't you forget, or should I resend?
> 
> 

I must have dropped the patch by accident during the rebasing. As an
apology, I squashed in Max's suggestions from the list. Check that they
look OK, please?

Thanks, applied to my bitmaps tree:

https://github.com/jnsnow/qemu/commits/bitmaps
https://github.com/jnsnow/qemu.git

--js