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

[Max Reitz]

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.

Max

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