qemu-stable
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-stable] [PATCH v2] bitmap: Update count after a merge


From: John Snow
Subject: Re: [Qemu-stable] [PATCH v2] bitmap: Update count after a merge
Date: Wed, 3 Oct 2018 15:57:11 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1


On 10/03/2018 10:49 AM, Eric Blake wrote:
> On 10/3/18 9:32 AM, Vladimir Sementsov-Ogievskiy wrote:
>> 03.10.2018 02:33, John Snow wrote:
>>> From: Eric Blake <address@hidden>
>>>
>>> We need an accurate count of the number of bits set in a bitmap
>>> after a merge. In particular, since the merge operation short-circuits
>>> a merge from an empty source, if you have bitmaps A, B, and C where
>>> B started empty, then merge C into B, and B into A, an inaccurate
>>> count meant that A did not get the contents of C.
>>>
>>> In the worst case, we may falsely regard the bitmap as empty when
>>> it has had new writes merged into it.
>>>
>>> Fixes: be58721db
>>> CC: address@hidden
>>> Signed-off-by: Eric Blake <address@hidden>
>>> Signed-off-by: John Snow <address@hidden>
>>
>> Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>
>> Hm, I rememberd:
>> commit 3260cdfffbf00f33923f5f9f6bef45932d7ac28b
>> Author: Liang Li <address@hidden>
>> Date:   Wed Feb 7 11:35:49 2018 -0500
>>
>>       hbitmap: fix missing restore count when finish deserialization
>>
>>       The .count of HBitmap is forgot to set in function
>>       hbitmap_deserialize_finish, let's set it to the right value.
>>
>>
>>    - I always forget to update this field.. We definitely should add some
>> generic check on it somewhere, at least in tests.
> 
> My suggestion (in another thread) was to enhance
> x-debug-block-dirty-bitmap-sha256 to include 'count' alongside the
> checksum, to make it easier to write such tests.
> 

I suppose this is in preference to query-block? It would make it easier.

--js



reply via email to

[Prev in Thread] Current Thread [Next in Thread]