Re: [PATCH 2/5] parallels.txt: fix bitmap L1 table description

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

On 2/16/21 7:45 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 | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/docs/interop/parallels.txt b/docs/interop/parallels.txt
> index f15bf35bd1..ebbdd1b25b 100644
> --- a/docs/interop/parallels.txt
> +++ b/docs/interop/parallels.txt
> @@ -209,15 +209,14 @@ of its data area are:
>                The number of entries in the L1 table of the bitmap.
>  
>    variable:   l1_table (8 * l1_size bytes)
> -              L1 offset table (in bytes)
this change is unclear. First, we have specified here the size of this
table. It is (8 * l1_size bytes). Thus it would be MUCH better to say

l1_table (size: 8 * l1_size bytes)

or

L1 offset table (l1_table), size: 8 * l1_size bytes
or something like this.


>  
>  A dirty bitmap is stored using a one-level structure for the mapping to host
> -clusters - an L1 table.
> +clusters - an L1 table. 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]
Dirty bitmap is stored in the array of clusters inside Parallels Image file.
Offsets of these clusters are saved in L1 offset table here.


>  
>  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.


> @@ -225,4 +224,8 @@ to be zero.
>  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)
looks good