16.01.2019 16:05, Max Reitz wrote:
> 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 <vsement...@virtuozzo.com>
>>>>>> ---
>>>>>> 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).
This will not work, as ((offset + bytes) / job->cluster_size) is not first
clean cluster
or end cluster. It's a cluster, where is first clean bit located, but it may
have dirty
bits too (or, may not).
So, to rewrite based on end_cluster, it should be calculated as
(offset + bytes - 1) / job->cluster_size + 1
and, I'm going to do so, one "+1" instead of two, and, may be, a bit more
understandable.
--
Best regards,
Vladimir
