Re: [PATCH v2 2/6] parallels.txt: fix bitmap L1 table description

["Denis V. Lunev" <den@openvz.org>]

On 2/24/21 1:47 PM, Vladimir Sementsov-Ogievskiy wrote:
> Actually L1 table entry offset is in 512 bytes sectors. Fix the spec.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  docs/interop/parallels.txt | 27 +++++++++++++++------------
>  1 file changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/docs/interop/parallels.txt b/docs/interop/parallels.txt
> index f15bf35bd1..73af9a2c4b 100644
> --- a/docs/interop/parallels.txt
> +++ b/docs/interop/parallels.txt
> @@ -208,21 +208,24 @@ of its data area are:
>    28 - 31:    l1_size
>                The number of entries in the L1 table of the bitmap.
>  
> -  variable:   l1_table (8 * l1_size bytes)
> -              L1 offset table (in bytes)
> +  variable:   L1 offset table (l1_table), size: 8 * l1_size bytes
>  
> -A dirty bitmap is stored using a one-level structure for the mapping to host
> -clusters - an L1 table.
> +Dirty bitmap is stored in the array of clusters inside Parallels Image file.
> +Offsets of these clusters are saved in L1 offset table here. Each L1 table
> +entry is a 64bit integer described below:
>  
> -Given an offset in bytes into the bitmap data, the offset in bytes into the
> -image file can be obtained as follows:
> +Given an offset in bytes into the bitmap data, corresponding L1 entry is
>  
> -    offset = l1_table[offset / cluster_size] + (offset % cluster_size)
> +    l1_table[offset / cluster_size]
>  
> -If an L1 table entry is 0, the corresponding cluster of the bitmap is assumed
> -to be zero.
> +If L1 table entry is 0, all bits in the corresponding cluster of the bitmap
> +are assumed to be 0.
>  
> -If an L1 table entry is 1, the corresponding cluster of the bitmap is assumed
> -to have all bits set.
> +If L1 table entry is 1, all bits in the corresponding cluster of the bitmap
> +are assumed to be 1.
>  
> -If an L1 table entry is not 0 or 1, it allocates a cluster from the data area.
> +If an L1 table entry is not 0 or 1, it contains corresponding cluster offset
> +(in 512b sectors). Given an offset in bytes into the bitmap data the offset in
> +bytes into the image file can be obtained as follows:
> +
> +    offset = l1_table[offset / cluster_size] * 512 + (offset % cluster_size)
Reviewed-by: Denis V. Lunev <den@openvz.org>