Re: [Qemu-devel] [PATCH v5 01/11] block/backup: simplify backup_incremental_init_copy_bitmap

[Max Reitz]

On 14.01.19 15:48, Vladimir Sementsov-Ogievskiy wrote:
> 14.01.2019 17:13, Max Reitz wrote:
>> On 14.01.19 15:01, Vladimir Sementsov-Ogievskiy wrote:
>>> 14.01.2019 16:10, Max Reitz wrote:
>>>> On 29.12.18 13:20, Vladimir Sementsov-Ogievskiy wrote:
>>>>> Simplify backup_incremental_init_copy_bitmap using the function
>>>>> bdrv_dirty_bitmap_next_dirty_area.
>>>>>
>>>>> Note: move to job->len instead of bitmap size: it should not matter but
>>>>> less code.
>>>>>
>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>>>> ---
>>>>>    block/backup.c | 40 ++++++++++++----------------------------
>>>>>    1 file changed, 12 insertions(+), 28 deletions(-)
>>>>
>>>> Overall: What is this function even supposed to do?  To me, it looks
>>>> like it marks all areas in job->copy_bitmap dirty that are dirty in
>>>> job->sync_bitmap.
>>>>
>>>> If so, wouldn't just replacing this by hbitmap_merge() simplify things
>>>> further?
>>>>
>>>>> diff --git a/block/backup.c b/block/backup.c
>>>>> index 435414e964..fbe7ce19e1 100644
>>>>> --- a/block/backup.c
>>>>> +++ b/block/backup.c
>>>>> @@ -406,43 +406,27 @@ static int coroutine_fn 
>>>>> backup_run_incremental(BackupBlockJob *job)
>>>>
>>>> [...]
>>>>
>>>>> +    while (bdrv_dirty_bitmap_next_dirty_area(job->sync_bitmap,
>>>>> +                                             &offset, &bytes))
>>>>> +    {
>>>>> +        uint64_t cluster = offset / job->cluster_size;
>>>>> +        uint64_t last_cluster = (offset + bytes) / job->cluster_size;
>>>>>    
>>>>> -        next_cluster = DIV_ROUND_UP(offset, job->cluster_size);
>>>>> -        hbitmap_set(job->copy_bitmap, cluster, next_cluster - cluster);
>>>>> -        if (next_cluster >= end) {
>>>>> +        hbitmap_set(job->copy_bitmap, cluster, last_cluster - cluster + 
>>>>> 1);
>>>>
>>>> Why the +1?  Shouldn't the division for last_cluster round up instead?
>>>>
>>>>> +
>>>>> +        offset = (last_cluster + 1) * job->cluster_size;
>>>>
>>>> Same here.
>>>
>>> last cluster is not "end", but it's last dirty cluster. so number of dirty 
>>> clusters is last_cluster - cluster + 1, and next offset is calculated 
>>> through +1 too.
>>>
>>> If I round up division result, I'll get last for most cases, but "end" 
>>> (next after the last), for the case when offset % job->cluster_size == 0, 
>>> so, how to use it?
>>
>> Doesn't bdrv_dirty_bitmap_next_dirty_area() return a range [offset,
>> offset + bytes), i.e. where "offset + bytes" is the first clean offset?
> 
> oops, you are right. then I need
> uint64_t last_cluster = (offset + bytes - 1) / job->cluster_size;

That, or you just use a rounding up division and rename it from
last_cluster to end_cluster or first_clean_cluster or something (and
subsequently drop the +1s).

Max

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