[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PULL 01/19] util/hbitmap: strict hbitmap_reset
From: |
John Snow |
Subject: |
Re: [PULL 01/19] util/hbitmap: strict hbitmap_reset |
Date: |
Mon, 14 Oct 2019 14:10:09 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 |
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.
(You may feel free to counter-educate me as desired.)
>>
>
> If the PR doesn't make it for some reason, I can amend a cleanup patch
> for the next PR.
>
by the way: GOOD NEWS! ...
--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 04/19] block/qcow2: proper locking on bitmap add/remove paths, John Snow, 2019/10/11
[PULL 05/19] block/dirty-bitmap: drop meta, 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