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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: |
Tue, 15 Oct 2019 08:55:07 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 |
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 <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.
>>
>> 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
[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 05/19] block/dirty-bitmap: drop meta, John Snow, 2019/10/11
[PULL 04/19] block/qcow2: proper locking on bitmap add/remove paths, 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
[PULL 09/19] block: switch reopen queue from QSIMPLEQ to QTAILQ, John Snow, 2019/10/11
[PULL 10/19] block: reverse order for reopen commits, John Snow, 2019/10/11
[PULL 11/19] iotests: add test-case to 165 to test reopening qcow2 bitmaps to RW, John Snow, 2019/10/11