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

[Vladimir Sementsov-Ogievskiy]

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;

> 
> Max
> 


-- 
Best regards,
Vladimir